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.

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 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 <= 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