In some studies, early pregnancy loss (EPL) rate is higher with artificial cycle (AC) endometrial preparation for frozen-thawed embryo (FET) transfer than with other protocols, even though pregnancy rates are similar. An inadequate luteal phase support could explain these findings. The aim of this study was to compare, among the patients who had a pregnancy after FET with AC endometrial preparation, serum progesterone (PG) levels between those who experienced an EPL or an ongoing pregnancy.

A monocentric retrospective cohort study, conducted at a University affiliated fertility center, studied 130 FET cycles with AC endometrial preparation between June 2016 and July 2017. Serum PG rates were compared according to reproductive outcomes and to endometrial preparation protocol on day 10 or 12 after FET (PG0) according to the embryo stage, and every 48h in case of pregnancy (i.e. PG1; PG2).

Among patients who had a pregnancy after FET with AC (n=33), serum PG levels were higher in case of an ongoing pregnancy than EPL, only significantly at PG1 (PG0 12.4ng/mL [7.5−14.6] vs 8.2ng/mL [6.0−13.0], p= 0.320; PG1 15.0 ng/mL [14.0−15.9] vs 8.5ng/mL [5.9−13.8], p= 0.048).

We found that serum PG level was lower in women experiencing early pregnancy loss after FET with AC endometrial preparation, potentially reflecting a lack of appropriate luteal phase support with PG. A cycle AC test, monitoring serum PG levels after its steady state, could detect this lack of PG, allowing physicians to adapt PG supplementation.