Ultrasound screening of fetal structural abnormalities at 12 to 14 weeks in Hong Kong

Ultrasound screening for fetal abnormalities is conventionally performed at 18 to 20 weeks of gestation. Recent data suggested that many fetal structural abnormalities could be detected by ultrasound examination at 12 to 14 weeks of pregnancy. In this study, we investigated the effectiveness of early ultrasound examination in the detection of fetal abnormalities in women aged 35 years or older.

From February 1998 to March 2001, pregnant women aged 35 or above were examined by transabdominal and transvaginal sonography between 12 and 14 weeks of gestation. If the anatomical survey was normal, the women underwent routine 16- to 20-week ultrasound examination. Pregnancy outcome was obtained from the hospital records or by contacting the subjects.

Twenty-six of the 1609 fetuses had structural abnormalities. Fourteen were detected at the ultrasound examination at 12 to 14 weeks. Detection rate was 53.8% (14/26; 95% CI 44, 64) with a false-positive rate of 0.3% (5/1583; 95% CI 0.16, 0.44). Six additional abnormalities (23.1%, 6/26) were detected at 16- to 20-week ultrasound examination. The overall detection rate of structural abnormalities was 76.9% (20/26; 95% CI 68.6, 85.2).

The effectiveness of ultrasound examination at 12 to 14 weeks to screen for fetal abnormalities approached that achieved at 20 weeks and can be a good adjunct to the conventional examination.