Endogenous progesterone levels could predict reproductive outcome in frozen embryo replacement cycles supplemented with synthetic progestogens: A retrospective cohort study

PURPOSE: A retrospective, cohort study was conducted between 2009 and 2017 in a private infertility center to determine the predictive value of endogenous estrogen (E2) and progesterone (P4) levels in hormone‐replacement frozen embryo replacement (FER) treatment cycles. METHODS: A total of 120 consecutive, infertile patients who became pregnant after FER cycles were analyzed (age: 37.4 ± 4.4 years). Electively vitrified blastocysts were created during natural cycle IVF or mild ovarian stimulation treatments and subsequently transferred through delayed vitrified‐thawed blastocyst transfer cycles supplemented with estrogens and a combination of synthetic progestogens. Serum E2 and progesterone P4 levels were intensively monitored every five days (from the day after embryo transfer until 9w1d of pregnancy) and compared among patients with a subsequent live birth (n = 76) or first‐trimester pregnancy loss (n = 44). RESULTS: Endogenous placental activity started as early as 5‐6th pregnancy week differing significantly according to pregnancy outcome. For P4, the exponential rise from 6w2d onwards allowed distinguishing between failing and successful conceptions. For P4, lower quartiles of the live birth group did not intersect with upper quartiles of the miscarriage group. CONCLUSIONS: Innovative FER protocols incorporating synthetic progestogens allow the correct measurement of endogenous placental activity and could help to monitor early first‐trimester ART pregnancies.