Sonographic identification of fetuses with Down syndrome in the third trimester: a matched control study.

OBJECTIVE

To determine sonographic findings in Down syndrome fetuses in the third trimester.

METHODS

Down syndrome fetuses who had third-trimester ultrasound examinations between 25 and 41 weeks' gestation were matched for gestational age with three controls each. Fetal structural anomalies, Down syndrome dysmorphology markers (abnormal facial profile, sandal gap, tongue thrusting, clinodactyly, or hypoplastic middle phalanx of the fifth finger), and abnormal long-bone biometry (femur, humerus, tibia, and fibula; femur length to biparietal diameter ratio; and femur length to abdominal circumference ratio were abstracted from the ultrasound reports. The fetal face, hands, feet, profile, and cardiac outflow tracts are routinely evaluated in our center.

RESULTS

Seventeen fetuses with Down syndrome who had third-trimester ultrasound evaluations were identified. Anomalies included cardiac defects (five), tongue thrusting (three), clinodactyly (three), abnormal profile (three), sandal gap (two), and duodenal atresia (two). Of the 17 fetuses, at least one long-bone abnormality was found in 13, at least one structural or biometric anomaly was found in 15, and at least two abnormal findings existed in 11. Abnormal ultrasound findings, including structural anomalies, short bones, and Down syndrome dysmorphology markers, were more common in cases than in matched controls.

CONCLUSION

At least one abnormal ultrasound finding was present in 15 of 17 fetuses, and abnormal bone measurements or ratios were discovered in 13 of 17. Abnormal long-bone biometry at third-trimester ultrasound should raise the suspicion of fetal Down syndrome.