Accuracy of the mid-trimester ultrasound scan in the detection of fetal congenital anomalies in a reference center in Northeastern Brazil.

Objective: To assess the performance of a basic mid-trimester fetal ultrasound scan protocol for the diagnosis of congenital anomalies by calculating its accuracy, sensitivity, and specificity.

Methods: This longitudinal cohort study involved singleton pregnant women recruited at the mid-trimester fetal ultrasound scan through the postnatal evaluation of congenital anomalies. Pregnant women who underwent a routine mid-trimester ultrasound scan for fetal abnormalities at 20-24 weeks of gestation were enrolled in this study. After childbirth, we searched their medical records on gestational outcomes and neonatal examination records, as well as complementary medical examinations, to assess the ultrasound performance in diagnosing congenital malformations.

Results: We included 967 pregnant women in the study population, and prenatal ultrasound scans detected congenital abnormalities in 67 fetuses (6.9%). Among newborns, 54 (5.6%) were postnatally diagnosed with malformations. The overall sensitivity and specificity of the mid-trimester ultrasound scan for congenital malformation detection were 61.1% and 96.3%, respectively, with an accuracy of 94.3% (p < .05).

Conclusion: The mid-trimester ultrasound scan had good accuracy in the detection of congenital malformations, although the overall sensitivity does not support it as the only screening test for anomalies throughout pregnancy.