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

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

Reviewer: Gina Humphries |ASA SIG: Women’s Health

Authors: Bet B, Lugthart M, Linskens H, van Maarle M, van Leeuwen E, Pajkrt E

Why the study was performed

Increased nuchal translucency (NT) thickness > 3.5 mm is a known marker for congenital anomalies between 11 and 14 weeks gestation. There is limited understanding of its use as a screening tool before 11 weeks. This study aimed to investigate whether fetuses with an increased NT before 11 weeks are at risk of adverse pregnancy outcomes.

How the study was performed

This was a prospective cohort study that followed 109 women with a viable fetus, an NT measurement ≥ 2.5 mm and a CRL < 45 mm. An NT measurement of < 2.5 mm was considered normal at this scan. All women included in the study were referred to a fetal medicine unit and examined again when the CRL was > 45 mm. The NT was remeasured at this time. Patients were then allocated to one of two groups: those with a normalised NT < 3.5 mm and patients with a persistently increased NT > 3.5 mm. All patients were monitored until 4 weeks postpartum. The study then analysed the association between NT thickness before 11 weeks and adverse outcomes, and compared fetuses with a normalised NT to those with a persistently increased NT at the follow-up scan. Adverse outcomes were defined as aneuploidies and other genetic disorders, including chromosomal aberrations and (mono)genetic diseases.

What the study found

This study found an adverse pregnancy outcome in 35.8% of fetuses with an increased nuchal translucency (NT) thickness ≥ 2.5 mm before 11 weeks. The authors confirmed that fetuses with a persistently increased NT have an elevated risk of adverse outcomes when compared to fetuses with a normalised NT < 2.5 mm (65.2% vs 14.3%). The rate of adverse outcome was significantly reduced in fetuses with a normal NT measurement in the 11 to 14-week scan when compared to those with a persistently increased NT at the follow up scan (14.3% vs 65.2%). Importantly, for fetuses in which the NT normalised, the incidence of adverse outcomes was 8.5%, remaining higher than the baseline risk.

Relevance to clinical practice

This study draws attention to the benefit of evaluating the NT during a scan between 9- and 11-weeks gestation. Fetuses with an early increased NT before 11 weeks are at high risk of adverse pregnancy outcomes. In particular, the risk of chromosomal and structural anomalies remains higher than the baseline risk regardless of whether the NT remains increased or normalises after 11 weeks. Evaluation at this early stage may become routine for sonographers with an increased NT before 11 weeks, prompting a referral to a fetal medicine unit for detailed imaging and counselling about diagnostic and testing options.

“Fetuses with an early increased NT thickness are at considerable risk of an adverse pregnancy outcome, even if the NT normalises after 11 weeks”