Serum progesterone and vaginal gel dose in artificial-cycle frozen embryo transfer: association with pregnancy outcome

Purpose: To evaluate the clinical relevance of serum progesterone levels on the day of frozen embryo transfer (FET) and the dose of vaginal progesterone gel (Crinone) used for early luteal phase support (LPS) in artificial-cycle frozen embryo transfer (AC-FET). Methods: This single-center retrospective study analyzed 342 AC-FET cycles in patients aged 18-45 at Changhua Christian Hospital, Taiwan (April 2018-December 2022). Women aged 18-45 years undergoing AC-FET were included; cycles with >3 prior failed FETs, major comorbidities, donor oocytes, or missing outcome data were excluded. Pregnancy outcomes were assessed per cycle. Crinone (90 mg or 180 mg daily) was administered for 5 days after endometrial thickness ≥7 mm and progesterone