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

ObjectiveTo 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 DesignRetrospective analysis.SettingA 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.