Progesterone Levels on the Day of Frozen-thawed Embryo Transfer in Artificial Cycles with Vaginal Progesterone Do not Predict Clinical Pregnancy: a Prospective Study

Some studies have reported that low serum progesterone (P) levels on the day of frozen-thawed embryo transfer (FET) are associated with lower pregnancy rates following artificial endometrial preparation (AEP) cycles. Other studies, however, have found no consistent association between serum P levels and pregnancy outcomes. This prospective cohort study included 235 patients who underwent FET following AEP cycles with estradiol valerate and vaginal micronized P. All patients received either blastocyst- or cleavage-stage embryos derived from their own oocytes, without preimplantation genetic testing for aneuploidies. Blood samples were collected on the day of FET to measure serum P concentrations. Serum P levels on the day of embryo transfer did not differ significantly between patients who achieved CP and those who did not (12.76 ± 4.1 ng/mL vs. 11.9 ± 5.6 ng/mL; p = 0.3318). The optimal serum P cutoff level associated with higher CP rates was 10.6 ng/mL, with a sensitivity of 72%, a specificity of 44%, and an AUC of 0.58, indicating poor predictive value. However, patients with serum P levels above this cutoff had a significantly higher CP rate than those with lower values (25.9% vs. 14.6%; p = 0.0372). In the multivariate logistic regression model, this difference was not statistically significant (OR = 2; 95% CI: 0.9–5). Routine monitoring of serum P levels on the day of embryo transfer in AEP cycles using vaginal micronized P is not justified, as serum P levels do not effectively predict CP outcomes in cycles using autologous oocytes.