O-190 Endometrial compaction in artificial frozen-thawed embryo transfer cycles is associated with improvement in pregnancy outcomes: a meta-analysis
Authors: Oliveira J.B.A , Petersen C.G , Massaro F.C , Petersen B , Vagnini L , Nicoletti A , Ricci J , Zamara C , Oliani A.H , Dieamant F , Franco J.G. 
Published: June 2022

Abstract

Study question
Does the decrease in endometrial thickness between the end of oestrogen phase and embryo transfer day (endometrial compaction) impact the pregnancy outcomes in frozen-thawed embryo transfer (FET) cycles?

Summary answer
The combined data indicated that cycles with endometrial compaction resulted in significantly higher ongoing pregnancy/live birth rate than cycles with no decrease in endometrial thickness.

What is known already
In FET cycles the monitoring of endometrial thickness was mostly concentrated at the end of the endometrium proliferation phase, while research on endometrial thickness in the luteal phase around the embryo transfer day was relatively rare. In addition, few studies have investigated the change in endometrial thickness after progesterone administration, and the conclusions are contradictory. Some studies included women who used hormone replacement therapy for endometrial preparation and showed that endometrial compaction (decreased thickness between the end of oestrogen phase and embryo transfer day) was associated with higher pregnancy rates. However, others reached different conclusions.

Study design, size, duration
A systematic review and meta-analyses was carried out to analyse the effect of endometrial compaction on FET cycle outcomes. The search strategy included online searching of databases (MEDLINE, EMBASE, The Science Citation Index, Google scholar, Cochrane Controlled Trials Register and OVID) up to December 2021. There was no language restriction and included grey literature. The following Medical Subject Headings and text words were used: frozen-thawed embryo transfer, hormonal preparation, endometrial thickness, endometrial compaction.

Participants/materials, setting, methods
Only cycles with artificial endometrial lining preparation (oestrogen-progesterone) and that compared outcomes of endometrial compaction cycles versus no endometrial compaction (no change/increased in endometrial thickness) cycles were considered. The primary outcomes were clinical pregnancy(CPR), miscarriage(MR) and ongoing pregnancy/livebirth (OPR/LBR) rates. The Breslow–Day-statistic, Q-statistic and I² (inconsistency) were used to determine the combinability of the trials. The random effects model was used for odds ratio(OR). The StatsDirect statistical software (Cheshire, UK) was used for data analysis.

Main results and the role of chance
Although endometrial compaction does not significantly affect CPR (OR:1.31[0.91-1.89],P=0.14) and MR (OR:1.18[0.87-1.59];P=0.27, it seems to be associated with a higher OPR/LBR (OR:1.54[1.12-2.13];P=0.007). Table 1 shows the data.

Limitations, reasons for caution
Some trials did not report clinical pregnancy or miscarriage rate. It could be associated with differences in the results. The retrospective nature and lack of standardisation of procedures across studies should be highlighted. Some analyses show high heterogeneity. Although statistically significant, the results in both arms are very close.

Wider implications of the findings
The combined results support the change in endometrial thickness as an easy, low-cost, potential noninvasive marker of endometrial receptivity. However, additional trials are still needed.

Trial registration number
Not applicable