There are some differences between our published protocol (Brown 2015) and the full review.

The title was listed as Myo‐inositol for preventing gestational diabetes in our published protocol but we have edited this to Antenatal dietary supplementation with myo‐inositol in women during pregnancy for preventing gestational diabetes in order to allow more clarity around the intervention, population and outcome.

Methods/Criteria for considering studies for this review

Types of interventions: we have expanded this section to include myo‐inositol in a combination preparation; this is also reflected in our list of planned subgroup analyses.

Types of participants: we have clarified that participants will be pregnant women rather than pregnant women at risk of gestational diabetes mellitus (GDM).

We have incorporated the use of GRADE to assess the quality of the body of evidence and have included 'Summary of findings' tables; this was not pre‐specified in our published protocol.

We have reported on the outcome 'need for supplementary insulin therapy' ‐ whilst this is not listed in our methods/outcomes section (and was not pre‐specified in our published protocol), we report on this outcome for interest.

Following a consultative process with Professor Caroline Crowther, Dr Julie Brown, Dr Philippa Middleton, Emily Bain and Tineke Crawford, a core set of primary and secondary outcomes for GDM systematic reviews and core outcomes for GRADE assessment for GDM systematic reviews were drawn up. This has resulted in a number of changes detailed below. These core outcomes were agreed upon after this review had been submitted for peer review.

Additionally, as this is a review on the use of a dietary supplement as an intervention, adverse effects of the intervention has been added as an outcome.

Previous maternal primary outcomes listed in protocol

1. Incidence of gestational diabetes mellitus (GDM) (diagnostic criteria as defined in individual trials)

2. Pre‐eclampsia

3. Caesarean section

Updated maternal primary outcomes used in review

1. Gestational diabetes mellitus (GDM)

2. Hypertensive disorders of pregnancy (including pre‐eclampsia, eclampsia, pregnancy‐induced hypertension)

Previous neonatal primary outcomes listed in protocol

1. Large‐for‐gestational age (birthweight greater than the 90th centile; or as defined by individual trial)

2. Perinatal mortality

3. Death or morbidity composite (variously defined by trials, e.g. infant death, shoulder dystocia, bone fracture or nerve palsy)

Updated neonatal primary outcomes used in review

1. Large‐for‐gestational age (birthweight greater than the 90th centile; or as defined by individual trial)

2. Perinatal mortality (stillbirth and neonatal mortality)

3. Mortality or morbidity composite (variously defined by trials, e.g. infant death, shoulder dystocia, bone fracture or nerve palsy)

Previous maternal secondary outcomes listed in protocol

1. Postnatal weight retention

2. Body mass index (BMI)

3. Development of type 2 diabetes mellitus

4. Development of type 1 diabetes mellitus

5. Impaired glucose tolerance (as defined in individual trials)

6. Insulin sensitivity (as defined in individual trials)

7. Incidence of pregnancy hyperglycaemia not meeting GDM diagnostic criteria (diagnostic criteria as defined in individual trials)

8. Induction of labour

9. Perineal trauma

10. Weight gain during pregnancy

11. Adiponectin levels

12. Gestational age at screening for GDM

13. Postpartum haemorrhage

14. Postpartum infection

15. Placental abruption

16. Polyhydramnios

17. Compliance with treatment

18. Breastfeeding at discharge, six weeks' postpartum

19. Women’s sense of well‐being and quality of life (as defined in individual trials)

20. Women’s view of intervention

Updated maternal secondary outcomes used in review

1. Caesarean section

2. Placental abruption

3. Induction of labour

4. Perineal trauma

5. Postpartum haemorrhage

6. Postpartum infection

7. Weight gain during pregnancy

8. Adherence to the intervention (as defined by trialists)

9. Behaviour changes associated with the intervention (as defined by trialists)

10. Relevant biomarker changes associated with the intervention (e.g. adiponectin, free fatty acids, triglycerides, high density lipoproteins, low density lipoproteins, insulin)

11. Sense of well‐being and quality of life

12. Views of the intervention

13. Breastfeeding (e.g. at discharge, six weeks postpartum)

14. Adverse effects of intervention

Long‐term maternal outcomes

1. Postnatal depression

2. Postnatal weight retention or return to pre‐pregnancy weight

3. Body mass index (BMI)

4. Gestational diabetes mellitus in a subsequent pregnancy

5. Type I diabetes mellitus

6. Type II diabetes mellitus

7. Impaired glucose tolerance

8. Cardiovascular health (as defined by trialists, including blood pressure (BP), hypertension, cardiovascular disease, metabolic syndrome)

Previous neonatal secondary outcomes listed in protocol

1. Macrosomia (as defined in individual trials)

2. Birthweight and z‐score

3. Head circumference and z‐score

4. Length and z‐score

5. Small‐for‐gestational age (as defined in individual trials)

6. Neonatal hypoglycaemia requiring treatment (as defined in individual trials)

7. Gestational age at birth

8. Preterm birth (less than 37 weeks’ gestational age)

9. Shoulder dystocia

10. Bone fracture

11. Nerve palsy

12. Respiratory distress syndrome

13. Hyperbilirubinaemia requiring treatment (as defined in individual trials)

14. Apgar scores (less than seven at five minutes)

15. Ponderal index

16. Fetal adiposity (as defined in individual trials)

17. Neonatal glucose concentration

18. Infant mortality (fetal, neonatal, perinatal)

Updated secondary outcomes used in review

1. Stillbirth

2. Neonatal mortality

3. Gestational age at birth

4. Preterm birth (less than 37 weeks' gestation and less than 32 weeks' gestation)

5. Apgar score (less than seven at five minutes)

6. Macrosomia

7. Small‐for‐gestational age

8. Birthweight and z‐score

9. Head circumference and z‐score

10. Length and z‐score

11. Ponderal index

12. Adiposity

13. Shoulder dystocia

14. Bone fracture

15. Nerve palsy

16. Respiratory distress syndrome

17. Hypoglycaemia (variously defined)

18. Hyperbilirubinaemia

Previous childhood outcomes listed in protocol

1. Weight

2. Height

3. Head circumference

4. Body mass index

5. Adiposity (fat mass/fat free mass (variously measured))

6. Blood pressure

7. Impaired glucose tolerance (as defined in individual trials)

8. Development of type 1 diabetes mellitus

9. Development of type 2 diabetes mellitus

10. Insulin sensitivity

11. Dyslipidaemia or metabolic syndrome

12. Neurodisability

13. Educational achievement

Updated childhood outcomes used in review

1. Weight and z scores

2. Height and z scores

3. Head circumference and z scores

4. Adiposity (e.g. as measured by BMI, skinfold thickness)

5. Blood pressure

6. Type I diabetes mellitus

7. Type II diabetes mellitus

8. Impaired glucose tolerance

9. Dyslipidaemia or metabolic syndrome

10. Neurodisability

11. Educational achievement

Previous adulthood outcomes listed in protocol

1. Weight

2. Height

3. BMI

4. Adiposity (fat mass/fat‐free mass (variously measured))

5. Blood pressure

6. Impaired glucose tolerance (as defined in individual trials)

7. Development of type 1 diabetes

8. Development of type 2 diabetes

9. Insulin sensitivity (as defined in individual trials)

10. Dyslipidaemia or metabolic syndrome

11. Educational achievement

Updated adulthood outcomes used in review

1. Weight

2. Height

3. Adiposity (e.g. as measured by BMI, skinfold thickness)

4. Cardiovascular health (as defined by trialists, including BP, hypertension, cardiovascular disease, metabolic syndrome)

5. Type I diabetes mellitus

6. Type II diabetes mellitus

7. Impaired glucose tolerance

8. Dyslipidaemia or metabolic syndrome

9. Employment, education and social status/achievement

Previous health services cost outcomes listed in protocol

1. Number of hospital visits or health professional visits (e.g. midwife, obstetrician, physician, dietitian)

2. Antenatal visits for mother

3. Direct costs to families in relation to the management provided

4. Length of postnatal stay (mother)

5. Admission to neonatal ward/ neonatal intensive care unit

6. Length of postnatal stay (baby)

7. Cost of maternal care

8. Cost of offspring care

Updated health services cost outcomes used in review

1. Number of hospital or health professional visits (e.g. midwife, obstetrician, physician, dietitian, diabetic nurse)

2. Number of antenatal visits or admissions

3. Length of antenatal stay

4. Neonatal intensive care unit admission

5. Length of postnatal stay (mother)

6. Length of postnatal stay (baby)

7. Costs to families associated with the management provided

8. Costs associated with the intervention

9. Cost of maternal care

10. Cost of offspring care

Previous GRADE outcomes listed in protocol

1. Incidence of GDM (diagnostic criteria as defined in individual trials)

2. Pre‐eclampsia

3. Mode of birth

4. Large‐for‐gestational age (birthweight greater than the 90th centile; or as defined by individual trial)

5. Perinatal mortality

6. Fetal adiposity

7. Impaired glucose tolerance as child/adult

Updated GRADE outcomes used in review

Maternal

1. Diagnosis of GDM

2. Gestational weight gain

3. Hypertensive disorders of pregnancy (including pre‐eclampsia, eclampsia, pregnancy‐induced hypertension)

4. Caesarean Section

5. Perineal trauma

6. Postnatal depression

7. Development of subsequent type II diabetes mellitus

Offspring (infant, child, adult)

1. Large‐for‐gestational age

2. Perinatal mortality (stillbirth and neonatal mortality)

3. Composite of serious neonatal outcomes

4. Neonatal hypoglycaemia (variously defined)

5. Offspring adiposity (e.g. as measured by BMI, skinfold thickness)

6. Offspring diabetes

7. Neurosensory disability