**2.2. Letrozole**

Letrozole is an aromatase inhibitor that is now recommended as a first line ovulation induction agent [6]. It is associated with higher rates of mono-ovulation than clomiphene and thus lower rates of multiple pregnancy, at around 3.5% [9], but with overall similar if not higher live birth rates [10]. It has a shorter half-life than clomiphene and, unlike clomiphene, during treatment endogenous FSH is suppressed by rising oestrogen levels thus reducing the risk of multiple follicles developing. Due to the benefit of increased live birth rates and a reduction in the rates of multiple pregnancy letrozole should be the oral agent for first line use in anovulatory women undergoing ovulation induction. However, letrozole must be used under informed consent as ovulation induction is not an approved indication for the drug.
