P-528 Intra-individual variability of serum progesterone level on the day of frozen blastocyst transfers in hormonal replacement therapy cycles
Authors: Guihard C , Bourdon M , Maignien C , Patrat C , Guibourdenche J , Chapron C , Santulli P 
Published: June 2023

Abstract

Study question
Is there a significant intra-individual variability of serum progesterone level on the day of theHormone Replacement Therapy Frozen Embryo Transfer(HRT-FET) between two consecutive cycles?

Summary answer
No significant intra-individual variability of progesterone level measured the day of transfer was shown between two consecutive HRT-FET cycles.

What is known already
In frozen embryo transfer under HRT, a minimum P level around the day of embryo transfers necessary to optimize reproductive outcomes. Indeed, in a previous study, we have found that women with a serum P level ≤9.8ng/ml on the day of the single autologous blastocyst transfer had lower live birth rate. Moreover, some clinical factors have been described as influencing the P level on the day of the embryo transfer (i.e weight, gravidity, Ethnic origin,tobacco consumption…). Variations between patients raise the question of intra-individual variation in P measurement, in addition to the existence of inter-individual variation.

Study design, size, duration
We conducted an observational cohort study at the university-based reproductive medicine centre of our institution that focusing on women who underwent at least two consecutive single autologous HRT-FET of blastocyst, between January 2019 and March 2020.

Participants/materials, setting, methods
Patients undergoing two consecutive single autologous blastocyst HRT-FET using exogenous estradiol and vaginal micronized progesterone for endometrial preparation were included.The serum progesterone level was measured in the morning of the FET, in a single laboratory. The two progesterone measurements performed the day of the first (FET1) and the second FET (FET2) were compared to evaluate the intra-individual variability of serum P.Paired statistical analyses were performed, as appropriate.

Main results and the role of chance
Two hundred and sixty-four patients undergoing two consecutive single autologous blastocyst HRT-FET were included. The mean age of the included women was 35.0 ±4.2 years old. No significant intra-individual variability was observed between FET 1 and FET2 (Mean progesterone level after FET1: 13.4±5.1ng/ml versus after FET 2: 13.9±5.0; p = 0.08).Characteristics of embryo transfers were similar between the first and the second FET. Forty-nine patients (18.6%) had discordant progesterone levels (defined as one progesterone measurement &gt; and one ≤ to the threshold of 9.8ng/ml) between FET1 and FET2. 37/264(14%) women had a high intra-individual variability (defined as a difference in serum progesterone values &gt;75 e percentile (6.0ng/ml)) between FET1 and FET2. No specific clinical parameter was associated with a high intra-individual variability nor a discordant P measurements.

Limitations, reasons for caution
This study is limited by its retrospective design. Likewise, only women who underwent autologous blastocyst HRT-FET with micronized vaginal P were included.

Wider implications of the findings
No significant intra-individual variability was showed and the serum progesterone level seems to be reproducible in more than 80% of case. This study suggests that the serum progesterone level measured the day of the first transfer could be used to individualize luteal phase support on subsequent cycles.

Trial registration number
not applicable