What is the best method to prepare the womb lining for frozen embryo transfer?

This study looked at how methods used to prepare the womb lining affect the success of frozen embryo transfers. This study found that mild ovary stimulation was associated with better pregnancy outcomes compared to an artificial cycle.

In vitro fertilization (IVF) is an infertility treatment where the eggs are collected, fertilized, and then implanted into a woman's womb. If multiple embryos (fertilized eggs) are produced, these may be frozen for use in future cycles of IVF. Using a frozen embryo in IVF means that it is transferred into the womb (embryo transfer). 

Before a frozen embryo transfer, hormones are used to help prepare the womb for the embryo. There are different ways to do this. In mild ovary stimulation (OS), hormones help the body produce progesterone, an essential hormone for pregnancy. In an artificial cycle (AC), estradiol (such as Yuvafem) and progesterone are used. It is not clear whether AC leads to a more successful embryo transfer compared to mild stimulation.

This study had 1021 patients. 664 patients received AC and 357 patients received OS. All patients had similar ages, body weights, and pregnancy histories. However, patients in the AC group were more likely to have endometriosis or polycystic ovarian syndrome (PCOS).

Overall, similar numbers of patients in both groups became pregnant (24.4%, OS vs. 20.8%, AC). However, significantly fewer patients who had OS had an early miscarriage compared to the AC group (24.1% vs 43.5%).

Significantly more patients who had OS were still pregnant 12 weeks later compared to the AC group (17.9% vs 11.0%). Significantly more patients who had OS also had a successful pregnancy (live birth) compared to the AC group (17.1% vs 9.8%). After adjusting for endometriosis, PCOS, smoking, and a history of miscarriages, outcomes were still significantly better for the OS group.

This study found that mild ovary stimulation was associated with better pregnancy outcomes compared to an artificial cycle. The authors suggest that mild OS could become the standard approach to prepare for an embryo transfer.

This study was retrospective (used patient records). Also, whether mild OS is effective for women with PCOS is unclear. More studies are needed to confirm these results.