Aromatase inhibitors (letrozole) for ovulation induction in infertile women with polycystic ovary syndrome

Sebastian Franik; Quang-Khoi Le; Jan AM Kremer; Ludwig Kiesel; Cindy Farquhar

doi:10.1002/14651858.CD010287.pub4

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Figure 1

Study flow diagram for update 2021

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Figure 2

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

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Figure 3

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

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Figure 4

Forest plot of comparison: 2 Aromatase inhibitors compared to selective oestrogen receptor modulators (SERMs), outcome: 2.1 Live birth rate.

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Figure 5

Funnel plot of comparison: 2 AIs compared to SERMs with or without adjuncts, followed by timed intercourse, outcome: 2.1 Live birth rate.

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Figure 6

Forest plot of comparison: 2 Aromatase inhibitors compared to selective oestrogen receptor modulators SERMs, outcome: 2.6 Ovarian hyperstimulation syndrome rate.

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Figure 7

Forest plot of comparison: 2 Aromatase inhibitors compared to selective oestrogen receptor modulators SERMs, outcome: 2.5 Multiple pregnancy rate.

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Analysis 1.1

Comparison 1: Letrozole compared to placebo, Outcome 1: Live birth rate

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Analysis 1.2

Comparison 1: Letrozole compared to placebo, Outcome 2: Ovarian hyperstimulation syndrome rate

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Analysis 1.3

Comparison 1: Letrozole compared to placebo, Outcome 3: Clinical pregnancy rate

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Analysis 1.4

Comparison 1: Letrozole compared to placebo, Outcome 4: Miscarriage rate per woman

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Analysis 1.5

Comparison 1: Letrozole compared to placebo, Outcome 5: Miscarriage rate per pregnancy

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Analysis 1.6

Comparison 1: Letrozole compared to placebo, Outcome 6: Multiple pregnancy rate

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Analysis 2.1

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 1: Live birth rate

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Analysis 2.2

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 2: Live birth rate by BMI

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Analysis 2.3

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 3: Live birth rate by first‐ or second‐line treatment

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Analysis 2.4

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 4: Impact of allocation bias for live birth rate

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Analysis 2.5

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 5: Impact of detection bias for live birth rate

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Analysis 2.6

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 6: Impact of attrition bias for live birth rate

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Analysis 2.7

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 7: Ovarian hyperstimulation syndrome rate

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Analysis 2.8

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 8: Ovarian hyperstimulation syndrome rate by BMI

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Analysis 2.9

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 9: Clinical pregnancy rate

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Analysis 2.10

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 10: Impact of allocation bias for clinical pregnancy rate

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Analysis 2.11

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 11: Miscarriage rate per woman

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Analysis 2.12

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 12: Miscarriage rate per pregnancy

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Analysis 2.13

Comparison 2: Letrozole compared to SERM with or without adjuncts, followed by timed intercourse, Outcome 13: Multiple pregnancy rate

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Analysis 3.1

Comparison 3: Letrozole compared to SERMs with our without adjuncts, followed by IUI, Outcome 1: Ovarian hyperstimulation syndrome rate

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Analysis 3.2

Comparison 3: Letrozole compared to SERMs with our without adjuncts, followed by IUI, Outcome 2: Clinical pregnancy rate

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Analysis 3.3

Comparison 3: Letrozole compared to SERMs with our without adjuncts, followed by IUI, Outcome 3: Miscarriage rate per woman

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Analysis 3.4

Comparison 3: Letrozole compared to SERMs with our without adjuncts, followed by IUI, Outcome 4: Miscarriage rate per pregnancy

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Analysis 3.5

Comparison 3: Letrozole compared to SERMs with our without adjuncts, followed by IUI, Outcome 5: Multiple pregnancy rate

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Analysis 4.1

Comparison 4: Letrozole compared to laparoscopic ovarian drilling, Outcome 1: Live birth rate

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Analysis 4.2

Comparison 4: Letrozole compared to laparoscopic ovarian drilling, Outcome 2: Clinical pregnancy rate

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Analysis 4.3

Comparison 4: Letrozole compared to laparoscopic ovarian drilling, Outcome 3: Miscarriage rate per woman

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Analysis 4.4

Comparison 4: Letrozole compared to laparoscopic ovarian drilling, Outcome 4: Miscarriage rate per pregnancy

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Analysis 4.5

Comparison 4: Letrozole compared to laparoscopic ovarian drilling, Outcome 5: Multiple pregnancy rate

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Analysis 5.1

Comparison 5: Letrozole compared to FSH, Outcome 1: Live birth

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Analysis 5.2

Comparison 5: Letrozole compared to FSH, Outcome 2: Ovarian hyperstimulation syndrome rate

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Analysis 5.3

Comparison 5: Letrozole compared to FSH, Outcome 3: Clinical pregnancy rate

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Analysis 5.4

Comparison 5: Letrozole compared to FSH, Outcome 4: Miscarriage rate per woman

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Analysis 5.5

Comparison 5: Letrozole compared to FSH, Outcome 5: Miscarriage rate per pregnancy

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Analysis 5.6

Comparison 5: Letrozole compared to FSH, Outcome 6: Multiple pregnancy rate

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Analysis 6.1

Comparison 6: Letrozole compared to anastrozole, Outcome 1: Clinical pregnancy rate

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Analysis 6.2

Comparison 6: Letrozole compared to anastrozole, Outcome 2: Multiple pregnancy rate

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Analysis 7.1

Comparison 7: Letrozole compared to berberine, followed by timed intercourse, Outcome 1: Live birth rate

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Analysis 7.2

Comparison 7: Letrozole compared to berberine, followed by timed intercourse, Outcome 2: Clinical pregnancy rate

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Analysis 7.3

Comparison 7: Letrozole compared to berberine, followed by timed intercourse, Outcome 3: Miscarriage rate per woman

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Analysis 7.4

Comparison 7: Letrozole compared to berberine, followed by timed intercourse, Outcome 4: Miscarriage rate per pregnancy

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Analysis 7.5

Comparison 7: Letrozole compared to berberine, followed by timed intercourse, Outcome 5: Multiple pregnancy rate

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Analysis 8.1

Comparison 8: Different administration protocols of letrozole, Outcome 1: Clinical pregnancy rate

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Analysis 9.1

Comparison 9: Dosage studies of letrozole, Outcome 1: Ovarian hyperstimulation syndrome rate

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Analysis 9.2

Comparison 9: Dosage studies of letrozole, Outcome 2: Clinical pregnancy rate

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Analysis 9.3

Comparison 9: Dosage studies of letrozole, Outcome 3: Miscarriage rate per woman

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Analysis 9.4

Comparison 9: Dosage studies of letrozole, Outcome 4: Miscarriage rate per pregnancy

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Analysis 9.5

Comparison 9: Dosage studies of letrozole, Outcome 5: Multiple pregnancy rate

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Summary of findings 1. Letrozole with or without adjuncts compared to SERMs with or without adjuncts followed by timed intercourse for infertile women with polycystic ovary syndrome

Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect (95% CI)	No. of participants (trials)	Certainty of the evidence (GRADE)	Comments
Letrozole with or without adjuncts compared to SERMs with or without adjuncts followed by timed intercourse for infertile women with polycystic ovary syndrome
Patient or population: infertile women with polycystic ovary syndrome Setting: (fertility) clinics or outpatient settings Intervention: letrozole with or without adjuncts followed by timed intercourse Comparison: SERMs (clomiphene citrate) with or without adjuncts followed by timed intercourse
Outcomes	Risk with SERMs with or without adjuncts	Risk with letrozole with or without adjuncts	Relative effect (95% CI)	No. of participants (trials)	Certainty of the evidence (GRADE)	Comments
Live birth rate	204 per 1000	307 per 1000 (265 to 352)	OR 1.72 (1.40 to 2.11)	2060 (11 RCTs)	⊕⊕⊕⊕ High
Ovarian hyperstimulation syndrome rate	7 per 1000	5 per 1000 (5 to 5)	RD −0.00 (−0.01 to 0.01)	1848 (10 RCTs)	⊕⊕⊕⊕ High
Clinical pregnancy rate	242 per 1000	350 per 1000 (316 to 387)	OR 1.69 (1.45 to 1.98)	3321 (23 RCTs)	⊕⊕⊕⊕ High
Miscarriage rate per pregnancy	252 per 1000	240 per 1000 (182 to 307)	OR 0.94 (0.66 to 1.32)	736 (15 RCTs)	⊕⊕⊕⊕ High
Multiple pregnancy rate	22 per 1000	16 per 1000 (9 to 28)	OR 0.74 (0.42 to 1.32)	2247 (14 RCTs)	⊕⊕⊕⊕ High
*The risk in the intervention group (and its 95% confidence interval) is based on the mean risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; OR: odds ratio; RD: risk difference; RCT: randomised controlled trial
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.

Summary of findings 1. Letrozole with or without adjuncts compared to SERMs with or without adjuncts followed by timed intercourse for infertile women with polycystic ovary syndrome

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Summary of findings 2. Letrozole compared to laparoscopic ovarian drilling for infertile women with polycystic ovary syndrome

Outcomes	*Anticipated absolute effects^ (95% CI)**		Relative effect (95% CI)	No. of participants (trials)	Certainty of the evidence (GRADE)	Comments
Letrozole compared to laparoscopic ovarian drilling compared to placebo for infertile women with polycystic ovary syndrome
Patient or population: infertile women with polycystic ovary syndrome Setting: (fertility) clinics or outpatient settings Intervention: letrozole with or without adjuncts followed by timed intercourse Comparison: laparoscopic ovarian drilling (LOD) followed by timed intercourse
Outcomes	Risk with LOD	Risk with letrozole	Relative effect (95% CI)	No. of participants (trials)	Certainty of the evidence (GRADE)	Comments
Live birth rate	229 per 1000	380 per 1000 (227 to 561)	OR 2.07 (0.99 to 4.32)	141 (1 RCT)	⊕⊝⊝⊝ Very Low^a,b,c
Ovarian hyperstimulation syndrome rate	No trials reported on this outcome
Clinical pregnancy rate	290 per 1000	375 per 1000 (279 to 482)	OR 1.47 (0.95 to 2.28)	376 (3 RCTs)	⊕⊕⊝⊝ Low^a,b
Miscarriage rate per pregnancy	151 per 1000	104 per 1000 (38 to 254)	OR 0.65 (0.22 to 1.92)	122 (3 RCTs)	⊕⊕⊝⊝ Low^a,b
Multiple pregnancy rate	0 per 1000	0 per 1000 (0 to 0)	OR 3.00 (0.12 to 74.90)	141 (1 RCT)	⊕⊝⊝⊝ Very Low^a,b,c
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; OR: odds ratio; RCT: randomised controlled trial
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.
^aInsufficient data to allow judgement of risk of bias in some trials ‐ downgraded one level for serious risk of bias. ^bThere is insufficient data to determine if there is a difference as opposed to no evidence of a difference ‐ downgraded one level for imprecision. ^cAnalysis is based on only one trial ‐ downgraded one additional level for imprecision.

Summary of findings 2. Letrozole compared to laparoscopic ovarian drilling for infertile women with polycystic ovary syndrome

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Comparison 1. Letrozole compared to placebo

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Live birth rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

1.2 Ovarian hyperstimulation syndrome rate Show forest plot	2	167	Risk Difference (M‐H, Fixed, 95% CI)	0.00 [‐0.05, 0.05]

1.3 Clinical pregnancy rate Show forest plot	2	167	Odds Ratio (M‐H, Fixed, 95% CI)	2.88 [1.08, 7.66]

1.4 Miscarriage rate per woman Show forest plot	2	167	Odds Ratio (M‐H, Fixed, 95% CI)	1.60 [0.26, 9.89]

1.5 Miscarriage rate per pregnancy Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

1.6 Multiple pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

Comparison 1. Letrozole compared to placebo

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Comparison 2. Letrozole compared to SERM with or without adjuncts, followed by timed intercourse

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Live birth rate Show forest plot	11	2060	Odds Ratio (M‐H, Fixed, 95% CI)	1.72 [1.40, 2.11]

2.1.1 AIs versus clomiphene citrate	8	1646	Odds Ratio (M‐H, Fixed, 95% CI)	1.79 [1.42, 2.25]
2.1.2 Aromatase inhibitor + metformin compared to clomiphene + metformin	2	194	Odds Ratio (M‐H, Fixed, 95% CI)	1.70 [0.89, 3.23]
2.1.3 Aromatase inhibitor + FSH compared to clomiphene + FSH	1	120	Odds Ratio (M‐H, Fixed, 95% CI)	1.18 [0.53, 2.61]
2.1.4 AIs versus clomiphene + estradiol valerate	1	100	Odds Ratio (M‐H, Fixed, 95% CI)	1.48 [0.54, 4.06]
2.2 Live birth rate by BMI Show forest plot	9	1880	Odds Ratio (M‐H, Fixed, 95% CI)	1.74 [1.41, 2.15]

2.2.1 BMI > 25	6	1428	Odds Ratio (M‐H, Fixed, 95% CI)	1.84 [1.44, 2.35]
2.2.2 BMI < 25	3	452	Odds Ratio (M‐H, Fixed, 95% CI)	1.49 [0.98, 2.25]
2.3 Live birth rate by first‐ or second‐line treatment Show forest plot	11		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

2.3.1 No previous ovulation induction	4	1089	Odds Ratio (M‐H, Fixed, 95% CI)	1.61 [1.22, 2.14]
2.3.2 CC‐resistant women	4	344	Odds Ratio (M‐H, Fixed, 95% CI)	1.78 [1.08, 2.93]
2.3.3 Unclear or mixed study cohort	3	627	Odds Ratio (M‐H, Fixed, 95% CI)	1.88 [1.31, 2.69]
2.4 Impact of allocation bias for live birth rate Show forest plot	11		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

2.4.1 Unclear risk of allocation	8	1031	Odds Ratio (M‐H, Fixed, 95% CI)	1.90 [1.42, 2.54]
2.4.2 Low risk of allocation	3	1029	Odds Ratio (M‐H, Fixed, 95% CI)	1.57 [1.18, 2.08]
2.5 Impact of detection bias for live birth rate Show forest plot	11	2060	Odds Ratio (M‐H, Fixed, 95% CI)	1.72 [1.40, 2.11]

2.5.1 High risk of detection	1	64	Odds Ratio (M‐H, Fixed, 95% CI)	2.60 [0.83, 8.13]
2.5.2 Low risk of detection	5	1189	Odds Ratio (M‐H, Fixed, 95% CI)	1.65 [1.26, 2.16]
2.5.3 Unclear risk of detection	5	807	Odds Ratio (M‐H, Fixed, 95% CI)	1.76 [1.27, 2.44]
2.6 Impact of attrition bias for live birth rate Show forest plot	11		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

2.6.1 Unclear risk of attrition	1	147	Odds Ratio (M‐H, Fixed, 95% CI)	2.04 [0.93, 4.50]
2.6.2 Low risk of attrition	9	1645	Odds Ratio (M‐H, Fixed, 95% CI)	1.75 [1.39, 2.19]
2.6.3 High risk of attrition	1	268	Odds Ratio (M‐H, Fixed, 95% CI)	1.46 [0.85, 2.50]
2.7 Ovarian hyperstimulation syndrome rate Show forest plot	10	1848	Risk Difference (M‐H, Fixed, 95% CI)	‐0.00 [‐0.01, 0.01]

2.7.1 AIs versus clomiphene citrate	8	1572	Risk Difference (M‐H, Fixed, 95% CI)	‐0.00 [‐0.01, 0.00]
2.7.2 Aromatase inhibitor + hMG versus clomiphene + hMG	2	276	Risk Difference (M‐H, Fixed, 95% CI)	0.00 [‐0.04, 0.04]
2.8 Ovarian hyperstimulation syndrome rate by BMI Show forest plot	9		Risk Difference (M‐H, Fixed, 95% CI)	Subtotals only

2.8.1 BMI > 25	4	1163	Risk Difference (M‐H, Fixed, 95% CI)	‐0.01 [‐0.01, 0.00]
2.8.2 BMI < 25	5	605	Risk Difference (M‐H, Fixed, 95% CI)	0.00 [‐0.02, 0.02]
2.9 Clinical pregnancy rate Show forest plot	23	3321	Odds Ratio (M‐H, Fixed, 95% CI)	1.69 [1.45, 1.98]

2.9.1 Aromatase inhibitor versus clomiphene citrate	17	2516	Odds Ratio (M‐H, Fixed, 95% CI)	1.70 [1.42, 2.03]
2.9.2 Aromatase inhibitor + metformin versus clomiphene + metformin	3	294	Odds Ratio (M‐H, Fixed, 95% CI)	1.86 [1.05, 3.29]
2.9.3 Aromatase inhibitor + hMG versus clomiphene + hMG	2	276	Odds Ratio (M‐H, Fixed, 95% CI)	1.37 [0.82, 2.27]
2.9.4 AIs versus tamoxifen	2	135	Odds Ratio (M‐H, Fixed, 95% CI)	1.58 [0.64, 3.90]
2.9.5 AIs versus clomiphene + estradiol valerate	1	100	Odds Ratio (M‐H, Fixed, 95% CI)	2.47 [0.94, 6.46]
2.10 Impact of allocation bias for clinical pregnancy rate Show forest plot	21		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

2.10.1 Unclear risk of allocation	17	1931	Odds Ratio (M‐H, Fixed, 95% CI)	1.74 [1.41, 2.14]
2.10.2 Low risk of allocation	4	580	Odds Ratio (M‐H, Fixed, 95% CI)	1.56 [1.10, 2.21]
2.11 Miscarriage rate per woman Show forest plot	15	2422	Odds Ratio (M‐H, Fixed, 95% CI)	1.37 [1.01, 1.87]

2.11.1 AIs versus clomiphene citrate	10	1752	Odds Ratio (M‐H, Fixed, 95% CI)	1.40 [0.98, 1.99]
2.11.2 Aromatase inhibitor + metformin versus clomiphene + metformin	3	294	Odds Ratio (M‐H, Fixed, 95% CI)	1.21 [0.52, 2.82]
2.11.3 Aromatase inhibitor + hMG versus clomiphene + hMG	2	276	Odds Ratio (M‐H, Fixed, 95% CI)	0.84 [0.31, 2.27]
2.11.4 AIs versus clomiphene + estradiol valerate	1	100	Odds Ratio (M‐H, Fixed, 95% CI)	12.21 [0.66, 226.97]
2.12 Miscarriage rate per pregnancy Show forest plot	15	736	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.66, 1.32]

2.12.1 AIs versus clomiphene citrate	10	529	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.63, 1.42]
2.12.2 Aromatase inhibitor + metformin versus clomiphene + metformin	3	79	Odds Ratio (M‐H, Fixed, 95% CI)	0.80 [0.32, 2.02]
2.12.3 Aromatase inhibitor + hMG versus clomiphene + hMG	2	104	Odds Ratio (M‐H, Fixed, 95% CI)	0.67 [0.23, 1.96]
2.12.4 AIs versus clomiphene + estradiol valerate	1	24	Odds Ratio (M‐H, Fixed, 95% CI)	8.13 [0.39, 167.90]
2.13 Multiple pregnancy rate Show forest plot	14	2247	Odds Ratio (M‐H, Fixed, 95% CI)	0.74 [0.42, 1.32]

2.13.1 Aromatase inhibitor versus clomiphene citrate	12	1971	Odds Ratio (M‐H, Fixed, 95% CI)	0.69 [0.35, 1.34]
2.13.2 Aromatase inhibitor + hMG versus clomiphene + hMG	2	276	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.29, 3.05]

Comparison 2. Letrozole compared to SERM with or without adjuncts, followed by timed intercourse

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Comparison 3. Letrozole compared to SERMs with our without adjuncts, followed by IUI

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
3.1 Ovarian hyperstimulation syndrome rate Show forest plot	2	1494	Risk Difference (M‐H, Fixed, 95% CI)	‐0.00 [‐0.01, 0.00]

3.1.1 AI versus clomiphene	1	107	Risk Difference (M‐H, Fixed, 95% CI)	‐0.02 [‐0.07, 0.03]
3.1.2 AI versus clomiphene + rFSH and rFSH only	1	1387	Risk Difference (M‐H, Fixed, 95% CI)	‐0.00 [‐0.01, 0.00]
3.2 Clinical pregnancy rate Show forest plot	3	1597	Odds Ratio (M‐H, Fixed, 95% CI)	1.71 [1.30, 2.25]

3.2.1 AI versus clomiphene	2	210	Odds Ratio (M‐H, Fixed, 95% CI)	2.09 [0.97, 4.53]
3.2.2 AI versus clomiphene + rFSH and rFSH only	1	1387	Odds Ratio (M‐H, Fixed, 95% CI)	1.66 [1.23, 2.22]
3.3 Miscarriage rate per woman Show forest plot	2	1490	Odds Ratio (M‐H, Fixed, 95% CI)	1.22 [0.62, 2.40]

3.3.1 AI versus clomiphene	1	103	Odds Ratio (M‐H, Fixed, 95% CI)	0.32 [0.01, 8.06]
3.3.2 AI versus clomiphene + rFSH and rFSH only	1	1387	Odds Ratio (M‐H, Fixed, 95% CI)	1.32 [0.66, 2.65]
3.4 Miscarriage rate per pregnancy Show forest plot	2	260	Odds Ratio (M‐H, Fixed, 95% CI)	0.76 [0.37, 1.57]

3.4.1 AI versus clomiphene	1	15	Odds Ratio (M‐H, Fixed, 95% CI)	0.10 [0.00, 3.09]
3.4.2 AI versus clomiphene + rFSH and rFSH only	1	245	Odds Ratio (M‐H, Fixed, 95% CI)	0.85 [0.40, 1.79]
3.5 Multiple pregnancy rate Show forest plot	3	1597	Odds Ratio (M‐H, Fixed, 95% CI)	1.03 [0.49, 2.13]

3.5.1 AI versus clomiphene	2	210	Odds Ratio (M‐H, Fixed, 95% CI)	3.48 [0.14, 87.49]
3.5.2 AI versus clomiphene + rFSH and rFSH only	1	1387	Odds Ratio (M‐H, Fixed, 95% CI)	0.94 [0.44, 2.03]

Comparison 3. Letrozole compared to SERMs with our without adjuncts, followed by IUI

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Comparison 4. Letrozole compared to laparoscopic ovarian drilling

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
4.1 Live birth rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

4.2 Clinical pregnancy rate Show forest plot	3	367	Odds Ratio (M‐H, Fixed, 95% CI)	1.47 [0.95, 2.28]

4.2.1 AI versus LOD	2	221	Odds Ratio (M‐H, Fixed, 95% CI)	1.69 [0.96, 2.97]
4.2.2 AI + metformin versus LOD	1	146	Odds Ratio (M‐H, Fixed, 95% CI)	1.20 [0.60, 2.39]
4.3 Miscarriage rate per woman Show forest plot	3	367	Odds Ratio (M‐H, Fixed, 95% CI)	0.87 [0.31, 2.44]

4.3.1 AI versus LOD	2	221	Odds Ratio (M‐H, Fixed, 95% CI)	0.58 [0.14, 2.50]
4.3.2 AI + metformin versus LOD	1	146	Odds Ratio (M‐H, Fixed, 95% CI)	1.35 [0.29, 6.27]
4.4 Miscarriage rate per pregnancy Show forest plot	3	122	Odds Ratio (M‐H, Fixed, 95% CI)	0.65 [0.22, 1.92]

4.4.1 AI versus LOD	2	73	Odds Ratio (M‐H, Fixed, 95% CI)	0.38 [0.08, 1.72]
4.4.2 AI + metformin versus LOD	1	49	Odds Ratio (M‐H, Fixed, 95% CI)	1.21 [0.24, 6.09]
4.5 Multiple pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

Comparison 4. Letrozole compared to laparoscopic ovarian drilling

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Comparison 5. Letrozole compared to FSH

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
5.1 Live birth Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

5.2 Ovarian hyperstimulation syndrome rate Show forest plot	2	236	Risk Difference (M‐H, Fixed, 95% CI)	‐0.03 [‐0.08, 0.01]

5.3 Clinical pregnancy rate Show forest plot	2	236	Odds Ratio (M‐H, Fixed, 95% CI)	0.81 [0.46, 1.43]

5.4 Miscarriage rate per woman Show forest plot	2	236	Odds Ratio (M‐H, Fixed, 95% CI)	0.61 [0.19, 1.92]

5.5 Miscarriage rate per pregnancy Show forest plot	2		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

5.6 Multiple pregnancy rate Show forest plot	2	236	Odds Ratio (M‐H, Fixed, 95% CI)	0.22 [0.04, 1.32]

Comparison 5. Letrozole compared to FSH

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Comparison 6. Letrozole compared to anastrozole

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
6.1 Clinical pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

6.2 Multiple pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

Comparison 6. Letrozole compared to anastrozole

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Comparison 7. Letrozole compared to berberine, followed by timed intercourse

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
7.1 Live birth rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

7.2 Clinical pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

7.3 Miscarriage rate per woman Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

7.4 Miscarriage rate per pregnancy Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

7.5 Multiple pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Subtotals only

Comparison 7. Letrozole compared to berberine, followed by timed intercourse

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Comparison 8. Different administration protocols of letrozole

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
8.1 Clinical pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

8.1.1 Letrozole day 3‐7 administration versus day 5‐9 administration	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

Comparison 8. Different administration protocols of letrozole

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Comparison 9. Dosage studies of letrozole

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
9.1 Ovarian hyperstimulation syndrome rate Show forest plot	1		Risk Difference (M‐H, Fixed, 95% CI)	Totals not selected

9.1.1 5 mg versus 7.5 mg letrozole	1		Risk Difference (M‐H, Fixed, 95% CI)	Totals not selected
9.2 Clinical pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

9.2.1 5 mg versus 7.5 mg letrozole	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected
9.3 Miscarriage rate per woman Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

9.3.1 5 mg versus 7.5 mg letrozole	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected
9.4 Miscarriage rate per pregnancy Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

9.4.1 5 mg versus 7.5 mg letrozole	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected
9.5 Multiple pregnancy rate Show forest plot	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

9.5.1 5 mg versus 7.5 mg letrozole	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected

Comparison 9. Dosage studies of letrozole

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