O-144 Endometrial production of 17β-estradiol in relation to pregnancy outcome in women undergoing IVF/ICSI
Authors: Stevens Brentjens L B P M , Delvoux B , Den Hartog J E , Morgan F , Baker M B , Moroni L , Van Hoogenhuijze N E , Torrance H L , Broekmans F J M ,   SCRaTCH-2 Study Group, Van Golde R J T , Romano A 
Published: August 2021

Abstract

Study question
Does the endometrial synthesis and inactivation of 17β- estradiol differ between receptive and non-receptive endometrium in women undergoing IVF/ICSI?

Summary answer
The synthesis and inactivation of 17β-estradiol is similar in the endometrium of women who did and did not achieve a clinical pregnancy through IVF/ICSI.

What is known already
Implantation failure of high-quality embryos is a main concern in IVF/ICSI treatment. Blood sex-steroid concentrations do not reflect their corresponding concentrations in endometrial tissue. This is in line with the concept that blood steroids (and precursors) are locally converted to bioactive metabolites and vice versa, by expressing steroid-metabolising enzymes, such as 17β-hydroxy steroid dehydrogenase (17β-HSD). Studies indicate that alterations in intracrinology might modulate endometrial receptivity. We hypothesize that the local 17β-HSD activity during the window of implantation (WOI) differs between pregnant and non-pregnant IVF/ICSI patients.

Study design, size, duration
Case-control study of 40 patients that were recruited in the SCRaTCH study (NL5193/NTR5342), a randomised trial exploring whether ‘endometrial scratching’ in patients with a previous IVF/ICSI cycle failure affects pregnancy outcome in a subsequent IVF/ICSI cycle. For the present investigation, 20 endometrial biopsies from women who achieved clinical pregnancy after fresh embryo transfer (ET) were compared with 20 endometrial biopsies of women that did not conceive after fresh ET.

Participants/materials, setting, methods
Endometrial biopsies and serum were obtained at LH + 5-8 days (urinary test) in a natural cycle, prior to the fresh ET cycle. Cases (negative pregnancy test, n = 20) and controls (clinically pregnant, n = 20) were matched for primary vs. secondary infertility, embryo quality and age. Reduction of estrone to 17β-estradiol (synthesizing 17β-HSDs) and oxidation of 17β-estradiol to estrone (inactivating 17β-HSDs) were determined by high-performance liquid chromatography (HPLC). Results were compared with the Wilcoxon-Mann-Whitney Rank Sum Test.

Main results and the role of chance
Activity of 17β-HSDs responsible for the reduction of estrone to 17β-estradiol (mainly 17β-HSD type 1) was detected in all samples and ranged from 55 to 1864 pmol 17β-estradiol formed/mg protein/24 h. The values obtained from pregnant women (median: 1054) were not significantly different to those obtained from non-pregnant women (median: 997), p = 0.97. The activity of enzymes responsible for the oxidation of 17β-­ estradiol (mainly 17β-HSD type 2) into the less active estrone ranged from 32 to 1731 estrone formed/mg protein/24 h. The values obtained from pregnant women (median: 737) were not significantly different to those obtained from non-pregnant women (median: 624), p = 0.90. The ratio of 17β-HSD type 1:17β-HSD type 2 had a median of 1.63 in the pregnant woman compared to 1.95 in the group of non-pregnant woman (p = 0.57).

Limitations, reasons for caution
The study is pilot in nature and study population is small. Primary and secondary infertility patients were analysed together. A chance phenomenon could have occurred as included women were included after their first IVF/ICSI cycle, hence not every included study person met the criteria for repeated implantation failure (RIF).

Wider implications of the findings
17β-estradiol metabolism takes place during the WOI, controlling the final 17β-estradiol level. Although the present investigation did not show differences between pregnant and non-pregnant women, it remains important to explore if estrogen balance deviations, e.g. in other cycle phases plays a role in clinical conditions such as primary infertility/RIF.

Trial registration number
NL5193/NTR5342