Chorionic villus sampling in the cell‐free DNA aneuploidy screening era: careful selection criteria can maximise the clinical utility of screening and invasive testing

Objectives To quantify the impact of cell‐free DNA (cfDNA) screening on chorionic villus sampling (CVS) test indications and outcomes in a tertiary maternity service. Methods Retrospective cohort study of all CVS procedures performed for any indication on singleton pregnancies at The Royal Women's Hospital, Melbourne, and at Women's Ultrasound Melbourne, Australia, between August 2008 and February 2015. Karyotypes were classified according to pathogenicity and detectability by standard cfDNA screening panels. Results A total of 2051 CVS procedures, 25 373 twelve‐week scans and 2394 cfDNA tests were performed. The CVS rate per 12‐week scan fell from 9.8 to 3.9% following introduction of cfDNA screening. The yield of pathogenic chromosomal anomalies per CVS increased from 12.9 to 25.2%, with 70% of pathogenic results now comprising T21, up from 52%. Sixteen (5.3%) of the pathogenic chromosomal abnormalities identified on CVS would not have been predicted by current cfDNA tests. Conclusions There is an evolving tension between improved screening performance for common aneuploidies offered by cfDNA testing, and the increasing diagnostic utility of molecular karyotyping. However, the risk of not identifying pathogenic chromosomal abnormalities is low if cfDNA screening is offered in the absence of a structural fetal anomaly, increased nuchal translucency or relevant family history. © 2017 John Wiley & Sons, Ltd. What is already known about this topic? The improved performance of cell‐free DNA screening in the prenatal identification of common aneuploidies has led to a reduction in rates of invasive prenatal testing A proportion of potentially pathogenic atypical aneuploidies will not be identified by cfDNA screening What does this study add? This large series of CVS procedures in a high‐throughput tertiary centre provides further evidence of the impact of cfDNA screening in reducing CVS rates While the introduction of cfDNA screening has increased the diagnostic yield of each CVS procedure, there is a probable over‐representation of T21 in these late first trimester samples However, the risk of not identifying a pathogenic chromosomal abnormality is low if cfDNA screening is offered in the absence of a structural fetal anomaly, increased nuchal translucency or relevant family history.