Frozen embryo transfers (FET) now represent the majority of all embryo transfer cycles, and upwards of 60% live births in United States are now attributable to frozen embryo transfers (1). Exogenous progesterone for endometrial decidualization and luteal phase support is thought to be critical to both optimizing endometrial receptivity for implantation as well as sustaining early pregnancy prior to reliable secretory activity of the early placenta.
The purpose of this study is to:
1. Determine the prevalence of low serum progesterone levels (less than 10 ng/ml) among patients undergoing a programmed embryo transfer cycle on the day of frozen embryo transfer.
2. Determine if serum progesterone \< 10 ng/ml on the day of frozen embryo transfer is associated with poorer FET outcomes: ongoing pregnancy (primary outcome), live birth, biochemical pregnancy, and clinical pregnancy.