Can letrozole-stimulated ovulation improve embryo transfer outcomes for women with PCOS?

This study compared two types of frozen embryo transfer (FET) for women with polycystic ovarian syndrome (PCOS). It found that stimulating ovulation with letrozole (Femara) led to fewer pregnancy complications than using an artificial cycle.

FET is an infertility treatment in which a frozen embryo is transferred into the uterus. It is now common to freeze many or all embryos following in vitro fertilization (IVF). Freezing allows fewer embryos to be transferred at a time.

FET’s success depends on the lining of the uterus being receptive to an embryo. The uterine lining changes throughout the menstrual cycle. FET can be timed for after ovulation, when the uterus is receptive. For women who do not ovulate regularly or at all, such as those with PCOS, there are two options. Ovarian stimulation FET (ov-FET) uses medications to cause ovulation. Alternately, a woman can take the hormones estrogens and progesterone to create an artificial cycle (AC). 

AC-FET has been shown to have higher rates of pregnancy complications related to high blood pressure. This includes pre-eclampsia, a condition in which the placenta develops abnormally. Pre-eclampsia can impact the woman’s liver and kidneys and can cause low birth weight and stillbirth.

It is not clear whether stimulating ovulation leads to better FET outcomes than AC for women with PCOS.

This study used records from 2,427 women with PCOS who became pregnant following FET. 1,168 women used an artificial cycle to prepare for the FET. The other patients used letrozole alone or with gonadotropins (Gonal-F) to stimulate ovulation.

Single pregnancies from ovulation stimulation (ov-FET) had 37% lower odds of blood pressure complications than those from AC-FET. Also, the rate of Cesarean section was significantly lower for single pregnancies when using ov-FET.

Similar numbers of women developed diabetes during pregnancy in the two groups. Also, babies conceived using the two FET methods had similar birth weights.

This study found that ov-FET led to fewer blood pressure pregnancy complications than AC-FET for patients with PCOS.

Using ov-FET requires frequent monitoring to determine when ovulation has occurred. It may be more difficult for patients who live far from their fertility clinic.