Detection of fetal structural anomalies in a basic first-trimester screening program for aneuploidy.

Objectives: The purpose of this study was to determine whether first-trimester aneuploidy screening sonography initially performed by credentialed sonographers was useful for detecting fetal anomalies between 11 and 14 weeks' gestation.

Methods: We conducted a retrospective cohort study of consecutive patients referred to a private ultrasound facility between January 1, 2008, and June 30, 2012, for measurement of the nuchal translucency (NT) and crown-rump length as part of a screening protocol for aneuploidy. Patients were included if there was at least 1 live fetus with a crown-rump length between 34 and 84 mm. No specific anatomic imaging protocol was followed. The presence of anomalies was based on the sonographic report and review of the medical record. The absence of anomalies was based on the report from the anatomic survey. Anomalies were categorized as lethal, major, and minor. The anomaly category and gestational age at diagnosis (≤14 versus >14 weeks) were compared.

Results: An NT scan was performed on 9692 fetuses. Anatomic surveys were done on 9077 (93.7%) of these fetuses at a mean of 18 weeks' gestation. Anomalies were detected in 180 fetuses (1.8%): 50 (0.5%) at the NT scan and 130 (1.3%) at the anatomic scan. Overall, 46 of 111 fetuses (41.4%) with major or lethal anomalies were detected at the NT scan. Two suspected abnormalities at the NT scan were not present at the anatomic scan.

Conclusions: First-trimester aneuploidy screening sonography initially performed by credentialed sonographers can identify a substantial proportion of major and lethal anomalies.