Research Question: What should be the optimal route of luteal support in programmed frozen embryo transfer (FET) cycles?
Design: This was a randomized, parallel, phase IV pilot trial with three groups of women undergoing FET along with hormone replacement therapy for endometrial preparation at a tertiary private IVF centre (NCT03948022). Women with at least one autologous cryopreserved blastocyst were included. After preparing the endometrium with oestradiol, 151 women were randomly assigned to one of the following three progesterone arms before embryo transfer: oral (10 mg) dydrogesterone (DYD), total daily dose 40 mg (n = 52); 8% (90 mg) progesterone vaginal gel (VAG), total daily dose 180 mg (n = 55); or intramuscular progesterone (IMP) 50 mg/ml in oil, total daily dose 100 mg (n = 44).