Application of next-generation sequencing in nonimmune hydrops fetalis and its impact on pregnancy decisions

Nonimmune hydrops fetalis (NIHF) has a highly heterogeneous etiology, with genetic factors contributing substantially to its pathogenesis. This study aimed to investigate the chromosomal and monogenic etiologies of NIHF.

This single-center retrospective cohort study included 121 pregnancies complicated by NIHF evaluated at a tertiary referral center between August 2020 and August 2023. All cases underwent copy number variation sequencing (CNV-seq), and 95 additionally underwent whole-exome sequencing (WES), both assays were based on next-generation sequencing (NGS) technology. Cases were stratified according to gestational age at diagnosis, maternal age, conception method, and whether NIHF was isolated or non-isolated. Genetic findings and pregnancy outcomes were analyzed and compared across subgroups, with longitudinal follow-up of pregnancy outcomes.

Among the 121 NIHF cases, pathogenic or likely pathogenic genetic findings were identified in 62 cases, yielding an overall positivity rate of 51.2% (62/121). CNV-seq detected pathogenic abnormalities in 49 cases (40.5%, 49/121), including 38 numerical chromosomal abnormalities and 11 structural chromosomal abnormalities. Among the 95 fetuses that underwent WES, 14 had pathogenic or likely pathogenic variants, corresponding to a positivity rate of 14.7% (14/95). RASopathies (RIT1, RAF1, and BRAF) and skeletal disorders (FGFR2, COL1A1, and HSPG2) were the most frequently identified monogenic conditions. The overall genetic positivity rate was significantly higher in cases diagnosed at ≤ 13⁺⁶ weeks than in those diagnosed at ≥ 14 weeks (61.4% vs. 28.9%, P = 0.001), and in non-isolated NIHF compared with isolated NIHF (58.8% vs. 10.5%, P < 0.001). However, after excluding aneuploidies, no statistically significant differences were observed across clinical subgroups in the detection rates of pathogenic structural chromosomal abnormalities or WES-detected pathogenic/likely pathogenic variants. Cases with positive genetic findings had significantly more adverse pregnancy outcomes than genetically negative cases.

NIHF is associated with a broad spectrum of genetic abnormalities, including aneuploidies, pathogenic structural chromosomal abnormalities, and single-gene disorders. After excluding aneuploidy, the diagnostic yields of pathogenic CNVs and WES were comparable across clinical subgroups. These findings suggest that expanded genomic testing may be valuable across the spectrum of NIHF and may help inform genetic counseling and future pregnancy planning.