Endometrial compaction does not predict live birth in single euploid frozen embryo transfers: a prospective study.

Study Question: Is there a relationship between endometrial compaction and live birth in euploid frozen embryo transfer (FET) cycles?

Summary Answer: Live birth rates (LBRs) were similar in both patients that demonstrated endometrial compaction or no compaction in single euploid FETs.

What Is Known Already: There has been increasing interest in the correlation between endometrial compaction and clinical outcomes but there has been conflicting evidence from prior investigations.

Study Design, Size, Duration: This was a prospective observational study from 1 September 2020 to 9 April 2021.

Participants/materials, Setting, Methods: This study was performed at a single, academically affiliated fertility center in which patients who had an autologous single euploid FET using a programmed or modified natural cycle protocol were included. All embryos had trophectoderm biopsy for preimplantation genetic testing for aneuploidy followed by vitrification at the blastocyst stage. Two ultrasound measurements of endometrial thickness (EMT) were obtained. The first measurement (T1) was measured transvaginally within 1 day of initiation of progesterone or ovulation trigger injection, and a second EMT (T2) was measured transabdominally at the time of embryo transfer (ET). The primary outcome (LBR) was based on the presence and proportion of compaction (percentage difference in EMT between T1 and T2).

Main Results And The Role Of Chance: Of the 186 participants included, 54%, 45%, 35%, 28% and 21% of women exhibited >0%, ≥5%, ≥10%, ≥15% and ≥20% endometrial compaction, respectively. Endometrial compaction was not predictive of live birth at any of the defined cutoffs. A sub-analysis stratified by FET protocol type (n = 89 programmed; n = 97 modified natural) showed similar results.

Limitations, Reasons For Caution: There was the potential for measurement error in the recorded EMTs. The T2 measurement was performed transabdominally, which may cause potential measurement error, as it is generally accepted that transvaginal measurements of EMT are more accurate, though, any bias is expected to be non-differential. The sub-analysis performed looking at FET protocol type was underpowered and should be interpreted with caution. Our study, however, represents a pragmatic approach, as it allowed patients to avoid having to come in for an extra transvaginal ultrasound the day before or on the day of ET.

Wider Implications Of The Findings: Assessing endometrial compaction may lead to unnecessary cycle cancellation. However, further studies are needed to determine if routine screening for endometrial compaction would improve clinical outcomes.

Study Funding/competing Interest(s): No authors report conflicts of interest or disclosures. There was no study funding.

Trial Registration Number: NCT04330066.