The quality of evidence is downgraded by study limitations (unclear allocation concealment in half of the studies and possible selective reporting).
A Cochrane review included 42 studies with a total of 7935 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 (with our without adjuncts) followed by timed intercourse (table ); number needed to treat (NNT) for an additional beneficial outcome 10. Ovarian hyperstimulation syndrome (OHSS) rates and miscarriage rates were similar with letrozole or clomiphene citrate. Live birth rates were similar with letrozole or laparoscopic ovarian drilling, but evidence for a difference in OHSS rates or miscarriage rates was insufficient (table ). There is insufficient evidence for comparison with letrozole vs placebo or letrozole vs selective oestrogen receptor modulators (SERMS).
| Outcome | Relative effect (95% CI) | Risk with control- clomifen | Risk with intervention - letrozole (95% CI) | No of participants (studies) Certainty of evidence |
|---|---|---|---|---|
| Live birth rate | OR 1.68 (1.42 to 1.99) | 214 per 1000 | 314 per 1000 (279 to 352) | 2954 (13) Moderate |
| OHSS | Risk difference (RD) 0.00 (−0.01 to 0.00) | 5 per 1000 | 5 per 1000 (5 to 5) | 2536 (12) High |
| Clinical pregnancy rate | OR 1.56 (1.37 to 1.78) | 264 per 1000 | 359 per 1000 (330 to 390) | 4629 (25) Moderate |
| Miscarriage rate by pregnancies | OR 0.94 (0.70 to 1.26) | 201 per 1000 | 191 per 1000 (150 to 240) | 1210 (18) High |
| Multiple pregnancy rate | OR 0.69 (0.41 to 1.16) | 17 per 1000 | 13 per 1000 (7 to 21) | 3579 (17) High |
| Outcome | Relative effect (95% CI) | Risk with control - ovarian drilling | Risk with intervention - letrozole (95% CI) | No of participants (studies) Certainty of evidence |
|---|---|---|---|---|
| Live birth rate | OR 1.38 (0.95 to 2.02) | 236 per 1000 | 299 per 1000 (227 to 385) | 548 (3) Low |
| Ovarian hyperstimulation syndrome rate | RD 0.00 (−0.01 to 0.01) | 0 per 1000 | 0 per 1000 (0 to 0) | 260 (1) Low |
| Miscarriage rate by pregnancies | OR 0.66 (0.30 to 1.43) | 145 per 1000 | 101 per 1000 (49 to 196) | 240 (5) Moderate |
| Multiple pregnancy rate | OR 3.00 (0.12 to 74.90) | 0 per 1000 | 0 per 1000 (0 to 0) | 548 (3) Low |
Date of latest search:2018-06-14