In most parts of the United Kingdom, anomaly scanning is offered at 18-23 weeks to check the fetus. One component of such scanning is an assessment of the fetal heart. This usually consists of checking the four main chambers of the fetal heart (atriums and ventricles) and also examining two major vessels (aorta and pulmonary artery) as they leave the heart.
For pregnancies which are judged to be at increased risk for congenital heart disease, then more detailed scans of the fetal heart are typically offered. Such scans are performed by operators with more extensive training in the assessment of the fetal heart.
High risk groups include:
1. Family history of congenital heart disease
If either parent, or a previous child, has had a congenital heart defect then there is an increased risk of subsequent pregnancy being affected. This risk is individualised, but is typically around 2-3%. The type of congenital heart disease which can recur is variable and is not necessarily of the same type or severity as the previously affected individual.
2. Increased nuchal translucency
Nuchal translucency (NT) scans involve measurement of the fluid thickness at the back of the unborn baby's neck. Such scans were introduced to identify fetuses at high risk for chromosomal problems, particularly trisomy 21 (Down syndrome). However, there is a relationship between NT thickness and congenital heart defects, even if the chromosomes of the baby are normal. For this reason, if NT is increased, detailed scans of the fetal heart may be recommended.
3. Maternal drug therapy
Some drugs are known to be associated with congenital heart defects, for example, lithium and some drugs used to treat epilepsy. Your doctor or midwife should be able to advise on this matter.
4. Non-cardiac malformations in the fetus
Some non-cardiac malformations in the fetus are associated with cardiac problems. Examples inlcude abdominal wall defects (exomphalos) or diaphragmatic hernia.
5. Maternal diabetes mellitus
Diabetic mothers are at increased risk of cardiac malformations in the fetus and so such pregnanices are often referred for fetal echocardiography.