P-445 High serum estradiol on the day of frozen blastocyst transfer is associated with higher early miscarriage rates in hormonal replacement therapy cycles using transdermal estrogens
Authors: Maignien C , Jobin T , Bourdon M , Blanchet V , Laguillier-Morizot C , Patrat C , Chapron C , Santulli P 
Published: July 2024

Abstract

Study question
Do serum estradiol(E2) levels on the day of frozen blastocyst transfer(FBT) affect the live birth rate (LBR) in hormonal replacement therapy(HRT) cycles using transdermal estrogens?

Summary answer
E2 levels ≥ 313 pg/mL on the day of FBT are associated with increased early miscarriage rates, but no significant impact on LBR.

What is known already
E2 plays a crucial role in endometrial receptivity during the periconceptional period and a massive role in placentation. However, the impact of serum E2 levels measured around the time of a FBT in HRT cycles outcomes remains controversial, with some studies showing a detrimental impact of high levels, and others underlining no difference. To this date, there is no study focusing on HRT cycles with transdermal estrogens only, though it is the safest way of estrogen administration regarding thrombo-embolic complications.

Study design, size, duration
Observational cohort study with 2364 patients undergoing HRT-FBT cycles at a university hospital, between January 2019 and December 2022. Women were only included once during the study period.

Participants/materials, setting, methods
Patients undergoing single autologous FBT under HRT using transdermal estrogens and vaginal micronized progesterone. The serum E2 level was measured in the morning of the FBT, in a single laboratory. The primary outcome was the LBR, secondary outcomes included clinical pregnancy rates, early miscarriage rates(EMR), and obstetrical outcomes. Patients were divided into three groups based on the 25th and the 75th percentiles of E2 levels and compared using univariate and multivariate logistic regression models.

Main results and the role of chance
A total of 2364 patients were divided into 3 groups: group A &lt; 122 pg/mL (n = 590), group B 122-312 pg/mL (n = 1184), and group C ≥ 313 pg/mL (n = 590). Mean serum E2 level on the day of FBT was 247.8 pg/mL ± 209.01 pg/ml. The LBR was 32.0% (756/2364), and the early miscarriage rate was 26.3% (280/1075) in the overall population. Multivariate logistic regression showed a negative impact of high E2 levels (≥ 313 pg/mL) on EMR: an increase in the EMR was noted between group C and referent group B (30.3% versus 24.6%, OR 1.5 95%CI (1.06-2.17)). However, no significant impact of E2 levels was noted regarding the LBR (group C vs group B, adjusted OR 0.9 95%CI (0.69-1.10)), the clinical pregnancy rates, or the obstetrical outcomes (birthweight and term of delivery

Limitations, reasons for caution
The main limitation of our study is linked to its observational design. Extrapolation of our results to other laboratories, or other routes and/or doses of administering estrogens also needs to be validated.

Wider implications of the findings
Limiting high serum E2 levels on the day of FBT in HRT cycles may improve ART outcomes. Further studies are needed to evaluate if modifications of estrogen doses may improve pregnancy chances, in an approach to individualize the management of ART patients.

Trial registration number
not applicable