Fetal hydrops and the Incremental yield of Next generation sequencing over standard prenatal Diagnostic testing (FIND) study: prospective cohort study and meta-analysis.

OBJECTIVES Determine the incremental yield of next generation sequencing (predominantly exome sequencing (ES)) over quantitative fluorescence-polymerase chain reaction (QF-PCR) and chromosome microarray analysis (CMA)/karyotyping in; (i) all cases of prenatally diagnosed non-immune hydrops fetalis (NIHF); (ii) isolated NIHF; (iii) NIHF associated with additional structural anomalies and; (iv) NIHF according to severity (i.e., two cavities versus three or more cavities affected). METHODS A prospective cohort study (from an extended group of the Prenatal Assessment of Genomes and Exomes (PAGE) study) of n=28 cases of prenatally diagnosed NIHF undergoing trio ES following a negative QFPCR and CMA/karyotype was combined with a systematic review of the literature. Electronic searches of relevant citations from MEDLINE, EMBASE and CINAHL and clinicaltrials.gov (January 2000 - October 2020) databases was performed. Studies included were those with: (i) ≥ n=2 cases of NIHF undergoing sequencing; (ii) testing initiated based on prenatal ultrasound-based phenotype and; (iii) a negative CMA/karyotype. PROSPERO Registration No. CRD42020221427. RESULTS The PAGE cohort study noted the additional diagnostic yield of ES was 25.0% (n=7/28) for all NIHF, 21.4% (n=3/14) for isolated NIHF and 28.6% (n=4/14) for non-isolated NIHF. From the meta-analysis, the pooled incremental yields from n=21 studies (n=306 cases) were 29% (95% CI 24-34%, I2 =0%, p<0.00001) in all NIHF, 24% (95% CI 16-33%, I2 =0%, p<0.00001) in isolated NIHF and; 38% (95% CI 28%-48%, I2 =6%, p<0.00001) in NIHF associated with additional anomalies. In the latter, congenital limb contractures were the most prevalent additional structural anomaly at 17.3% (n=19/110). Incremental yield did not differ significantly based upon hydrops severity. The commonest genetic disorders identified were RASopathies in 30.3% (n=27/89), most commonly due to PTPN11 variants in 44.4% (n=12) and the predominant inheritance pattern was autosomal dominant in monoallelic disease genes 57.3% (n=51/89), of which most were de novo 86.3% (n=44). CONCLUSIONS Use of prenatal next generation sequencing in both isolated and non-isolated NIHF should be considered in developing clinical pathways. Given the wide range of potential syndromic diagnoses and heterogeneity in prenatal phenotypes of NIHF, exome or whole genome sequencing may prove to be a more appropriate testing approach than a targeted gene panel testing strategy. This article is protected by copyright. All rights reserved.