Nuchal translucency measurement and pregnancy outcome in karyotypically normal fetuses

The aim of the study was to evaluate the use of nuchal translucency measurement as a marker of adverse pregnancy outcome in karyotypically normal fetuses.

During the years 1995-99, nuchal translucency (NT) measurement was routinely offered to all women who had their dating scan in our unit. From the data collected, we calculated the 95th and 99th centiles of the NT for a given crown-rump length using regression analysis. The NT measurements were analyzed in relation to pregnancy outcome, especially with regards to miscarriage, intrauterine death and diagnosis of fetal structural abnormalities, after excluding chromosomal abnormalities.

The pregnancy outcome was available in 6650 (89%) of the 7500 pregnancies. In fetuses with an NT over the 99th centile, 17.8% (relative risk 12.2, 95% CI 7.2-20.8) had an adverse pregnancy outcome (miscarriage, intrauterine death, or termination for fetal abnormality) versus 1.5% for those with a normal measurement. The incidence of structural abnormalities, especially heart defects, was significantly increased in the high-NT groups. Three out of 11 fetuses with major cardiac abnormalities had an NT measurement over the 99th centile. The calculated relative risk for major heart defects in fetuses with increased NT was 33.5 (95% CI 9-123).

In the setting of routine antenatal screening, an increased NT measurement is a marker of a high-risk pregnancy even in karyotypically normal fetuses. In addition, the increased incidence of structural abnormalities makes the close follow-up of these pregnancies imperative and should include specialized fetal echocardiography.