MIcronized PROgesterone in Frozen Embryo Transfer Cycles

This randomized trial was designed as non-inferiority trial aiming to compare ongoing pregnancy rates following LPS with 600 mg/day vs 800 mg/day vaginal VMP. All patients will undergo an artificial cycle frozen embryo transfer (AC-FET) with transdermal estradiol 6mg/day Patients undergoing an artificial cycle FET will start estrogen priming with transdermal estradiol 6mg/day (Estrogel®) on cycle D1-D3. Following 10-12 days of estrogen priming, patients will be randomized to luteal phase support with a standard formulation (200mg tid, Utrogestan®) or a new formulation (400mg bid) VMP. All patients will undergo a serum P measurement on the day before embryo transfer (ET). Patients with P\<10 ng/ml will receive a supplement of oral micronized progesterone 300mg, while patients with P≥10ng/ml will maintain the previous luteal phase support (LPS) protocol