Adverse pregnancy outcome in fetuses with early increased nuchal translucency: prospective cohort study.

Abstract

An increased nuchal translucency (NT) ≥3.5mm is a well-established marker for congenital anomalies and adverse pregnancy outcome between 11 and 14 weeks of gestation. Little is known about its performance as a screening tool before 11 weeks of gestation. We aimed to investigate in a prospective setting whether fetuses with an increased NT before 11 weeks of gestation are at risk for an adverse pregnancy outcome. This is a prospective cohort study including pregnant women with a viable fetus with a NT≥2.5mm and a crown-rump-length (CRL) <45mm. All women were referred to our fetal medicine unit (FMU) and scheduled for a follow-up scan where the NT was remeasured after one week when the CRL was >45mm. Two groups were evaluated: cases with a normalized NT(<3.5mm) and cases with a persistently increased NT (≥3.5mm). We monitored the cases until four weeks after delivery. The main outcome was a composite adverse outcome of aneuploidies, other genetic disorders, structural anomalies and pregnancy loss. We performed subgroup analyses of NT thickness at inclusion and normalized or persistently increased NT at follow-up. We included 109 cases of which 35.8% (39/109) had an adverse pregnancy outcome. Of these 64.1% (25/39) were aneuploidies which corresponds to 22.9% (25/109) aneuploidies in total. The subgroups of NT thickness at inclusion of 2.5-3.4, 3.5-4.4 and ≥4.5mm showed abnormal outcomes in 22.0% (9/41), 40.0% (18/45), 52.2% (12/23) respectively. In fetuses with a normalized NT and without ultrasound abnormalities at follow-up scan, the incidence of adverse outcome was 8.5% (5/59), of which 5.1% (3/59) were aneuploidies. Fetuses with an early increased NT thickness are at considerable risk of an adverse pregnancy outcome, even if the NT normalizes after 11 weeks. Not all congenital anomalies can be diagnosed with routine first-trimester screening such as non-invasive prenatal testing and/or a first-trimester anomaly scan. Therefore, expectant parents should always be referred to a FMU for detailed ultrasonography. Invasive prenatal testing should be offered if an increased nuchal translucency of ≥2.5mm is observed before 11 weeks of gestation. This article is protected by copyright. All rights reserved.