A Novel Case of <i>NOTCH1</i> Variant and Nonimmune Hydrops Fetalis: A Case Report

Nonimmune hydrops fetalis (NIHF) refers to the pathologic accumulation of fluid within the fetus due to causes other than red cell alloimmunization and now accounts for up to 90% of fetal hydrops cases. Fetal hydrops is associated with significant morbidity and mortality, and the exact prognosis is largely dependent on the underlying etiology. The most common etiologies include cardiovascular causes and chromosomal or genetic abnormalities. Despite this, diagnostic testing with karyotype or chromosomal microarray only identifies approximately 25% of cases, and up to 20% of cases remain idiopathic or unknown. We report the first known case of NIHF related to a <i>NOTCH1</i> pathogenic variant. In this case, NIHF was diagnosed at 30 weeks' gestation in a fetus with low-risk prenatal genetic screening, noncontributory anatomic survey, and normal chromosomal microarray. The hydrops was uniquely localized to scalp edema and pleural effusions requiring bilateral thoracentesis and never progressed to involve pericardial effusion or ascites. Whole exome sequencing diagnosed a novel pathogenic variant in the <i>NOTCH1</i> gene. This is the first reported case of NIHF in the setting of <i>NOTCH1</i> pathogenic variant and is an important addition to the existing literature on this incredibly diverse, high-risk pathology.