# Assessment of fetal endometrial thickness: a key to the prenatal diagnosis of ovarian cysts

## TL;DR

This study shows that measuring fetal endometrial thickness can help accurately diagnose ovarian cysts before birth, improving prenatal care.

## Contribution

The study identifies fetal endometrial thickness as a novel and reliable imaging marker for prenatal ovarian cyst diagnosis.

## Key findings

- Fetal endometrial thickness was significantly greater in ovarian cysts compared to non-ovarian cysts.
- An ultrasound threshold of 1.9 mm for endometrial thickness achieved 100% sensitivity and specificity for diagnosing ovarian cysts.
- Cyst volume was not independently associated with ovarian cyst diagnosis after adjusting for gestational age.

## Abstract

Fetal abdominopelvic cysts are relatively common, but distinguishing ovarian from non-ovarian cysts prenatally remains challenging because morphologic features overlap, and no imaging marker has been validated.

To evaluate fetal endometrial thickness and cyst volume as imaging markers for the prenatal diagnosis of ovarian cysts.

We conducted a single-center, retrospective study of female fetuses with abdominopelvic cysts diagnosed on prenatal ultrasound and/or magnetic resonance imaging (MRI) between January 2010 and December 2024. Two blinded pediatric radiologists independently measured endometrial thickness and cyst volume, with discrepancies resolved by consensus. Postnatal confirmation of diagnosis was obtained through imaging, surgical pathology, or clinical follow-up. Statistical analyses included regression models adjusted for gestational age and receiver operating characteristic (ROC) analysis.

A total of 63 fetuses met inclusion criteria (40 ovarian cysts, 23 non-ovarian cysts) between 21 weeks and 40 weeks of gestation. Fetuses with ovarian cysts underwent ultrasound at later gestational ages than those with non-ovarian cysts (median, 35.0 weeks vs. 27.9 weeks; P<0.001), and MRI showed a similar difference (median, 34.4 weeks vs. 27.9 weeks; P<0.001). Ovarian cysts were associated with significantly greater endometrial thickness on ultrasound (median 3.2 mm vs. 1.3 mm, P<0.001) and MRI (2.2 mm vs. 1.2 mm, P<0.001). Cyst volumes were larger in ovarian cysts (median, 45.4 mL vs. 2.8 mL; P<0.001), although volume was not independently associated with ovarian cyst diagnosis after adjustment for gestational age (P=0.36). Endometrial thickness remained independently associated with ovarian cysts after adjustment for gestational age (ultrasound coefficient, 1.56 [95% CI, 0.84–2.26]; MRI coefficient, 0.81 [95% CI, 0.41–1.21]). ROC analysis demonstrated excellent diagnostic performance, with an ultrasound threshold of 1.9 mm yielding 100% sensitivity and specificity (AUC, 1.00 [95% CI, 1.00–1.00]). In contrast, cyst volume showed only moderate discriminatory ability (AUC, 0.82 [95% CI, 0.71–0.93]).

Fetal endometrial thickness is a robust imaging marker for the prenatal diagnosis of ovarian cysts. Incorporating this parameter into routine prenatal imaging may enhance diagnostic accuracy, guide counseling, and improve perinatal management.