Effect of preovulatory progesterone elevation and duration of progesterone elevation on the pregnancy rate of frozen-thawed embryo transfer in natural cycles.

Objective: To assess the incidence of P elevation (PE) in natural cycles and evaluate its effect on frozen-thawed embryo transfer cycles performed in natural cycles (FET-NC).

Study Design: Retrospective analysis.

Setting: A tertiary assisted reproductive unit.

Patient(s): Subfertile woman who did not conceive in their stimulated IVF cycle and underwent the first FET-NC cycle.

Intervention(s): Achieved serum samples were assayed for P concentrations from the day of LH surge up to 3 days before the surge. The cutoff level of PE was defined as 5 nmol/L.

Main Outcome Measure(s): Clinical and ongoing pregnancy rates.

Result(s): The incidence of PE in natural cycles was 173 of 610 (28.4%). There were no significant differences in both clinical and ongoing pregnancy rates (39.0% vs. 37.3% and 32.5% vs. 31.7%) between those with vs. without PE on the day of LH surge. If PE lasted for 2 days or more, there was a significant reduction in the clinical pregnancy rate (39.4% vs. 20.7%). Using multivariate logistic regression, women's age, PE for 2 days or more, and the number of top-quality embryos were the significant factors for clinical pregnancy rates in FET-NC.

Conclusion(s): The incidence of PE in FET-NC was similar to that in stimulated cycles. Progesterone elevation for 2 days or more before the LH surge impaired the clinical pregnancy rate of FET-NC, whereas PE on the day of LH surge only did not have such an adverse effect.