Early diagnosis of fetal defects

Abnormalities of the heart and great arteries are the most common congenital defects with a birth prevalence of about 8 per 1,000.

• In general, about half are asymptomatic and the other half are classified as major because they are either lethal or they require surgery or interventional cardiac catheterization during the first year of life.
• Major cardiac defects account for about 20% of all stillbirths and 30% of all neonatal deaths due to congenital defects.
• There is a high association between increased NT and cardiac defects in both chromosomally abnormal and euploid fetuses. High NT is not confined to specific types of cardiac defects.
• In euploid fetuses the prevalence of cardiac defects increases with fetal NT from 3 per 1,000 for those with NT between the 5^th and 95^th centiles to 125 for NT of 5.5 mm or more.

Fetal NT above 3.5 mm is found in about 1% of pregnancies. In these cases there is a high risk for cardiac defects and special attention should be placed in the examination of the heart and great arteries both at the time of the NT scan and in subsequent scans at 14-16 weeks and at 20-22 weeks.