Outcomes with up to six months of treatment and timed intercourse	Probable outcome with clomiphene	Probable outcome with letrozole (95% CI)	NNT for outcome with letrozole (95% CI)	Number of participants (number of studies)	Quality of evidence
Pregnancy*	264 per 1,000	359 per 1,000 (330 to 390)	11 (8 to 15)	4,629 (25 RCTs)	Moderate
Live birth rate	214 per 1,000	314 per 1,000 (279 to 352)	10 (7 to 15)	2,954 (13 RCTs)	Moderate
Ovarian hyperstimulation syndrome	5 per 1,000	5 per 1,000 (5 to 6)	NA†	2,536 (12 RCTs)	High
Miscarriage rate	201 per 1,000	191 per 1,000 (150 to 240)	NA†	1,210 (18 RCTs)	High
Twin or other multiple pregnancy	17 per 1,000	13 per 1,000 (7 to 21)	NA†	3,579 (17 RCTs)	High