Routine ultrasound examination at 12 or 18 gestational weeks for prenatal detection of major congenital heart malformations? A randomised controlled trial comprising 36,299 fetuses

Abstract

Objective: To compare the rate of prenatal diagnosis of heart malformations between two policies of screening for heart malformations.

Design: Randomised controlled trial.

Setting: Six university hospitals, two district general hospitals.

Sample: A total of 39 572 unselected pregnancies randomised to either policy.

Methods: The 12-week policy implied one routine scan at 12 weeks including measurement of nuchal translucency (NT), and the 18-week policy implied one routine scan at 18 weeks. Fetal anatomy was scrutinised using the same check-list in both groups, and in both groups, indications for fetal echocardiography were ultrasound findings of any fetal anomaly, including abnormal four-chamber view, or other risk factors for heart malformation. In the 12-week scan group, NT >or=3.5 mm was also an indication for fetal echocardiography.

Main outcome measure: Prenatal diagnosis of major congenital heart malformation.

Results: In the 12-week scan group, 7 (11%) of 61 major heart malformations were prenatally diagnosed versus 9 (15%) of 60 in the 18-week scan group (P= 0.60). In four (6.6%) women in the 12-week scan group, the routine scan was the starting point for investigations resulting in a prenatal diagnosis versus in 9 (15%) women in the 18-week scan group (P=0.15). The diagnosis was made <or=22 weeks in 5% (3/61) of the cases in the 12-week scan group versus in 15% (9/60) in the 18-week scan group (P=0.08).

Conclusions: The prenatal detection rate of major heart malformations was low with both policies. The 18-week scan policy seemed to be superior to the 12-week scan policy, although the differences in prenatal detection rates were not statistically significant.