PurposeNoninvasive prenatal screening (NIPS) using cell-free DNA in maternal blood is highly sensitive for detecting fetal trisomies 21, 18, and 13. Using a genome-wide approach, other chromosome anomalies can also be detected. We report on the origin, frequency, and clinical significance of these other chromosome aberrations found in pregnancies at risk for trisomy 21, 18, or 13.MethodsWhole-genome shallow massively parallel sequencing was used and all autosomes were analyzed.ResultsIn 78 of 2,527 cases (3.1%) NIPS was indicative of trisomy 21, 18, or 13, and in 41 (1.6%) of other chromosome aberrations. The latter were of fetal (n = 10), placental (n = 22), maternal (n = 1) or unknown (n = 7). One case lacked cytogenetic follow-up. Nine of the 10 fetal cases were associated with an abnormal phenotype. Thirteen of the 22 (59%) placental aberrations were associated with fetal congenital anomalies and/or poor fetal growth (<p10), which was severe (<p2.3) in six cases.ConclusionGenome-wide NIPS in pregnancies at risk for trisomy 21, 18, or 13, reveals a chromosomal aberration other than trisomy 21, 18 or 13 in about one-third of the abnormal cases. The majority involves a fetal or placental chromosome aberration with clinical relevance for pregnancy management.Genet Med advance online publication, 2 October 2017; doi:10.1038/gim.2017.132.