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The objective of this study is to determine what percentage of fetal chromosomal anomalies remains undetected when first trimester combined testing is replaced by non-invasive prenatal testing for trisomies 13, 18, and 21. We focused on the added clinical value of nuchal translucency (NT) measurement.Data on fetal karyotype, ultrasound findings, and pregnancy outcome of all pregnancies with an NT measurement ≥3.5 mm were retrospectively collected from a cohort of 25 057 singleton pregnancies in which first trimester combined testing was performed.Two hundred twenty-five fetuses (0.9 %) had an NT ≥3.5 mm. In 24 of these pregnancies, a chromosomal anomaly other than trisomy 13, 18, or 21 was detected. Eleven resulted in fetal demise, and ten showed fetal ultrasound anomalies. In three fetuses with normal ultrasound findings, a chromosomal anomaly was detected, of which one was a triple X.In three out of 25 057 pregnancies (0.01%), non-invasive prenatal testing and fetal ultrasound would have missed a chromosomal anomaly that would have been identified by NT measurement.