False positives in the prenatal ultrasound screening of fetal structural anomalies.

OBJECTIVE

To describe the false-positive diagnoses of prenatal ultrasound screening of fetal structural anomalies.

METHODS

Pregnancies with fetal structural anomalies either detected prenatally in our center or referred to us, were registered, evaluated, and followed-up prospectively by a multidisciplinary Congenital Defects Committee. After postnatal follow-up was completed, cases were assigned as true positives, false positives or false negatives and categorized by anatomical systems. Pregnancies referred with a nonconfirmed suspicion of anomaly were not included. The false-positive diagnoses were analyzed.

RESULTS

From 1994 to 2004, 903 new registry entries of fetuses structurally abnormal at ultrasound with a complete follow-up were included in the Committee database. There were 76 false positives, accounting for 9.3% of all the prenatally established diagnoses. The urinary tract anomalies were the most frequent false-positive diagnoses found (n = 25; accounting for 8.7% of the urinary tract defects), but the genital anomalies showed the higher rate of no confirmation (n = 5; 15.2%). The specific anomalies most commonly not confirmed were renal pyelectasis (n = 9), cerebral ventriculomegaly (n = 9), abdominal cysts (n = 7) and short limbs (n = 7).

CONCLUSION

Several prenatally diagnosed anomalies would benefit from prudent counseling, because they may be normal variants or transient findings.