Increased fetal nuchal translucency in the first-trimester screening : pregnancy outcomes and a long-term follow-up of children

Background: Increased nuchal translucency (NT) has been used as a screening method for fetal aneuploidies since 1990s. It is also known to be associated with a wide variety of structural defects and genetic syndromes. Long-term studies with a large cohort about the neurodevelopmental outcome of euploid children with increased fetal NT are sparse and the neurodevelopment is worth further study. Aim: The primary aim of this study was to collect data on the pregnancy outcomes, long-term neurodevelopmental and overall outcomes in a large cohort of fetuses with increased NT from singleton pregnancies in order to improve parental counselling. Material: All singleton pregnancies referred to the Department of Fetal Medicine at the Helsinki University Hospital due to increased NT in the first-trimester screening during 2002 2007 were studied. The outcome data were retrieved from hospital databases and national registers. Results: There were 1063 fetuses with increased NT in the first-trimester screening. Abnormal karyotype was observed in 224 fetuses (21%) and adverse pregnancy outcome occurred in 322 (30%). Termination of pregnancy was performed in 209 (20%) and there were 43 (4%) miscarriages and perinatal deaths. Of the 834 euploid fetuses 74 (9%) had structural defects or genetic disorders. Favourable pregnancy outcome became less likely by increasing NT: favourable outcome occurred in 92% in the lowest NT group (95th percentile 3.4 mm) and in 18% in the highest NT group (≥ 6.5 mm). Of the euploid fetuses with normal second-trimester ultrasound examination 96% were healthy at the discharge from the delivery hospital. During the follow-up (mean 6.5 years) neurodevelopmental impairment was detected in 29 (4.2%) and it was severe in 12 (1.7%). Major structural defects, severe neurodevelopmental impairment, or genetic disorders were detected in 54 cases (7%). Conclusion: One in five fetuses with increased NT (≥ 95th percentile) has chromosomal abnormalities and one in ten of the euploid fetuses has structural defects or genetic syndromes. Major health impairment (major structural defect, severe neurodevelopmental impairment, or genetic syndrome) is likely to be detected in 7% of euploid children with increased NT in the first-trimester screening but normal findings in the second-trimester screening. These results are helpful in counselling the parents when increased NT is detected.