879: Utility of Chromosomal Microarray in Cases of Non-Immune Hydrops Fetalis

Chromosomal microarray (CMA) is recommended for evaluation of fetal structural anomalies. The utility of CMA in nonimmune hydrops fetalis (NIHF), however, is not well known. We aim to establish the overall yield of CMA in NIHF, and compare the yield between isolated cases and those associated with structural anomalies. This was a retrospective cohort study of all patients with prenatally diagnosed NIHF seen at the University of California, San Francisco from 2008 to 2018. NIHF was defined as 2 or more of: ascites, skin edema, pleural effusions, pericardial effusions. Cases of twin-twin transfusion syndrome or Rh isoimmunization were excluded. Data on concurrent structural anomalies was extracted, including: central nervous system; face and neck; pulmonary and thoracic; cardiovascular; gastrointestinal; genitourinary; skeletal systems; sacrococcygeal teratomas; and placental causes. CMA results were categorized as normal/likely benign, variant of uncertain significance (VUS), or pathogenic/likely pathogenic. Fisher’s exact test was used to compare proportions. There were 132 cases of prenatally diagnosed NIHF. Thirty-six (27.3%) cases were isolated NIHF and 96 (72.7%) cases had at least 1 major structural anomaly. A CMA was performed in 45 cases, including 15/36 (41.7%) isolated and 30/96 (31.3%) with structural anomalies (p=0.26). In 44/45 (97.8%) cases with CMA performed, results were categorized as normal/likely benign. There were no VUS not identified as likely benign or likely pathogenic, and the only pathogenic variant identified was trisomy 21. Among a cohort of prenatally diagnosed NIHF cases, CMA did not identify any copy number variants beyond those detectable by karyotype. These results suggest that CMA has low diagnostic utility in NIHF, regardless of structural anomalies.