Does serum progesterone level impact the ongoing pregnancy rate in frozen embryo transfer under artificial preparation with vaginal progesterone? Study protocol for a randomized controlled trial.

BACKGROUND: In previous retrospective studies, low serum progesterone level on the embryo transfer day is associated with lower clinical pregnancy and ongoing pregnancy rates. Whether adding progesterone in low serum progesterone patients can rescue the outcome, there is no sufficient evidence from randomized controlled studies. METHODS: This trial is a clinical randomized controlled study (high serum progesterone vs low serum progesterone 1:1, 1:1 randomization ratio of intervention vs the control group with low serum progesterone). The eligible hormone replacement therapy-frozen embryo transfer (HRT-FET) cycles, will be recruited and randomly assigned to two parallel groups when serum progesterone is < 7.24µg/l on the day of embryo transfer for D3. The intervention group will be extrally given intramuscular progesterone 40 mg per day from D3 to 8 weeks of gestation if clinical pregnancy. The primary outcome is the ongoing pregnancy (beyond 12 weeks of gestation) rate. DISCUSSION: The findings of this study will provide strong evidence for whether the progesterone addition from the D3 in low serum progesterone patients can improve the outcome in the HRT-FET cycle. TRIAL REGISTRATION: ClinicalTrials.gov NCT04248309 . Registered on January 28, 2020.