Combined first‐trimester screening and invasive diagnostics for atypical chromosomal aberrations: Danish nationwide study of prenatal profiles and detection compared with NIPT

ABSTRACT Objectives Our aim was to examine the prenatal profiles of pregnancies affected by an atypical chromosomal aberration, focusing on pathogenic copy‐number variants (pCNVs). We also wanted to quantify the performance of combined first‐trimester screening (cFTS) and a second‐trimester anomaly scan in detecting these aberrations. Finally, we aimed to estimate the consequences of a policy of using non‐invasive prenatal testing (NIPT) rather than invasive testing with chromosomal microarray analysis (CMA) to manage pregnancies identified as high risk by cFTS. Methods This was a retrospective review of the Danish Fetal Medicine Database of all pregnant women who underwent cFTS and a risk assessment for trisomy 21 between 1 January 2008 and 31 December 2018. Chromosomal aberrations diagnosed prenatally, postnatally or from fetal tissue following pregnancy loss or termination of pregnancy were identified. Chromosomal aberrations were grouped into one of six categories: triploidy; common trisomy (13, 18 or 21); monosomy X; other sex‐chromosome aberration (SCA); pCNV; and rare autosomal trisomy (RAT) or mosaicism. The prevalence of each aberration category was stratified by the individual cFTS markers and trisomy 21 risk estimate, and the size of each pCNV diagnosed by CMA was calculated. Results We retrieved data on 565 708 pregnancies, of which 3982 (0.70%) were diagnosed with a fetal chromosomal aberration. cFTS identified 87% of the common trisomies, but it also performed well in identifying triploidies (86%), monosomy X (92%), atypical SCAs (58%) and RATs or mosaicisms (70%). pCNVs comprised 27% (n = 1091) of the chromosomal aberrations diagnosed overall, and the prevalence increased during the study period, as prenatal CMA was increasingly being performed. In pregnancies with a maternal age