Oral agents for ovulation induction--clomiphene citrate versus aromatase inhibitors

The purpose of this review is to compare clomiphene citrate (CC) with aromatase inhibitors (AI) as the first-line therapy for WHO Group II (eu-oestrogenic) infertility. For the past 45 years CC has been the first-line therapy, as it is a simple, cheap treatment, almost devoid of side effects, and yields ovulation in 73%, pregnancy in 36% and a singleton live birth rate of 25%. The gap between ovulation and pregnancy rates has mainly been attributed to its anti-oestrogen effects on endometrium. AI block oestrogen production, not oestrogen receptors, and would therefore be expected to produce superior conception rates and less multiple pregnancies. AI have yet to undergo further large, robust clinical trials in order to fulfill this promise as a feasible alternative to CC in this role, but some preliminary trials have shown at least equality and some superiority.