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Objectives: An increased nuchal translucency (NT) thickness of ≥ 3.5 mm is a well‐established marker for congenital anomalies and adverse pregnancy outcome between 11 and 14 weeks' gestation, but little is known about its performance as a screening tool before 11 weeks. We aimed to investigate, in a prospective setting, whether fetuses with increased NT before 11 weeks are at risk for adverse pregnancy outcome. Methods: This was a prospective cohort study including pregnant women with a viable fetus with NT ≥ 2.5 mm and a crown–rump length (CRL) < 45 mm. All included women were referred to our fetal medicine unit (FMU) and scheduled for a follow‐up scan where the NT was remeasured after 1 week when the CRL was > 45 mm. Two groups were evaluated: cases with a normalized NT (< 3.5 mm) and cases with persistently increased NT (≥ 3.5 mm). The cases were monitored until 4 weeks after delivery. The main outcome was a composite adverse outcome of aneuploidy, 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. Results: The study included 109 cases, of which 39 (35.8%) had an adverse pregnancy outcome. Of these, 64.1% (25/39) were aneuploid, corresponding to 22.9% (25/109) of the total study population. In the subgroups of NT thickness at inclusion of 2.5–3.4 mm, 3.5–4.4 mm and ≥ 4.5 mm, an adverse outcome was reported in 22.0% (9/41), 40.0% (18/45) and 52.2% (12/23), respectively. In fetuses with a normalized NT and without ultrasound abnormalities at the follow‐up scan, the incidence of adverse outcome was 8.5% (5/59), of which 5.1% (3/59) cases were aneuploid. Conclusions: 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 NT of ≥ 2.5 mm is observed before 11 weeks' gestation. © 2024 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology. This article's abstract has been translated into Spanish and Chinese. Follow the links from the abstract to view the translations. Linked article: There is a comment on this article by Jiang and Li. Click here to view the Correspondence. [ABSTRACT FROM AUTHOR]

This document is a reply to a correspondence regarding a publication in the journal Ultrasound in Obstetrics & Gynecology. The authors agree with the caution expressed by Drs Jiang and Li about adding more scans to the prenatal screening program for congenital anomalies. While their study does not advocate for incorporating nuchal translucency measurements in the early first trimester, they emphasize that an increased nuchal translucency is a marker for congenital anomalies and should not be ignored. The authors recommend prompt referral to a fetal medicine unit for further counseling and diagnostic testing, and suggest that the first- and second-trimester anomaly scans should always be performed in a fetal medicine unit. [Extracted from the article]