OBESITY IS ASSOCIATED WITH REDUCED PEAK SERUM ESTRADIOL CONCENTRATION IN PROGRAMMED HORMONE REPLACEMENT FROZEN EMBRYO TRANSFER CYCLES

Abstract

In addition to the assessment of endometrial lining thickness, serum estradiol concentration is often measured during programmed hormone replacement endometrial preparation cycles prior to frozen embryo transfer (FET) as a measure of adequate response. We investigated whether peak estradiol levels vary in overweight or obese women compared to normal and underweight women. A retrospective cohort study of patients who underwent a programmed hormone replacement endometrial preparation protocol prior to FET at Shady Grove Fertility centers was performed from January 1, 2017 to July 31, 2020. Patients were stratified by BMI according to the WHO BMI Classification system. Peak estradiol level was measured on the day the patient passed their endometrial lining check, which was defined as an endometrial thickness ≥8 mm on ultrasound. Exclusion criteria were natural cycle FET, uterine factor infertility, or initial endometrial preparation protocol that included Letrozole, injectable gonadotropin (Gonal-F), or a Phosphodiesterase inhibitor. Data were compared by students t-test and chi square as appropriate. 1009 cycles met inclusion criteria. Cycles were categorized as normal weight and underweight (BMI <24.9 kg/m2, n=475), overweight (BMI ≥ 25- 29.9 kg/m2, n=303), or obese (BMI ≥ 30 kg/m2, n=231). There was a statistically significant difference in peak estradiol level following estradiol treatment in preparation for FET based on BMI (normal and underweight 660.7 pg/ml, overweight 549.75 pg/ml, and obese 485.41 pg/ml, p=0.004). Despite the decrease in serum estradiol concentration with increasing BMI, the mean endometrial thickness prior to embryo transfer was not significantly different between the 3 respective groups (9.71 mm, 10.01 mm and 9.87 mm, p=0.288). The route of estradiol administration was not significantly different based on BMI, and the majority of patients in all BMI groups were on oral estradiol (71.8%, 68% and 74%). Additionally, the differences in estradiol level did not result in a difference in cycle outcome. The percentage of cycles resulting in clinical intrauterine gestations were 64.4%, 63.7% and 60.2% respectively. When adjusting for BMI, there remained no difference in clinical intrauterine gestations based on maximum E2 level (p=0.26). Increasing BMI was associated with a decreased peak estradiol level in FET cycles that utilized programmed hormone replacement endometrial preparation protocols, however this did not impact endometrial thickness or cycle outcome.