What to expect from routine midtrimester screening for congenital heart disease.

The four-chamber view is the standard screening view of the fetal heart. However, it detects only about half of cardiac defects. Because this view does not show the great vessels, only conotruncal abnormalities with substantial septal defects will be seen. Second, septal defects may be too small at the time of screening to be detected. In addition, some defects such as pulmonic stenosis are late appearing. The addition of the aortic outflow tract view increases sensitivity by approximately 20%. Although all components of the four-chamber view may not be seen, there is still considerable information supplied by each of its parts.