Methods

Randomised controlled trial.

Participants

40 women.

Inclusion criteria: pregnant women aged 18 to 40 years diagnosed with GDM by a 100 g OGTT (see notes) at 24 to 28 weeks' gestation.

Exclusion criteria: untreated hypothyroidism, smoking, kidney or liver diseases, taking oestrogen therapies.

Setting: Iran.

Interventions

DASH diet (n = 20 randomised; 17 analysed)

• The macronutrient composition of the DASH diet was similar to the control diet (45% to 55% total daily energy intake from carbohydrates, 15% to 20% from protein and 25% to 30% from fat).

• DASH diet was rich in fruits, vegetables, whole grains and low‐fat dairy products, and low in saturated fats, cholesterol, refined grains and sweets.

• The amount of sodium intake was 2400 mg/day.

• For a duration of 4 weeks.

Control diet with matching macronutrients (n = 20 randomised; 17 analysed)

• 45% to 55% total daily energy intake from carbohydrates, 15% to 20% from protein and 25% to 30% from fat.

• For a duration of 4 weeks.

All women:

• All women were asked not to alter their routine physical activity, not to take any anti‐hyperglycaemic or lipid‐lowering medications during the 4‐week intervention.

• All pregnant women consumed a supplement of calcium and ferfolic once a day.

• Adherence to the diets was monitored once a week through phone interviews. The compliance was double‐checked by the use of 3‐day dietary records completed throughout the study.

Outcomes

Data in meta‐analyses for: hypertensive disorders of pregnancy (pre‐eclampsia); caesarean section; birthweight; gestational weight gain (BMI and weight at the end of intervention); use of additional pharmacotherapy; glycaemic control (end of intervention fasting blood glucose; end of intervention HbA1c).

Notes

GDM diagnosis based on ADA criteria: 2 or more values met or exceeded the following 100 g 3‐hour OGTT:

• Fasting: 5.3 mmol/L;

• 1 hour: 10.0 mmol/L;

• 2 hour: 8.6 mmol/L;

• 3 hour: 7.8 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Described as "Random assignment was done by the use of computer‐generated random numbers".

Allocation concealment (selection bias)

Unclear risk

Described as above; no further details provided regarding allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes

Low risk

Described as "with the exception of the study dietitian, who provided the dietary education, all study personnel and participants were blinded to the dietary assignment".

Although the study dietitian was not blinded, all other research personnel were reported to be blinded, and thus the risk of performance bias was judged to be low.

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

Described as above and the un‐blinded dietitian was not involved in outcome data collection.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Post‐randomisation exclusions:

3 in the DASH diet group: pre‐eclampsia (n = 2) and complete bed rest (n = 1).

3 in the control diet group: pre‐eclampsia (n = 2) and insulin therapy (n = 1).

No losses to follow‐up.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting. Data reported for a limited number of review outcomes.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

38 women.

Inclusion criteria: pregnant women aged 18 to 40 years, diagnosed with GDM by a 100 g OGTT (see notes) at 24 to 28 weeks' gestation; no previous history of GDM, non‐smoker.

Exclusion criteria: premature preterm rupture of membrane, placental abruption, pre‐eclampsia, need to commence insulin therapy or on insulin therapy, recommendation for complete bed rest.

Setting: Iran.

Interventions

DASH diet (n = 19 randomised; 16 analysed)

• The macronutrient composition of the DASH diet was similar to the control diet (45% to 55% total daily energy intake from carbohydrates, 15% to 20% from protein and 25% to 30% from fat).

• DASH diet was rich in fruits, vegetables, whole grains and low‐fat dairy products, and low in saturated fats, cholesterol, refined grains and sweets.

• The amount of sodium intake was restricted to < 2000 mg/day.

• Diet was planned as a 7‐day menu cycle, for a duration of 4 weeks.

Control diet with matching macronutrients (n = 19 randomised; 16 analysed)

• 45% to 55% total daily energy intake from carbohydrates, 15% to 20% from protein and 25% to 30% from fat.

• Diet was planned as a 7 day menu cycle, for a duration of 4 weeks.

All women:

• All women were asked not to alter their routine physical activity.

• All women were consuming a daily supplement of calcium and ferfolic.

• Compliance with the consumption of diets was monitored weekly through phone interviews; compliance was double‐checked by the use of 3‐day dietary records completed throughout the study.

Outcomes

Data in meta‐analyses for: hypertensive disorders of pregnancy (pre‐eclampsia); gestational weight gain (BMI and weight at end of intervention); insulin sensitivity (end of intervention insulin and HOMA‐IR); glycaemic control (end of intervention fasting blood glucose).

Notes

GDM diagnosis based on ADA criteria: 2 or more values met or exceeded following 100 g 3‐hour OGTT;

• Fasting: 5.3 mmol/L;

• 1 hour: 10.0 mmol/L;

• 2 hour: 8.6 mmol/L;

• 3 hour: 7.8 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Described as "random assignment was done by the use of computer‐generated random numbers. A trained midwife at the maternity clinic performed randomization".

Allocation concealment (selection bias)

Unclear risk

Described as above; no further details provided regarding allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes

Low risk

Described as "with the exception of the study dietitian, who provided the dietary education, all study personnel and participants were blinded to the dietary assignment".

Although the study dietitian was not blinded, all other research personnel were reported to be blinded, and thus the risk of performance bias was judged to be low.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

It was unclear whether the un‐blinded dietitian was involved in outcome assessment.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Post‐randomisation exclusions:

3 in the DASH diet group: pre‐eclampsia (n = 2) and complete bed rest (n = 1).

3 in the control diet group: pre‐eclampsia (n = 2) and insulin therapy (n = 1).

No losses to follow‐up.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting. Data reported for a limited number of review outcomes.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

58 women.

Inclusion criteria: primigravid pregnant women aged 18 to 40 years, diagnosed with GDM by a 100 g OGTT (see notes) at 24 to 28 weeks' gestation.

Exclusion criteria: previous glucose intolerance or GDM diagnosis, premature preterm rupture of membrane, placenta abruption, pre‐eclampsia, requiring insulin therapy during intervention or complete bed rest, hypothyroidism, urinary tract infection, smoking and kidney or liver diseases, taking oestrogen therapy.

Setting: Iran.

Interventions

DASH diet (n = 29 randomised; 26 analysed)

• The calorie content and protein composition of the DASH diet was similar to the control diet (45% to 55% total daily energy intake from carbohydrates, 15% to 20% from protein and 25% to 30% from fat).

• DASH diet was rich in fruits, vegetables, whole grains and low‐fat dairy products, and low in saturated fats, cholesterol, refined grains and sweets.

• The amount of sodium intake was 2400 mg/day.

• For a duration of 4 weeks.

Control diet with matching macronutrients (n = 19 randomised; 26 analysed)

• 45% to 55% total daily energy intake from carbohydrates, 15% to 20% from protein and 25% to 30% from fat.

• For a duration of 4 weeks.

All women:

• All women were asked not to alter their routine physical activity, not to take any anti‐hyperglycaemic or lipid‐lowering medications during the 4‐week intervention.

• All pregnant women were also consuming 400 mg/day folic acid from the beginning of pregnancy and 50 mg/day ferrous sulphate as well as multivitamin–mineral supplements from 20 weeks' gestation.

• Compliance with the consumption of diets was monitored once a week through phone interviews; compliance was double checked by the use of 3‐day (2 week days and 1 weekend day) dietary records completed throughout the study.

Outcomes

Data in meta‐analyses for: hypertensive disorders of pregnancy (pre‐eclampsia); caesarean section; gestational age at birth; macrosomia; birthweight; head circumference at birth; length at birth; ponderal index at birth; placental abruption; use of additional; pharmacotherapy.

Notes

GDM diagnosis based on ADA criteria: 2 or more values met or exceeded following 100g 3‐hour OGTT;

• Fasting: 5.3 mmol/L;

• 1 hour: 10.0 mmol/L;

• 2 hour: 8.6 mmol/L;

• 3 hour: 7.8 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Described as "random assignment was done using computer‐generated random numbers".

Allocation concealment (selection bias)

Unclear risk

Described as above; no further detail provided regarding allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes

Unclear risk

No information about whether women or personnel were blinded.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information about whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Post‐randomisation exclusions:

3 in the DASH diet group: pre‐eclampsia (n = 1), placenta abruption (n = 1) and complete bed rest (n = 1).

3 in the control diet group: premature preterm rupture of membrane (n = 1), needed to commence insulin therapy during intervention (n = 1) and pre‐eclampsia (n = 1).

No losses to follow‐up.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting. Data reported for a limited number of review outcomes.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

37 women. A total of 69 women were involved in the trial, but only 37 women were diagnosed with GDM and provided outcome data for this review.

Inclusion criteria: women ≤ 30 weeks' gestation, diagnosed with type A2 GDM (see notes), who were planning to give birth at the NIPerIER and required medical treatment from the Department of Endocrinology.

Exclusion criteria: women with type 1 diabetes, type A1 GDM (see notes), glucose intolerance, multiple pregnancies, kidney or liver disease and hyperthyroidism or hypothyroidism.

Setting: Mexico.

Interventions

Low‐moderate GI diet (n = 19)

Only foods with a low‐to‐moderate GI were recommended.

Moderate‐high GI diet (n = 18)

Control group: any type of carbohydrate was permitted.

All women:

• Received medical nutrition therapy from a nutritionist and diabetes educator, which included a complete evaluation of nutritional status, nutritional intervention based on a moderate restriction of calorie (24 kcal/kg) and carbohydrate (40% to 45%) intake.

• Weight, weight gain, glycaemic control and initiation of or any alteration to insulin treatment were evaluated in each consultation.

• Received a glucose meter and a finger prick device; frequent capillary glucose self‐monitoring (6 times a day) as an intense educational component.

• Were informed about the importance of measuring their glucose concentrations, how to use the glucose meter and about the recording of capillary glucose readings.

Outcomes

Data in meta‐analyses for: use of additional pharmacotherapy.

Notes

• No GDM diagnostic criteria reported.

• Type A1 GDM: abnormal OGTT but normal blood glucose during fasting and 2 hours after meals; diet modification sufficient to control glucose concentrations.

• Type A2 GDM: abnormal OGTT compounded by abnormal glucose during fasting and/or after meals; additional therapy with insulin or other medications required.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Described as "women included in this study were randomly divided into two study groups", no further information available.

Allocation concealment (selection bias)

Unclear risk

No information was provided regarding allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

It is unlikely that women were able to be blinded due to the nature of behavioural intervention used in this study. No information on whether research personnel were able to be blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information about whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

High risk

Of the total randomised cohort of 108 eligible women (mixed cohort of women with GDM and type 2 diabetes) in a clinical trial, 20 declined (15.8%) to participate in the trial with reasons unclear. Another 19 women (17.5%) were excluded due to incomplete dietary information. No information was available for these excluded participants.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting; information obtained from translation.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

99 women.

Inclusion criteria: women aged 18 to 50 years; 24th to 26th weeks of gestational age; diagnosed with GDM by a 75 g OGTT (see notes); singleton pregnancies.

Exclusion criteria: BMI > 40 kg/m², any known diseases, medications or obstetric absolute or relative contraindications to exercise.

Setting: Italy.

Interventions

Diet recommendation and diet‐related behavioural advice (n = 49)

• Individually prescribed diet: daily total energy divided as carbohydrate: 48% to 50%, protein: 18% to 20%, fat: 30% to 35%; fibre 20 to 25 g/day; no alcohol.

• Individual oral or written recommendations for helping with healthy dietary choices (i.e. lowering carbohydrate intake, strategies for out‐of‐home eating, healthy cooking and food shopping and related behavioural suggestions).

• Debunking false myths about diet in pregnancy.

Diet recommendation only (n = 50)

• Individually‐prescribed diet: daily total energy divided as carbohydrate: 48% to 50%, protein: 18% to 20%, fat: 30% to 35%; fibre 20 to 25 g/day, no alcohol.

All women:

• Patients were monitored by weekly phone calls and visited every 2 weeks to monitor adverse events and protocol adherence (for intervention group: consuming at least 18% protein, 20 g/day fibre, abolishing alcohol).

• Patients self‐monitored capillary blood glucose 4 to 6 times/day (preprandial and 2‐hour postprandial).

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; caesarean section; preterm birth; gestational weight gain (BMI and weight at end of intervention); insulin sensitivity (end of intervention insulin, HOMA‐IR); use of additional pharmacotherapy; glycaemic control (end of intervention fasting glucose, postprandial glucose, HbA1c); length of postnatal stay (baby; > 4 days).

Notes

GDM was diagnosed by 75 g OGTT; no diagnostic criteria specified.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Described as "randomization was stratified by baseline body mass index (BMI) and METs, and was implemented through a website (www.epiclin.it)".

Allocation concealment (selection bias)

Low risk

Described as above.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

It is considered unlikely that women were able to be blinded.

Blinding of outcome assessment (detection bias)
All outcomes

Low risk

"The dieticians, the obstetricians who reported maternal/neonatal complications, and the laboratory personnel were blinded to the group assignment."

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No loss to follow‐up or post‐randomisation exclusions.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol, not able to confidently assess the risk of selective reporting. Trial registration reports birthweight as a secondary outcome, however data not reported for this outcome in the manuscript.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

30 women.

Inclusion criteria: Caucasian women with newly diagnosed GDM (see notes).

Exclusion criteria: not reported.

Setting: Poland.

Interventions

Low‐carbohydrate diet (n = 15)

Daily total energy divided as carbohydrate: 45%, protein: 25%, fat: 30% (based on daily total energy of 1800 kcal). Women were encouraged to have the diet until birth.

High‐carbohydrate diet (n = 15)

Daily total energy divided as carbohydrate: 60%, protein: 25%, fat: 15% (based on daily total energy of 1800 kcal). Women were encouraged to follow the diet until birth.

All women:

• Blood glucose was recorded from the women's diaries 3 to 4 days before study intervention.

• During the first 14 days after the start of interventions, women were asked to monitor their blood glucose at home 4 times a day (fasting and 2 hours after breakfast, lunch and dinner); results were recorded in the home blood glucose monitoring diary.

• On day 15, compliance to nutritional recommendations was assessed; diary reviewed.

• Urine ketones were checked daily.

Outcomes

Data in meta‐analyses for: caesarean section; gestational age at birth; macrosomia; birthweight; normal vaginal birth; operative vaginal birth; adherence to dietary intervention; use of additional pharmacotherapy; glycaemic control (end of intervention fasting and post breakfast, lunch and dinner 2‐hour blood glucose).

Notes

GDM diagnosis based on WHO criteria: 1 or more value met or exceeded:

• Fasting ≥ 7.0 mmol/L;

• 2 hours after 75 g glucose load ≥ 7.8 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Described as "the patients were randomised into two groups"; no further details available.

Allocation concealment (selection bias)

Unclear risk

No information was provided regarding allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

It is considered unlikely that women were able to be blinded. No information on whether research personnel were able to be blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information about whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No loss to follow‐up or post‐randomisation exclusions.

Selective reporting (reporting bias)

High risk

Maternal weight gain was reported incompletely "The proper weight change was observed in all the patients studied;" and data reported for a limited number of review outcomes. No access to study protocol to further assess the risk of selective reporting.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

300 women.

Inclusion criteria: pregnant women diagnosed with GDM (see notes) between 24 and 32 weeks' gestation in otherwise low‐risk pregnancies.

Exclusion criteria: multiple gestation; maternal‐fetal blood group incompatibility; known congenital anomaly; prior evidence of placenta praevia or abruptio placentae; significant maternal disease including chronic hypertension, connective tissue disease, endocrine disorders, and chronic hepatic disease; long‐term medical therapy affecting glucose metabolism such as steroids and β‐mimetic tocolytic agents; and imminent birth.

Setting: Canada.

Interventions

Energy‐restricted diet (n = 150 randomised; 149 analysed)

• Women received dietary counselling and were placed on a calorie‐restricted diet of 35 kcal/kg ideal body weight per day, with emphasis on spacing of meals and snacks to avoid major glucose fluctuations. Women were also taught home glucose monitoring techniques with semi‐quantitative whole blood glucose reagent strips.

• If fasting or postprandial plasma glucose concentrations exceeded targeted values (fasting glucose concentrations < 4.4 mmol/L and 1‐hour postprandial glucose concentrations < 7.8 mmol/L) on diet alone on 2 or more occasions, insulin supplementation was added to the regimen, and the dosage was individualised and closely monitored.

• Women were seen bi‐weekly, and biophysical profiles were performed at each visit, with ultrasonographic assessment of fetal growth, amniotic fluid volume, and cardiac size.

No energy‐restricted diet (n = 150 randomised and analysed)

• Women were asked to continue an unrestricted healthy diet for pregnancy according to the standards of the Canada Food Guide.

• Women performed 2 glucose concentrations weekly at home with semi‐quantitative whole blood glucose reagent strips.

• The women returned to their primary obstetric care provider and were not seen again in the GDM teaching unit.

• 'Failed control': if women in the no energy‐restricted diet group had persistent fasting capillary blood glucose > 7.8 mmol/L or 1‐hour postprandial concentration > 11.1 mmol/L, they were transferred to the treatment arm and placed on diet, insulin, and fetal monitoring.

Outcomes

Data in meta‐analyses for: perinatal mortality; caesarean birth; stillbirth; neonatal mortality; gestational age at birth; macrosomia; birthweight; shoulder dystocia; bone fracture; nerve palsy; neonatal hypoglycaemia; hyperbilirubinaemia; hypocalcaemia; normal vaginal birth; gestational weight gain (weight at birth); use of additional pharmacotherapy; glycaemic control (during and end of intervention fasting and postprandial 1‐hour glucose).

Notes

Intention‐to‐treat analysis: data from 'failed control' group was analysed with the no energy‐restricted diet group data.

Hatem criteria used for GDM diagnosis: following 75 g OGTT

• 2 hour: > 7.5 mmol/L for the second trimester;

• 2 hour: > 9.6 mmol/L for the third trimester.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Described as "those women who agreed to participate in the study signed an informed consent form and were randomly allocated to treatment or control groups by randomisation tables".

Allocation concealment (selection bias)

Unclear risk

No further detail regarding allocation concealment provided.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

It is unlikely that study women were able to be blinded. It was reported that healthcare workers involved in the trial were blinded to the home blood glucose monitoring results for women in the no energy‐restricted diet group; no further information was available.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

1 woman from the energy‐restricted diet group was lost to follow‐up. No post‐randomisation exclusions or withdrawals.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

Unclear risk

There were 16 women in the no energy‐restricted diet group who received the same interventions as those in the energy‐restricted diet group (failed control); intention‐to‐treat analysis was applied.

Methods

Randomised controlled trial.

Participants

29 women. A total of 43 women were involved in the trial, but only 29 women were diagnosed with GDM and provided outcome data for this review.

Inclusion criteria: pregnant women, 18 to 45 years, diagnosed with GDM (see notes), and who had been referred to the Diabetes in Pregnancy, St. Michael's Hospital, Canada.

Exclusion criteria: presence of a multiple pregnancy or an acute or chronic illness affecting carbohydrate metabolism; presence of type 1 or 2 diabetes prior to the current pregnancy; use of insulin treatment prior to providing consent; greater than 34 weeks' gestation; unable to communicate in English with no translator available.

Setting: Canada.

Interventions

Low‐moderate GI diet (n = 13)

Women were asked to select their starch choices from an exchange list of low‐GI foods.

Moderate‐high GI diet (n = 16)

Women were asked to select their starch choices from an exchange list of intermediate‐ and high‐GI foods, reflecting the usual intake of typical diabetes in pregnancy clinic patients.

All women:

• Standard medical nutrition therapy: patients were introduced to the Diabetes Food Guide and Canadian dietary recommendations to support a healthy pregnancy. A dietitian recommended how many starch choices/servings each woman should consume at each meal based upon their own individual gestational energy requirements and Acceptable Macronutrient Distribution Ranges.

• Provision of approximately $20 per week worth of non‐perishable study foods and all blood testing strips;

• Self‐monitoring of blood glucose from baseline to week 8: 4 times a day (fasting, 2 hours after breakfast, lunch and dinner);

• Insulin therapy initiated if lifestyle modification required were not made within 2 to 3 weeks.

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; macrosomia; use of additional pharmacotherapy.

Notes

CDA criteria used for GDM diagnosis: 2 of the values are met or exceeded following 76 g OGTT:

• Fasting: 5.3 mmol/L;

• 1 hour: 10.6 mmol/L;

• 2 hour: 8.9mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Randomisation order was created by 1 of the investigators who was not involved in recruitment. It is unclear how the sequence was generated; it was considered likely to be a computer‐generated sequence.

Allocation concealment (selection bias)

Low risk

Sealed, numbered, opaque envelopes were used, and various block sizes in randomisation were used.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Described as an "open‐label" pilot study.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

3 women in the low‐moderate GI group withdrew after randomisation, reasons given. Data were analysed on an intent‐to‐treat basis.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting. Data reported for a limited number of review outcomes.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

68 women.

Inclusion criteria: pregnant women with GDM (see notes), aged 18 to 40 years, at week 24 to 28 gestation.

Exclusion criteria: women with a fasting plasma glucose > 5.8 mmol/L and 2‐hour > 6.7 mmol/L ("because of ethical consideration, because they might needed insulin therapy"); with a history of diabetes (type 1 or 2 diagnosed in the current pregnancy), significant renal impairment, with premature preterm rupture of membranes, placental abruption, pre‐eclampsia, eclampsia, chronic hypertension or hypothyroidism.

Setting: Iran.

Interventions

Soy protein‐enriched diet (n = 34)

Diet containing 0.8 g/kg protein with 35% animal protein, 35% soy protein, and 30% other plant proteins. Women received textured soy protein (Sobhan) and were educated regarding the preparation of their meals with soy protein. A trained nutritionist explained that soy protein should be washed and soaked for 30 minutes and then cooked in boiling water with turmeric, lemon juice, and tomato paste for 10 minutes.

No soy protein diet (n = 34)

Diet containing 0.8 g/kg protein with 70% animal and 30% plant proteins.

All women:

• The duration of the supplementation was 6 weeks for both groups, and women were followed up until birth.

• All pregnant women were requested not to change their routine physical activity or usual dietary intakes during the study and not to consume any soy protein products other than those provided.

• All women followed the national supplementation guideline and consumed 400 µg/day of folic acid starting at the beginning of pregnancy and 60 mg/day of ferrous sulphate as of the second trimester.

• All patients provided 3 dietary recalls (once during the weekend and on 2 weekdays) and 3 physical activity records to verify that they maintained their usual diet and physical activity during the intervention. Both dietary recalls and physical activity records were taken at weeks 2, 4, and 6 of the intervention.

Outcomes

Data in meta‐analyses for: hypertensive disorders of pregnancy (pre‐eclampsia); caesarean section; gestational age at birth; preterm birth; macrosomia; birthweight; head circumference at birth; length at birth; neonatal hypoglycaemia; hyperbilirubinaemia; gestational weight gain (BMI and weight at end of intervention); insulin sensitivity (end of intervention HOMA‐IR; QUICKI; insulin); use of additional pharmacotherapy; glycaemic control (end of intervention fasting glucose); maternal hospitalisation; neonatal hospitalisations.

Notes

GDM was diagnosed by a "one‐step" 2 hour 75 g OGTT, based on the ADA criteria. GDM diagnosed when any of the values were met or exceeded:

• Fasting: ≥ 5.1 mmol/L;

• 1 hour: ≥ 10.0 mmol/L;

• 2 hour: ≥ 8.5 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Quote: "Randomization and allocation were done by a trained midwife and were masked from the researcher and patients until the main analyses were completed."

Allocation concealment (selection bias)

Unclear risk

As above.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

"Randomization and allocation were done by a trained midwife and were masked from the researcher and patients until the main analyses were completed." Considered unlikely to have been successful in view of the interventions.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

Not clearly reported.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

2 women from the no soy protein diet group were excluded "due to personal reasons"; however all women were included in the analyses.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting. Trial registered online, but retrospectively.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

27 women.

Inclusion criteria: women with GDM diagnosed by a positive 3‐hour 75 g OGTT (see notes) before the 34 weeks' gestation.

Exclusion criteria: use of any hypoglycaemic, anti‐lipidaemic or antihypertensive medication.

Setting: Denmark.

Interventions

High unsaturated fat diet (n = 13)

From 34 weeks' gestation women had a high‐monounsaturated fat diet; no details about high‐monounsaturated fat diet provided.

Low unsaturated fat diet (n = 14)

From 34 weeks' gestation women had a high‐carbohydrate diet; no details about high‐carbohydrate diet provided.

All women: after being diagnosed with GDM, all women were instructed to follow a high‐carbohydrate diet until the 34th week.

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; hypertensive disorders of pregnancy (pre‐eclampsia; hypertension); caesarean section; type 2 diabetes; gestational age at birth; macrosomia; birthweight; placental abruption; gestational weight gain (BMI and weight at birth); insulin sensitivity (during intervention); use of additional pharmacotherapy; glycaemic control (during intervention fasting and postprandial glucose, HbA1c); BMI postpartum; impaired glucose tolerance postpartum.

Notes

GDM diagnosis based on 3‐hour 75 g OGTT, bloods taken every 30 minutes; GDM was defined as 2 or more plasma glucose concentrations above 3 SD of the mean.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Reported as "the randomisation was performed block‐wise stratified for pre‐pregnancy weight with an expected ratio of obese to normal weight of three to one. The block sizes were six and two in the two strata".

Allocation concealment (selection bias)

Low risk

Reported as that "the randomisation was performed by a third person at an independent centre outside our institution, which produced information about the outcome of randomisation at baseline measurement in week 33".

Blinding of participants and personnel (performance bias)
All outcomes

High risk

It is unlikely that women were able to be blinded. No information on whether research personnel were able to be blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

Data were missing at multiple collection points for 1 to 2 women but this was explained in the text and was considered unlikely to impact outcomes. Only women who had a positive OGTT at early postnatal period or those who were unable to attend the early postnatal follow‐up, were followed up at ≥ 4 months postpartum, Therefore, there were only 6 women who provided outcome data for development of type 2 diabetes and 7 women provided outcome data for development of glucose intolerance at ≥ 4 months postpartum.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

High risk

Women in the high‐monounsaturated fat diet group had a higher trial entry BMI (mean (SD): 35 (2.4) kg/m²) when compared with women in the high‐carbohydrate group (mean (SD): 32.2 (1.5) kg/m²).

Methods

Randomised controlled trial.

Participants

99 women.

Inclusion criteria: women aged at 18 to 45 years, diagnosed with GDM by a 75 g OGTT (see notes) between 20 and 32 weeks' gestation, with an otherwise healthy singleton pregnancy.

Exclusion criteria: women who had special dietary requirements (including vegetarianism/veganism), pre‐existing diabetes, or pregnancy achieved by assisted reproduction and those who smoked or consumed alcohol during pregnancy.

Setting: Australia.

Interventions

Low‐GI diet (n = 50 randomised, 47 analysed)

Diet GI target of ≤ 50; other nutrients were the same as the comparison group.

High‐fibre moderate‐GI diet (n = 49 randomised, 45 analysed)

Diet GI target of around 60, which represented average GI of Australian population.

All women:

• Healthy diets of similar protein (15% to 25% total daily energy intake), fat (25% to 30% total daily energy intake), and carbohydrate (40% to 45% total daily energy intake) content;

• Completed 3‐day food record (2 weekdays and 1 weekend day) at baseline and 36 to 37 weeks' gestation;

• Received 2 food model booklet to assist in portion size estimation.

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; caesarean section; type 2 diabetes; gestational age at birth; preterm birth; macrosomia; small‐for‐gestational age; birthweight; head circumference at birth; length at birth; ponderal index; weight and height at 3 months postpartum; weight gain during pregnancy; adherence to intervention; insulin sensitivity (end of intervention HOMA‐IR, insulin); use of additional pharmacotherapy; glycaemic control (end of intervention blood glucose, HbA1c); return to pre‐pregnancy weight and BMI at 3 months postpartum; impaired glucose tolerance and insulin sensitivity at 3 months postpartum.

Notes

Insulin treatment was commenced if the mean fasting blood glucose or 1‐hour postprandial blood glucose in the preceding week exceeded 5.2 and 7.5 mmol/L, respectively.

ADIPS criteria used for GDM diagnosis: 1 or more value met or exceeded:

• Fasting: ≥ 5.5 mmol/L;

• 2 hour following 75 g glucose load: ≥ 8.0 mmol/L.

WHO criteria used for diagnosis of type 2 diabetes and impaired glucose tolerance:

• Type 2 diabetes: Fasting: ≥ 7 mmol/L or 2 hours following 75 g glucose load: ≥ 11.1 mmol/L;

• Impaired glucose tolerance: Fasting: < 7.0 mmol/L and 2 hours following 75 g glucose load: ≥ 7.8 and < 11.1 mmol/L;

• Impaired fasting glucose: Fasting: 6.1 to 6.9 mmol/L and (if measured) 2 hours: < 7.8 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Described as "the enrolled subjects were centrally randomised to study diet by computer generated random numbers, stratified by BMI and weeks of gestation".

Allocation concealment (selection bias)

Low risk

Described as "the allocation sequence was unpredictable and concealed from the recruiter".

Blinding of participants and personnel (performance bias)
All outcomes

Low risk

Reported that (besides research dietitian who provided trial intervention) all study personnel and women were blinded to dietary assignment.

Blinding of outcome assessment (detection bias)
All outcomes

High risk

Un‐blinded research dietitian was responsible for data collection.

Incomplete outcome data (attrition bias)
All outcomes

High risk

In the low‐GI diet group, 1 woman was excluded due to incorrect GDM diagnosis, 3 women withdrew after intervention, 2 women had preterm births, leaving 44 women who completed the study, and 47 women were included in analyses.

In high‐fibre moderate‐GI diet group, 2 women withdrew after group allocation, another 2 women withdrew after intervention; 2 women had preterm births, leaving 43 women who completed the study and 45 women who were included in analyses.

Only 58 of the 99 women randomised and their babies participated the 3‐month follow‐up.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

High risk

At baseline, 2‐hour post 75 g glucose load blood glucose concentrations for women in low‐GI group were significantly higher than those in high‐fibre moderate‐GI group (mean (SD): low‐GI group 8.6 (1.2) mmol/L versus high‐fibre moderate GI group 8.0 (1.3) mmol/L; P = 0.024).

Methods

Randomised controlled trial.

Participants

95 women.

Inclusion criteria: women who were residents of Guangzhow, aged between 18 and 40 years, with GDM diagnosed at 24 to 26 weeks' gestation (see notes).

Exclusion criteria: pre‐pregnancy diabetes; multiple gestation; other severe diseases (hypertension, chronic hepatic and kidney disease and cancer); use of insulin or hypoglycaemic medications; less than 9 years of formal schooling; previous intensive nutrition education or intervention for diabetes.

Setting: China.

Interventions

Low‐moderate GI diet (n = 47 randomised; 41 analysed)

The exchange lists provided contained low‐GL foods.

Moderate‐high GI diet (n = 48 randomised; 42 analysed)

The exchange lists comprised intermediate to high‐GL foods (typical Guangzhou diet).

All women:

• All women received a 1‐on‐1 general dietary intervention every 2 weeks according to the guidelines recommended by the Chinese Medical Association from 24 to 26 weeks until birth, which was usually 12 to 14 weeks later.

• The general dietary intervention was made via detailed advice and the provision of sample daily menus that mainly targeted limitations on starches and fat and encouraged appropriate macronutrient proportion ranges.

• The recommended daily energy intake was approximately 146 kJ (35 kcal)/kg per day for individuals with a normal weight and 104 kJ (25 kcal)/kg per day for obese women (BMI ≥ 28 kg/m²) according to their pre‐pregnancy weight.

• The percentages of energy from carbohydrate, protein and fat were controlled to 45% to 50%, 20% to 24% and 25% to 30%, respectively.

• 5 to 6 meals daily with smaller portions were recommended.

• In addition to general dietary advice, women received instruction on the glycaemic effects of food.

• The exchange lists for both groups designed based on the key foods strategy, including milk products, starchy vegetables and fruits.

• Each participant received 1 copy of Dietary Guidance Handbook for GDM Women. The handbooks for the 2 groups had the same cover, format and length but contained different exchange lists on food GL.

• Dietitians assessed dietary intakes using a 3 day recall to assess the compliance once every 2 weeks and reinforced the intervention at each visit.

• The exact content of the intervention was altered to meet individual needs, based on dietary details and weight gain between the 2 interventions.

• All women were asked not to consume alcohol or dietary supplements or medications that could influence glucose tolerance and lipid metabolism and were told to maintain their usual exercise patterns during the trial.

Outcomes

Data in meta‐analyses for: hypertensive disorders of pregnancy (severe hypertension or pre‐eclampsia; eclampsia); preterm birth; macrosomia; birthweight; postpartum haemorrhage; postpartum infection; gestational weight gain; use of additional pharmacotherapy; glycaemic control (end of intervention fasting and 2‐hour postprandial glucose, and HbA1c).

Notes

Women were screened with a 50 g OGCT according to guidelines of the Chinese Medical Association and the ADA; positive cases (glucose ≥ 7.8 mmol/L following OGCT) were confirmed by further evaluation with a 3‐hour 75 g OGTT, and were diagnosed if they met at least 2 of the following:

• Fasting: > 5.8 mmol/L;

• 1 hour: > 10.6 mmol/L;

• 2 hour: > 9.2 mmol/L,

• 3 hour: > 8.1 mmol/L

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Random numbers were generated by Excel software.

Allocation concealment (selection bias)

High risk

Discussion: "We did not use allocation concealment."

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Discussion: "Both the researchers (the dietitians) and the participants could not be blinded to group status."

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

Not detailed.

Incomplete outcome data (attrition bias)
All outcomes

Unclear risk

"A modified intention‐to‐treat principle including all participants who completed the baseline and follow‐up assessments was used in the analysis." 6 women from the low‐moderate GI group were excluded from the analyses (protocol violation: 3; insulin treatment: 1; pre‐eclampsia: 1; declined: 1); 6 women from the moderate‐high GI group were excluded from the analyses (protocol violation: 3; insulin treatment: 2; severe hypertension: 1).

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

Low risk

No other obvious sources of bias.

Methods

Randomised controlled trial.

Participants

12 women.

Inclusion criteria: obese women (defined as: pre‐pregnancy weight > 120% of ideal body weight as specified by the Corrected 1959 Metropolitan Life Insurance table) with GDM (see notes).

Exclusion criteria: not reported.

Setting: the USA.

Interventions

During the second hospitalised week:

Energy‐restricted diet (n = 7)

Energy‐restricted diet of 1200 kcal/day diet by reducing serving size without changing the pattern and content of the diet in the first hospitalised week.

No energy‐restricted diet (n = 5)

Continued the standard diet prescribed as the first week, for about 2400 kcal/day.

All women: hospitalised for the 2 weeks duration. Studies and diet during the first week were identical for all patients.

During the first hospitalised week:

• Dietary pattern: 25% total energy for breakfast, lunch and dinner; 12.5% total energy for afternoon tea and supper;

• Diet contents: 50% carbohydrate, 30% fat, 20% protein, with 11 g of total dietary fibre per 500 kcal;

• Daily morning double‐voided urine sample for ketone and fasting plasma glucose;

• On the sixth day of each week: blood after overnight fast for plasma glucose, insulin, triglyceride, free fatty acids, glycerol, β‐hydroxhbutyrate. A glucose profile with 25 samples drawn over 24 hrs was initiated as well on the same day;

• On the seventh day of each week: repeat fasting blood work as day 6 and a‐ 3‐hour 100 g OGTT.

Outcomes

Data in meta‐analyses for: insulin sensitivity (during and end of intervention fasting insulin); glycaemic control (during and end of intervention fasting and 24‐hour plasma glucose).

Notes

Carpenter and Coustan's criteria used for GDM diagnosis: 2 or more values meeting the following in 100 g 3‐hour OGTT;

• Fasting: 5.3 mmol/L;

• 1 hour: 10 mmol/L;

• 2 hour: 8.6 mmol/L;

• 3 hour: 7.8 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Described as "subjects were randomised to the control or calorie‐restricted group".

Allocation concealment (selection bias)

Unclear risk

No information was given on allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes

Unclear risk

No information on whether women or research personnel were blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No loss to follow‐up or post‐randomisation exclusions reported.

Selective reporting (reporting bias)

Unclear risk

No clinical outcomes were reported (data available regarding insulin sensitivity and glycaemic control only). No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

152 women randomised.

Inclusion criteria: women aged 18 to 45 years, diagnosed with GDM (see notes) with singleton pregnancies and a gestational age ≤ 35 weeks.

Exclusion criteria: women who were unwilling to follow a prescribed diet, unable to understand Spanish, pregnancy co‐morbidities other than obesity, hypertension, and/or dyslipidaemia.

Setting: Spain

Interventions

Low‐carbohydrate diet (n = 76 randomised; 75 analysed)

• Carbohydrate: 40% of total daily calorie amount.

• Fat: 40% of total daily calorie amount (mainly by increased olive oil intake).

• Protein: 20% of total daily calorie amount.

High‐carbohydrate diet (n = 76 randomised; 75 analysed)

• Carbohydrate: 55% of total daily calorie amount.

• Fat: 25% of total daily calorie amount.

• Protein: 20% of total daily calorie amount.

For both groups: energy content of the diet for each patient was calculated on the basis of pre‐gestational weight with a minimum of 1800 kcal/day.

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; perinatal mortality; hypertensive disorders of pregnancy (hypertension); caesarean section; stillbirth; gestational age at birth; macrosomia; small‐for‐gestational age; neonatal hypoglycaemia; gestational weight gain; use of additional pharmacotherapy.

Notes

Screening and diagnosis of GDM based on the 2006 National Diabetes and Pregnancy clinical guidelines.

All women were screened for GDM at 24 to 28 weeks with 50 g OGCT.

If OGCT ≥ 7.8 mmol/L, they underwent an OGTT; diagnostic criteria were based on the National Diabetes Data Group criteria: 2 or more values met or exceeded the following in 100 g 3‐hour OGTT;

• Fasting: 5.8 mmol/L;

• 1 hour: 10.6 mmol/L;

• 2 hour: 9.2 mmol/L;

• 3 hour: 8.1 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Described as "group allocation was performed using a sealed envelope".

Allocation concealment (selection bias)

Unclear risk

As above; no further details provided.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Described as "two‐arm, open, parallel, randomised controlled trial".

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Unclear risk

Post‐randomisation exclusion:

• Low‐carbohydrate diet (n = 1): due to major violation of the eligibility criteria (twin pregnancy).

• High‐carbohydrate diet (n = 1): withdrew before receiving control diet.

Although intention‐to‐treat principles were employed in the analyses (including those women who discontinued the intervention), a considerable number of women discontinued their allocated diet during the study period, and more women in the high‐carbohydrate diet group discontinued their diet.

Discontinued intervention:

• Low‐carbohydrate diet (n = 5): 3 did not want to continue, 2 for major deviation from the protocol.

• High‐carbohydrate diet (n = 15): 6 did not want to continue, 9 for major deviation from the protocol

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

63 women.

Inclusion criteria: women aged at 18 to 40 years diagnosed with GDM (see notes), with a singleton pregnancy, no previous GDM, non‐smokers, and seen for the first dietary visit between 28 and 32 weeks' gestation, with an ability to follow the protocol requirements.

Exclusion criteria: any condition or medication that could affect glucose concentrations and unwillingness to follow the prescribed diet.

Setting: Australia.

Interventions

Low‐moderate GI diet (n = 31)

Diet based on previously verified low–GI food, including pasta, grain breads, and unprocessed breakfast cereals with a high‐fibre content. Women were specifically asked to avoid consuming white bread, processed commercial breakfast cereals, potatoes, and some rice varieties.

Moderate‐high GI diet (n = 32)

Women were advised to follow a diet with a high‐fibre and low‐sugar content, with no specific mention of the GI. Potatoes, whole wheat bread, and specific high‐fibre, moderate‐to‐high GI breakfast cereals were recommended.

All women:

• were provided with a home glucose meter and were asked to test fasting and 1 hour after the start of each of their 3 major meals at least every second day;

• had at least 4 diabetes centre visits with a dietitian for dietary assessment; if they required insulin they were seen as many times as necessary for insulin adjustment;

• were provided with a booklet outlining the carbohydrate choices the carbohydrate food amounts constituting 1 serving (based on 15 g portions);

• were advised to consume 3 small meals and 2 to 3 snacks with a specified number of servings of carbohydrate.

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; caesarean section; gestational age at birth; preterm birth; macrosomia; small‐for‐gestational age; birthweight; head circumference at birth; length at birth; ponderal index at birth; normal vaginal birth; operative vaginal birth; induction of labour; use of additional pharmacotherapy.

Notes

ADIPS criteria used for GDM diagnosis: 1 or more value met or exceeded:

• Fasting: ≥ 5.5 mmol/L;

• 2 hour after 75 g glucose load: ≥ 8.0 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Described as: "participants were randomly assigned to receive one of two different diets using permuted blocks of unequal size with the list generated using STATA (Version 7.0)".

Allocation concealment (selection bias)

Unclear risk

Described as above; unclear methods for allocation concealment.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Women and study dietitian were not blinded. The physician caring for the women was blinded to group allocation.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No loss to follow‐up or post‐randomisation exclusion.

Selective reporting (reporting bias)

Unclear risk

Data reported incompletely for some outcomes in the manuscript; "There were no significant differences between the women in either group with respect to weight gain from baseline to delivery, induction of labor, method of delivery, or gestational age at delivery (data not shown)." Trial authors provided additional unpublished data.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

125 women.

Inclusion criteria: women at ≤ 35 weeks and 6 days gestation; > 110% of ideal body weight for height (adjusted for expected pregnancy weight gain and using a BMI of 25 as equal to 100% ideal body weight); diagnosed with GDM (see notes).

Exclusion criteria: not reported.

Setting: Australia.

Interventions

Energy‐restricted diet (n = 67 randomised; 63 analysed)

Women were placed on a diabetic diet providing between 6800 and 7600 kJ energy per day, which represented 70% of the Recommended Dietary Intake for pregnant women (30% energy restriction).

No energy‐restricted diet (n = 58 randomised; 54 analysed):

Women were placed on diabetic diet without energy restriction, providing 8600 to 9500 kJ energy per day.

All women:

• diabetes education provided by a research dietitian at each antenatal visit;

• hyperglycaemia control, blood glucose self‐monitoring: before and 2 hours after each meal (6 times per day), for a minimum of 2 days each week;

• fetal and maternal surveillance and anticipated term birth;

• use of insulin decided by medical staff that were blinded to group allocation. Criteria for insulin: fasting blood glucose > 5.5 mmol/L or 2‐hour: > 7.0 mmol/L on 2 or more occasions in any 72‐hour period at the same pre‐ or postprandial epoch;

• metabolic monitoring for HbA1c, serum beta‐hydroxybutyrate, urinary ketone;

• 3‐day food intake diaries for adherence to diet.

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; caesarean section; gestational age at birth; preterm birth; macrosomia; small‐for‐gestational age; birthweight; head circumference at birth; length at birth; ponderal index at birth; normal vaginal birth; operative vaginal birth; induction of labour; use of additional pharmacotherapy.

Notes

7 sets of twins were included in the study, 3 sets in the energy‐restricted diet group and 4 sets in the no energy‐restricted diet group.

GDM diagnosed if:

• fasting blood glucose > 5.4 mmol/L and/or 2‐hour blood glucose > 7.9 mmol/L in 75 g 2‐hour OGTT.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Described as "women were allocated at random by draw of opaque numbered envelopes".

Allocation concealment (selection bias)

Unclear risk

Described as above.

Blinding of participants and personnel (performance bias)
All outcomes

Low risk

Women and diabetes service staff were blinded to allocation to diet group.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

Described as that "demographic, obstetric and neonatal data were collected prospectively". No information on whether or not outcome assessors were able to be blinded to group allocation.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

A total of 8 women (4 from each group) withdrew and were excluded from data analysis; reasons for withdrawal and baseline details about these 8 women were not given. Some data points have small numbers of lost women that are unexplained in the text; this was considered unlikely to have affected the overall outcomes. 

Selective reporting (reporting bias)

High risk

A number of outcomes for the neonate were reported incompletely and thus data could not be used in a meta‐analysis: e.g. SE not reported for birthweight in energy‐restricted diet group; and "The mean maximum bilirubin level measured in the two groups was the same." No access to study protocol to further assess the risk of selective reporting.

Other bias

High risk

"The reported maternal medical and obstetric histories were similar in the two groups except for a significantly higher proportion of women with a history of preterm labour in the control group."

Methods

Randomised controlled trial.

Participants

22 women. A total of 50 women were involved in the trial, but only 22 women were diagnosed with GDM and provided outcome data for this review.

Inclusion criteria: women diagnosed with GDM (see notes) between 24 and 29 weeks' gestation.

Exclusion criteria: diagnosis of GDM after 29 weeks' gestation.

Setting: United States.

Interventions

High‐fibre diet (n = 11)

Diet containing 80 g fibre per day; 20% daily energy intake derived from fat, and 60% derived from carbohydrate.

Standard‐fibre diet (n = 11)

ADA diet; diet containing 20 g fibre per day; 30% daily energy intake derived from fat, and 50% derived from carbohydrate.

All women:

Capillary blood glucose assessments 6 times a day (before and after each meal), twice weekly.

Outcomes

Data in meta‐analyses for: gestational age at birth; birthweight; gestational weight gain; use of additional pharmacotherapy; glycaemic control (mean blood glucose); maternal hypoglycaemia.

Notes

GDM diagnostic criteria not reported.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Low risk

Randomisation was done using a random numbers table.

Allocation concealment (selection bias)

Unclear risk

Detail regarding allocation concealment was not reported.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Women were unlikely to have been blinded. The research dietitian and the diabetes nurse specialist who were responsible for monitoring diet compliance and glycaemic control were unlikely to have been blinded. Unclear whether other research personnel were able to be blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Unclear risk

Women with insulin‐dependent diabetes and GDM were included in the trial. It was reported that 11 women (5 in the standard‐fibre diet group and 6 in the high‐fibre diet) were excluded from the study after randomisation: 1 had a spontaneous abortion, 2 moved away, and 4 from each group were noncompliant. It is unclear how many of these 11 women excluded after randomisation were women with GDM.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

20 women.

Inclusion criteria: pregnant immigrant women with GDM (see notes).

Exclusion criteria: not reported.

Setting: Italy.

Interventions

Ethnic‐specific diet (n = 10)

• Typical foods of the women's home countries, identified using a photographic atlas (Dietmeter and Photographic Atlas, Scotti Bassani) were included.

• Foods that commonly consumed by patients according to their ethnicity were included.

• Dishes were broken down into the various ingredients, shown raw and cooked.

• Due to difficulties in using kitchen scales, measures such as cups, or spoonfuls handfuls or pinches, were preferred.

• The food pyramids of the specific country of origin were used.

Standard healthy diet (n = 10)

• Meal plan according to the ADA guidelines for GDM.

All women

• The 2 meal plans had the same nutrient composition (standard meal plan: carbohydrate: 53%, fat: 28%, protein: 18%, fibre: 26 g; ethnic meal plan: carbohydrate: 55%, fat: 28%, protein: 17%, fibre: 21 g), and energy intake was from 1800 to 2200 Kcal, depending on pre‐pregnancy BMI.

• Before a meal plan was developed, women had a dietary assessment to determine whether their intakes of essential nutrients were adequate, whether they were eating excessively, and to identify foods avoided, as well as food intolerances or allergies.

• Food models, using measures in cups, glasses, and bowls, were used to teach women about appropriate serving sizes.

• All women were monitored to achieve good metabolic control: fasting plasma glucose < 5.3 mmol/L and 1‐hour postprandial plasma glucose < 7.2 mmol/L. The women on diet treatment performed 2 measurements per day (fasting and 1‐hour postprandial glucose on alternate meals over the course of a week). The women on insulin therapy performed 4 measurements per day (fasting and 1 hour after breakfast, lunch, and dinner).

• Women saw a specialist every 2 weeks. Insulin treatment was started when fasting glucose and/or 1‐hour postprandial glucose exceeded the above concentrations in more than 1 measurement.

• All GDM women were followed up for metabolic and obstetric purposes until birth.

Outcomes

Data in meta‐analyses for: large‐for‐gestational age; neonatal composite outcome; hypertensive disorders of pregnancy (gestational hypertension); caesarean section; gestational age at birth; macrosomia; small‐for‐gestational age; birthweight; respiratory distress syndrome; neonatal hypoglycaemia; hyperbilirubinaemia; hypocalcaemia; gestational weight gain; adherence to intervention; use of additional pharmacotherapy.

Notes

Screening for GDM was done with a OGCT between weeks 24 and 28 of gestation, and the diagnosis was confirmed with a 100 g OGTT as recommended by the 4th International Workshop Conference on GDM: GDM diagnosed when ≥ 2 values were met or exceeded:

• Fasting: 5.3mmol/L;

• 1 hour: 10.0 mmol/L;

• 2 hour: 8.6 mmol/L;

• 3 hour: 7.8 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Described as "the women enrolled were randomly assigned to two groups".

Allocation concealment (selection bias)

Unclear risk

As above.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Women and dietitian were unlikely to have been blinded. Unclear whether other research personnel were able to be blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No loss to follow‐up or post‐randomisation exclusion.

Selective reporting (reporting bias)

High risk

Metabolic outcomes reported in Figures, with no variance measures reported; therefore unable to be included in meta‐analyses. No access to study protocol; therefore unable to further assess the risk of selective reporting.

Other bias

Low risk

No other obvious risk of bias.

Methods

Randomised controlled trial.

Participants

84 women.

Inclusion criteria: women diagnosed with GDM (see notes), aged 22 to 38 years and between 24 and 28 weeks' gestation; residents of Changzhou and only performed light physical activity (such as type writing, 6 hours per day); did not have pregnancy‐related complications and had no history of diabetes, hypertension or GDM; willingness to accept dietary intervention, cook and dine out.

Exclusion criteria: not reported.

Setting: China.

Interventions

High unsaturated fat diet (n = 41)

Carbohydrates accounted for 50% to 54% of the total energy; fat accounted for 31% to 35% of the total energy; sunflower oil (45 g to 50 g daily) was used as cooking oil.

Low unsaturated fat diet (n = 43)

Carbohydrates accounted for 55% to 60% of the total energy; fat accounted for 25% to 30% of the total energy, sunflower oil (20 g daily) was used as cooking oil.

All women

• All women received an oil control pot to control the amount of cooking oil used.

• Special nurses performed weekly follow‐up by telephone to assess the women's diets, and 24‐hour dietary surveys were conducted in person every 4 weeks. Women were also asked to keep daily food diaries to ensure adherence.

• Women's total daily calorie requirements were calculated according to height, weight, gestational weeks, and physical strength. The total caloric intake of a light physical worker in late pregnancy was calculated as: ideal weight × 30 kcal/ kg· day + 200 kcal. Protein accounted for 15% to 20% of the total energy (i.e., energy supply percentage) in order to maintain total energy and protein intake.

• Breakfast, snacks, lunch, snacks, dinner, and snacks composed 20%, 5%, 35%, 5%, 30%, and 5% of the total daily energy intake, respectively.

• All women received individualised dietary guidance from a nutritionist after being diagnosed with GDM.

• All women completed a 24‐hour dietary survey for the past 3 days at 24 to 28 weeks' gestation; food weight models were introduced before the survey.

Outcomes

Data in meta‐analyses for: gestational age at birth; preterm birth; macrosomia; birthweight; gestational weight gain; insulin sensitivity (end of intervention IAI); use of additional pharmacotherapy; glycaemic control (end of intervention fasting and 2‐hour postprandial glucose).

Notes

GDM diagnosis was based on 75 g OGTT at 24 to 28 weeks' gestation. The IADPSG diagnostic criteria used for GDM diagnosis: if the glucose concentration exceeded any of:

• Fasting: 5.1 mmol/L;

• 1 hour: 10.0 mmol/L;

• 2 hour: 8.5 mmol/L.

Risk of bias

Bias

Authors' judgement

Support for judgement

Random sequence generation (selection bias)

Unclear risk

Described as "they were randomly divided into 2 groups: 41 and 43 patients were included in the experimental and control groups, respectively."

Allocation concealment (selection bias)

Unclear risk

As above.

Blinding of participants and personnel (performance bias)
All outcomes

High risk

Women and the nutritionist were unlikely to have been blinded. Unclear whether other research personnel were able to be blinded or not.

Blinding of outcome assessment (detection bias)
All outcomes

Unclear risk

No information on whether outcome assessors were blinded.

Incomplete outcome data (attrition bias)
All outcomes

Low risk

No loss to follow‐up or post‐randomisation exclusion.

Selective reporting (reporting bias)

Unclear risk

No access to study protocol; therefore not able to confidently assess the risk of selective reporting.

Other bias

Low risk

No other obvious risk of bias.