Serum estradiol and progesterone levels at different time points in the menstrual cycle as predictors of outcome in frozen embryo transfer cycles

Objective: To investigate whether serum estradiol and progesterone levels at different time points in the menstrual cycle influence pregnancy outcomes in frozen embryo transfer cycles. Methods: This was a prospective cohort study of women aged <40 years undergoing frozen single blastocyst transfer. Endometrial preparation was achieved with 14 days of oral estradiol, followed by vaginal progesterone. Serum estradiol and progesterone levels were measured at four time points: T1, at the start of the menstrual cycle prior to hormone supplementation; T2, on the day of progesterone initiation; T3, on the day of embryo transfer; and T4, on the third day after embryo transfer. Results: In total, 205 women [mean age 32.4 (standard deviation 4.9) years] were included in this study. Serum estradiol levels at T1 and T2 were significantly higher in patients who achieved pregnancy compared with those who did not (median 20.5 vs 16.6 pg/ml, p = 0.005; 306.5 vs 257 pg/ml, p = 0.017, respectively). At T2, an estradiol threshold of 204.0 pg/ml had 84 % sensitivity and 37 % specificity for predicting clinical pregnancy [area under curve (AUC) 0.606, 95 % confidence interval (CI) 0.523-0.688]. The progesterone level at T3 had an optimal threshold of 14.97 ng/ml for predicting clinical pregnancy (AUC 0.610, 95 % CI 0.527-0.693). Conclusions: The findings suggest that in women undergoing frozen embryo transfer with hormone replacement, serum estradiol >204.0 pg/ml on the day of progesterone initiation and serum progesterone >14.97 ng/ml on the day of embryo transfer are associated with higher clinical pregnancy rates.