Fetal nuchal translucency in severe congenital heart defects: experiences in Northern Finland

To evaluate the performance of first-trimester measurement of fetal nuchal translucency (NT) in the detection of severe congenital heart defects (CHDs).

During the study period of 1 January 2008 - 31 December 2011, NT was measured in 31,144 women as a part of voluntary first-trimester screening program for Down's syndrome in Northern Finland. NT was measured by personnel trained on the job by the experienced staff. No certification or annual audits are required in Finland. However, the recommendation is that the examiner should perform 200 scans on average per year. Severe CHD was classified as a defect requiring surgery in the first year of life or a defect that led to the termination of the pregnancy. All severe CHDs diagnosed during the study period in Northern Finland could not be included in this study since all women did not participate in the first-trimester screening and some cases were missing important data.

Fourteen (17.7%) out of 79 severe CHDs were found with NT cutoff of 3.5 mm. Amongst the 79 severe CHD cases, there were 17 chromosomal abnormalities. With NT cutoffs of 2.0 and 1.5 mm the detection rates would have increased to 25.3% (n = 20) and 46.8% (n = 37). Using a randomly selected control group of 762 women with normal pregnancy outcomes, false positive rates (FPRs) were calculated. For NT cutoffs of 1.5, 2.0 and 3.5 mm, the FPRs were, 18.5, 3.3 and 0.4%, respectively.

A greater than 3.5 mm NT measurement in the first-trimester ultrasound is an indication to suspect a fetal heart defect but its sensitivity to detect severe CHD is poor. In our study, only 17.7% of severe CHDs would have been detected with an NT cutoff of 3.5 mm.