Serum Progesterone on the Day of Thawed Embryo Transfer and Pregnancy Rate After an Artificial Endometrial Preparation

Inclusion Criteria: * women between age 18-38 undergoing FET in AC * with body mass index (BMI) \< 35 kg/m2 * a triple layer endometrium \>6.5 mm after exogenous estrogen administration * 1-2 good quality day 3 or 5 FET. Exclusion Criteria: * women with recurrent pregnancy losses (e.g. 2 abortions beyond 12th week or 3 abortions before 12th week) * recurrent implantation failure (e.g. unsuccessful implantation of ≥4 good quality embryos) * severe male factor (sperm concentration \<5 million/ml), or presence of hydrosalpinx.