Comparison of endometrial preparation protocols (natural cycle versus hormone replacement cycle) for frozen embryo transfer (COMPETE): a study protocol for a randomised controlled trial

Introduction Natural cycle (NC) and hormone replacement treatment (HT) are frequently used endometrial preparation protocols prior to frozen-thawed embryo transfer in ovulatory women. It is not clear which protocol results in a higher live birth rate. It has been suggested that there is an increased risk in maternal and perinatal morbidity following HT protocol due to the lack of corpus luteum. The objective of this trial is to compare the clinical outcomes of NC and HT protocols in frozen embryo transfer.Methods and analysis COMPETE is an open-label, single-centre, randomised controlled trial targeting to recruit 888 women, with 444 women each in two arms (1:1 treatment ratio). Women undergoing in vitro fertilisation scheduled for a frozen embryo transfer and have a regular menstrual cycle are eligible. Exclusion criteria include ovulation disorders and intrauterine adhesions. The primary outcome is live birth resulting from the first frozen embryo transfer after randomisation. Secondary outcomes include biochemical pregnancy, clinical pregnancy, multiple pregnancy, ongoing pregnancy, miscarriage, endometrial thickness, cycle cancellation, gestational diabetes mellitus, hypertensive disorders of pregnancy, antepartum haemorrhage, preterm birth, birth weight, large for gestational age, congenital anomaly and perinatal mortality. The data analysis will be following the intention-to-treat principle.Ethics and dissemination This study has been approved by the Institutional Review Board of Northwest women’s and children’s hospital (2020008). Written informed consent will be obtained from each participant before randomisation. The results of the trial will be presented via publications.Trial registration number ChiCTR2000040640.