Comparison of embryo developmental competence derived from letrozole and clomiphene citrate for ovarian stimulation in elderly infertile women

Abstract

There are infertile women, or poor responders, from whom oocytes cannot be retrieved because of a low response to hormonal ovarian stimulation. Most of these patients are over 40 years old. Clomiphene citrate (CC) treatment or natural cycle may be prescribed for these women during assisted reproductive technology (ART). Recently aromatase inhibitors (AIs) have been used for ovarian stimulation instead of CC or natural cycle. Letrozole (LZ) is one of the most popular AIs, but there are few comparative studies of the LZ and CC cycles. In particular, there are few analyses of developmental competence up to blastocyst stage and blastocyst transfer. The aim of this study was to compare the CC cycle to the LZ cycle for embryo developmental ability in infertile patients over 40 years old. We screened 2310 IVF cycles between 2009 and 2012 at our clinic. All patients were over 40 years old. The patients were supplemented with either LZ (n=1137) or CC (n=1173). Mature oocytes (LZ, n=658; CC, n=996) were used for IVF on oocyte retrieval (Day 0). At Day 1, embryos were cultured and vitrified when they progressed to the expanded blastocyst stage. Vitrificated blastocysts were warmed and transferred to patients. We compared outcomes of CC cycle and LZ cycle treated patients. In the LZ cycle, cancellation rates were significantly lower than those of the CC cycle (5.4% vs. 10.6%). The rates of cycle retrieved MII oocytes were not significantly different between the two groups. The blastocyst cryopreservation rate in the LZ cycle was significantly higher than that of the CC cycle (34.7% vs. 28.8%). There was no significant difference in the pregnancy rates between the two groups (CC, 35.1%; LZ, 30.7%). LZ treatment improves IVF outcomes in elderly patients because of lower cancelation rates and higher blastocyst cryopreservation rates. LZ may be the regimen of first choice to ovarian stimulation for patients over 40 years old.