Perinatal outcomes of resolved fetal cystic hygromas

Cystic hygroma is associated with additional fetal anomalies and genetic abnormalities. Although some cystic hygromas can progress to hydrops fetalis, some regress and resolve with advancing gestation. We aimed to describe the frequency with which cystic hygromas resolve, the prevalence and types of underlying genetic diagnoses, and the differences in perinatal outcomes for resolved cystic hygromas with and without genetic diagnoses.

A retrospective cohort study (2013-2023) at a single tertiary medical center identified fetuses with cystic hygroma diagnosed in the first or second trimester that resolved on subsequent ultrasound imaging. Cystic hygromas were differentiated from increased nuchal translucency by Maternal-Fetal Medicine physicians when a fluid-filled lesion on the posterior neck and back was visualized to have septations or extend beyond the posterior nuchal region superiorly to the cranium or inferiorly. Ongoing pregnancies with prenatal and delivery data were included. We describe perinatal characteristics, genetic evaluations, and neonatal outcomes. Bivariate analyses compared outcomes among fetuses with and without genetic abnormalities. A p value < 0.05 was considered statistically significant.

Of 284 fetal cystic hygromas, 59 (21%) resolved on subsequent imaging and resulted in live birth. The median gestational age at diagnosis was 12.0 weeks [interquartile range (IQR):11.1,12.3] and the latency to resolution was 5.6 weeks (IQR:4.6,8.0). A total of 28 (47%) fetuses had additional ultrasound anomalies, the most common of which were cardiac anomalies. Of 46 individuals who pursued diagnostic genetic testing (45 karyotypes, 30 chromosomal microarrays, and 20 gene panels), 15 (33%) had a genetic abnormality, including aneuploidy (n = 10), pathogenic deletion (n = 2), or single-gene disorder (n = 3). Compared to fetuses with normal genetic testing, fetuses with genetic abnormalities were more likely to have a later gestational age at cystic hygroma diagnosis (12.3 vs. 11.6 weeks, p = 0.007) and resolution (20.1 vs. 17.3 weeks, p = 0.006) in addition to other structural ultrasound anomalies (67% vs. 13%, p = 0.001). A greater proportion of fetuses with resolved cystic hygromas and genetic abnormalities had growth restriction, an earlier delivery, longer neonatal stay, and neonatal complications compared to those with normal genetic evaluation.

The frequency of cystic hygroma resolution in our cohort was 21%. A third of pregnancies who underwent diagnostic genetic testing were found to have an underlying genetic abnormality. Fetuses with genetic abnormalities were more likely to have other structural anomalies and obstetric complications compared to those with normal genetic testing. Providers should maintain a high index of suspicion for genetic conditions or associated anomalies in resolved cases and consider advanced testing even after apparent improvement on ultrasound.