Genomic abnormalities in apparently isolated polyhydramnios and the role of confirmed fetal phenotype: a systematic review and meta-analysis.

Objective: The aim of this systematic review and meta-analysis was to assess the rate of genomic abnormalities detected in pregnancies with apparently isolated hydramnios and explore the role of confirmed fetal phenotype.

Data sources: PubMed, Cochrane Library, Google Scholar and Scopus databases were searched up to May 4, 2024.

Study eligibility criteria: Observational studies, published after the year 2000 and written in a European language, reporting on the genomic outcome of pregnancies complicated with prenatally diagnosed isolated polyhydramnios were included in this meta-analysis.

Study appraisal and synthesis methods: The main outcome was the incidence of genomic abnormalities, defined as chromosomal numerical or structural anomalies or monogenic syndromes, diagnosed prenatally or postnatally in neonates from pregnancies complicated with isolated polyhydramnios. Additional outcomes included the incidence of chromosomal abnormalities including both numerical and structural aberrations of the chromosomes (detected by karyotype/chromosomal microarray [CMA]), monogenic abnormalities (detected by next-generation sequencing [NGS] or clinical genetic examination after the result of a normal karyotype/CMA), genetic syndromes in general (diagnosed clinically with or without genetic confirmation), and structural abnormalities detected postnatally. Pooled proportions were calculated for each outcome.

Results: Twelve studies (2561 pregnancies complicated with isolated hydramnios) were included in the meta-analysis. The pooled prevalence of genomic anomalies in fetuses with apparently isolated polyhydramnios (12 studies, 2634 fetuses) was 4.5% (95%CI 2.6-7.6). The pooled prevalence of chromosomal abnormalities (11 studies, 2427 fetuses) was 2.1% (95%CI 1.1-3.7). The proportion of major structural defects detected postnatally (9 studies, 1731 fetuses) was 2.9% (95%CI 1.5-5.4); in this particular subgroup (4 studies, 14 fetuses), the pooled prevalence of genomic anomalies was 29.8% (95%CI 11.3-58.6). A meta-regression analysis indicated that the rate of genomic anomalies was positively associated with the severity of hydramnios. Also, the pooled rate of monogenic anomalies was 5.6% (95%CI 2-5; I² =58%) in the two studies using NGS for genomic diagnosis.

Conclusions: This meta-analysis showed that the rate of genomic anomalies in apparently isolated polyhydramnios is 4.5%; approximately half of them are chromosomal abnormalities and the other half are non-chromosomal genomic anomalies. From a clinical standpoint, CMA and possibly NGS could be considered even in cases of apparently isolated polyhydramnios; this may be even more important in cases of incomplete fetal phenotype. Further studies using NGS and addressing cost-effectiveness issues would fine-tune such recommendations.