ENDOMETRIAL COMPACTION DOES NOT PREDICT CLINICAL PREGNANCY IN SINGLE EUPLOID FROZEN EMBRYO TRANSFERS: A PROSPECTIVE OBSERVATIONAL STUDY

Abstract

To investigate the relationship between endometrial compaction and clinical pregnancy rate (CPR) in euploid frozen embryo transfer (FET) cycles. In this prospective observational study at a large academically-affiliated center, we included patients 18 to 43 years old who had an autologous single euploid FET with ≥7 mm endometrial thickness (EMT) on transvaginal ultrasound (TVUS). We excluded patients with body mass index >40 or <18.5 kg/m2, those using a gestational carrier, a history of ≥2 miscarriages, uterine factors, or a prior endometrial receptivity assay biopsy. All embryos had preimplantation genetic testing for aneuploidy (PGT-A) followed by vitrification at the blastocyst stage. FET protocols consisted of both programmed hormone replacement or natural cycles. We measured the initial EMT (T1) with TVUS within 1 day of initiation of progesterone or ovulation trigger injection. The second EMT (T2) was measured transabdominally at the embryo transfer. Endometrial compaction was calculated as the percent difference in EMT between T1 and T2. All T1 and T2 images were screened by a physician to ensure that the recorded EMTs were accurate. The primary outcome was CPR (gestational sac with fetal heartbeat on ultrasound between 6 to 9 weeks’ gestation). We compared CPR between those with and without compaction at various cutoffs (>0%, ≥5%, ≥10%, ≥15%, and ≥20%) using a chi-square test, and we calculated sensitivity, specificity, and positive negative predictive values of each cutoff. We considered P<0.05 to be statistically significant. The present study was adequately powered according to an apriori calculation. Of the 160 patients included, 75% were undergoing their first FET and 10% had a prior fresh embryo transfer. Only 30.6% patients exhibited any degree of compaction. Compaction was not predictive of CPR at any of the defined cutoffs (Table 1). A sub-analysis stratified by FET protocol type showed similar results. Endometrial compaction was not predictive of clinical pregnancy in single euploid FETs in the overall cohort nor by FET protocol type.