1. Letrozole, an aromatase inhibitor, is more effective than clomiphene for treatment of infertility in women with PCOS.
2. There was no significant difference in number of congenital abnormalities.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Polycystic ovarian syndrome (PCOS) is a common cause of infertility in women. It is a condition characterized by hormonal imbalance, leading to irregular and infrequent ovulation. The goal of fertility treatments for women with PCOS is to induce ovulation. Clomiphene is currently the treatment of choice. It antagonizes estrogen receptors and blocks the negative feedback of estrogen on the hypothalamus, thereby increasing gonadotropin levels and enhancing ovarian stimulation.
This study finds that letrozole, an aromatase inhibitor, is more effective than clomiphene for the treatment of infertility in women with PCOS. Live births occurred in 27.5% of women on letrozole vs. 19.1% of women on clomiphene.
Like clomiphene, letrozole enhances ovarian stimulation by reducing negative feedback on the hypothalamus. However, letrozole achieves this by inhibiting estrogen synthesis rather than antagonizing estrogen receptors directly. Although not statistically significant, it is interesting to note that letrozole appeared to be more effective (in terms of cumulative live births) in women with a BMI over 30.3 as adipose tissue is known to express aromatase.
In-Depth [randomized controlled trial]: The study enrolled 750 infertile women with PCOS from 18 to 40 years of age. PCOS was diagnosed based on the presence of ovulatory dysfunction with hyperandrogenism, polycystic ovaries, or both. Women were randomized to either 50mg of clomiphene daily or 2.5mg of letrozole daily for 5 days. In the case of a poor ovulatory response, the doses of each medication were increased for each subsequent menstrual cycle for up to 5 cycles or until adequate ovulatory response.
The primary outcome was live birth during treatment period. Letrozole performed better than clomiphene (27.5% vs. 19.1%, p=0.007). There were 5 major congenital anomalies, four with letrozole and one with clomiphene (p=0.65). For comparison, the rate of congenital abnormalities in a population of healthy, fertile women was 5.8% in one study.
The authors did not find an interaction between BMI and treatment in terms of time from randomization to live birth. Their data also showed that letrozole may be more effective in terms of cumulative live births in women with BMI >30.3 (p=0.03).
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