Screening for structural fetal anomalies during the nuchal translucency ultrasound examination

The purpose of this study was to evaluate the ability to screen for structural fetal anomalies during the nuchal translucency (NT) ultrasound examination, without performing a complete anatomic fetal scan, by using the sagittal views of the fetus.

In a prospective study, we evaluated all the suspected structural findings observed during the NT examinations performed in our Division of Maternal-Fetal Medicine in 2004-2005. The purpose of the examination was to screen for fetal chromosome abnormalities by using the fetal NT measurements. However, the sonographers were instructed to pay attention to any abnormality observed while obtaining the sagittal views of the fetus. Other views were not to be obtained and fetal anatomy scan was performed only if a structural fetal anomaly was suspected when viewing the fetus in sagittal planes. When a structural fetal anomaly was suspected, a fetal anatomy scan was performed, and then a diagnosis was established at 14-16 weeks' gestation or later.

We performed 1723 NT examinations during the study period. The sonographers suspected structural fetal anomalies in 22 cases (1.3%), most of them performed between 11.2 and 13 weeks' gestation. Further evaluation of these cases diagnosed 9 fetuses (0.52%) with structural anomalies including: acrania, holoprosencephaly, Dandy-Walker syndrome, cerebellar agenesis, prune belly syndrome, 2 cases of omphalocele, and 2 cases of cleft lip. The NT was abnormal (greater than 3 mm) in only 1 case (omphalocele). None of the additional 8 cases diagnosed with structural anomalies had a positive maternal serum screening result for trisomy 21. Eight of these 9 fetal structural anomalies were sonographically confirmed at 14-16 weeks' gestation and the remaining 1 was confirmed at 20 weeks' gestation. An additional 13 noncardiac structural anomalies were detected in the study group during routine fetal anatomy scan performed at 14-16 or at 18-24 weeks' gestation. Four of these 9 fetal cardiac defects (44%) were diagnosed by an early fetal echocardiography performed for an increased fetal NT.

In addition to chromosomal anomalies and congenital cardiac defects, the NT examination can provide an opportunity to screen for structural fetal anomalies when viewing within the sagittal planes of the fetus. The NT examination can be used as a screening test for those who require an early fetal anatomy scan without performing an additional early anatomy scan to all patients.