The Association Between Serum E2 and P on the Day of FET and the Pregnancy Outcome

Study design a retrospective cohort study for 402 FET cycles which will be conducted in Al- Baraka Fertility Hospital, Manama, Bahrain, between April 2018 and May 2019. The trial registration number for the study is (NCT04114500), and it was approved by our ethical committee Study population

• Inclusion criteria were women who underwent FET, were age below 40 yrs., body mass index (BMI) below 30 kg/m2, patients who underwent FET treatment using the endometrial preparation was initiated with oral estradiol valerate, the endometrial thickness was no less than 8 mm on the day when P was administrated; with normal endometrial ultrasound imaging and euploid pre-genetically tested embryos;
• Exclusion criteria were chromosomal and genetic disorders, age> 40 years, BMI > 35 , abnormal ultrasonogram of uterine cavity (acquired or congenital) and abnormal embryos not suitable for transfer.

Study protocol Endometrial preparation in frozen embryo transfer (FET) briefly, patients received treatment with 2 mg/8h E2 (Estrofem, Novo Nordisk) for 12-14 days, Endometrial thickness was evaluated with transvaginal sonography. When endometrial thickness reached 8 mm or greater and was trilaminar in appearance, patients were initiated on both vaginal micronized P (Crinone gel, Merck) and oral P (Duphastone, Abott) treatment at 200 mg/8h. P4 was given as supplementation because normal ovarian steroid production and the ovarian follicular-to-luteal transition were suppressed with estradiol. A depot GnRH agonist was administered in the midluteal phase of the preceding cycle at clinician's discretion. On the early morning of day 5 of P treatment, the same day of FET, a blood sample was obtained and immediately analyzed. Hormone determinations of E2 and P were performed. Then, embryo transfer of the pre-genetically tested euploid embryos was performed under ultrasound guidance. 12 days later pregnancy test was assessed, 4 weeks after FET date ultrasound will be scheduled to check the viability and clinical pregnancy.