Can endocrine characteristics of early pregnancy following natural cycle cryopreserved embryo transfer predict live birth?

Research question: Can serial measurements of serum oestradiol, progesterone and β-human chorionic gonadotrophin (HCG) concentrations, starting from the day of the first positive pregnancy test, predict live birth after natural cycle frozen-thawed embryo transfer (NC-FET)? Design: This was a historical cohort study of women with a positive pregnancy test following NC-FET, between March 2009 and January 2020. Serum β-HCG, oestradiol and progesterone concentrations were measured on the day of the first pregnancy test and 48 and 96 h later. Pregnancies resulting in a live birth were compared with non-viable pregnancies. Results: Of 101 women with a positive pregnancy test included in the study, 78 had a live birth and 23 had a non-viable pregnancy. Serum β-HCG concentrations were comparable on the day of the first pregnancy test (P = 0.09) but became significantly higher in women with a live birth 48 and 96 h later (P = 0.018 and P = 0.003). Serum oestradiol concentrations were higher in women with a live birth at all three measurements (P = 0.02, P = 0.007 and P = 0.02). Serum progesterone concentrations were higher 48 h after the first pregnancy test in women with a live birth (P = 0.04). On multivariate analysis, after controlling for the women's ages and number of embryos transferred, serum concentrations above the 25th percentile for oestradiol (>488–526 pmol/L) and progesterone (>63–70 nmol/L) were independent predictors of live birth at all three measurements. Conclusions: Increased serum oestradiol and progesterone concentrations in early NC-FET pregnancies are associated with increased likelihood of live birth. Oestradiol and progesterone concentrations can be used in conjunction with β-HCG to predict pregnancy viability and assist in patient counselling.