A Cochrane review «Aromatase inhibitors (letrozole) for ovulation induction in infertile women with polycystic ovary syndrome»1 «»? included 41 studies with a total of 6522 subjects. Polycystic ovary syndrome (PCOS) is the most common cause of oligomenorrhoea and amenorrhoea. Live birth rates were higher with letrozole (with or without adjuncts) compared to clomiphene citrate (a selective oestrogen receptor modulator, SERM) with our without adjuncts followed by timed intercourse (table «Letrozole compared to clomifen (SERM) for infertile women with PCOS»1); number needed to treat (NNT) for an additional beneficial outcome 10.
| Outcome | Relative effect (95% CI) | Risk with control - SERM | Risk with intervention - letrozole (95% CI) | No of participants (studies) Certainty of evidence |
|---|---|---|---|---|
| Live birth rate | OR 1.72 (1.40 to 2.11) | 204 per 1000 | 307 per 1000 (265 to 352) | 2060 (11) High |
| Ovarian hyperstimulation syndrome rate | RD -0.00 (−0.01 to 0.01) | 7 per 1000 | 5 per 1000 (5 to 5) | 1848 (10) High |
| Miscarriage rate by pregnancies | OR 0.94 (0.66 to 1.32) | 252 per 1000 | 240 per 1000 (182 to 307) | 736 (15) High |
| Multiple pregnancy rate | OR 0.74 (0.42 to 1.32) | 22 per 1000 | 16 per 1000 (9 to 28) | 2247 (14) High |
A systematic review and meta-analysis «Liu Z, Geng Y, Huang Y, et al. Letrozole Compared With Clomiphene Citrate for Polycystic Ovarian Syndrome: A Systematic Review and Meta-analysis. Obstet Gynecol 2023;141(3):523-534. »2 included 29 RCTs with 3952 women and 7633 ovulation induction cycles. Pooled analysis indicated that letrozole treatment prevailed against clomiphene citrate in ovulation rate (RR 1.14, 95% CI 1.06 to 1.21; 22 trials, P <.001), clinical pregnancy rate (RR 1.48, 95% CI 1.34 to 1.63; 28 trials, P <.001), and live-birth rate (RR 1.49, 95% CI 1.27 to 1.74; 8 trials, P <.001).