Congenital Heart Disease in Pregnancy

Dateline: 08/02/98

Pregnancy is one of the physiological conditions that places a considerable burden on the heart, forcing it to work harder for a significantly long period - nine months. While a normal heart is quite capable of taking this extra workload right in its stride, a diseased one may not be able to cope. Different kinds of heart disease may cause different problems during pregnancy. In this series of articles I plan to discuss this topic in depth.

Pregnancy in congenital heart disease patients

Which heart diseases are common during pregnancy ?

Most heart diseases are present even before pregnancy, and become worse - or maybe manifest for the first time - only during gestation. Not many women with congenital heart disease became pregnant until recently. However, the growing number of birth defects treated by surgery since the late 1960's has resulted in an increasing number of women reaching the reproductive age group. In increasing numbers, these women will become pregnant.

Today the commonest birth defects seen during pregnancy are patent ductus arteriosus, atrial septal defects and ventricular septal defects (which together account for 60%). Others like pulmonary valve stenosis, tetralogy of Fallot and coarctation of the aorta make up about 25%. In the near future, we may have to deal with a number of more complex conditions that have been treated surgically.

Maternal Risks

Among the congenital heart diseases, Tetralogy of Fallot carries a risk of 4 to 20% of mortality in the mother. Atrial septal defects are perhaps the safest of all birth defects.

Even with more the serious conditions, obsessional care can reduce the risks considerably. In one report, of 233 women going through 482 pregnancies (8 of these patients had Eisenmenger's syndrome), NO maternal deaths occured !

Fetal Risks

In mothers with congenital heart disease, pregnancy is almost normal in diseases without cyanosis. However, in cyanotic mothers, many problems like severe growth retardation and higher abortion rates arise. For instance, in Tetralogy of Fallot over one half of pregnancies (57%) end in abortion. Because the maternal blood has a very low oxygen content, there is a lower oxygen exchange across the placenta, and the fetus gets lesser oxygen than normal. As a result, the fetus dies or is delivered prematurely. The situation is however reversed after surgical correction is done.

Coarctation of the aorta is another special condition, in which fetal loss is higher than normal (13%) as a result of lower blood flow to the placenta due to the narrowed aorta.

Will the fetus also develop congenital heart disease ?

A question most parents who themselves have birth defects will ask their doctor is "Will my child also have CHD ?" The risk of congenital heart disease in such pregnancies is 2-4 %, which is twice the incidence of heart disease in the general population.

Specific Congenital Heart Defects in Pregnancy

Coarctation of the Aorta (CoA)

Coarctation is a narrowing of the aorta, the major arterial outflow of the heart. This block reduces blood flow to the placenta and the developing fetus. As a result, fetal growth is impaired. In addition, the high pressure in the aorta proximal to the obstruction can cause a partial rupture - also called "dissection" - of the aorta wall, a very serious condition with life-threatening significance. A maternal mortality rate of upto 17% was reported.

Management of the pregnant patient with CoA

In uncorrected CoA, recommendations include

• medical termination of the pregnancy
• surgical repair of the CoA before delivery

Good obstetric care and blood pressure controlling medication control the risk of aortic dissection which is the major cause of morbidity. If the aorta is dilated, cesarian section is preferred for delivery to avoid the risk of dissection that might be brought on by the mother straining in labor.

For more on this topic, read my other articles.

Tricuspid Atresia and the Fontan Operation

Clinical experience in managing pregnancy in the more complex cardiac birth defects is small, but will certainly increase with the increasing survival rates of surgical repair in infancy and childhood. Pregnancy has been reported in patients with tricuspid atresia, both before surgery and after the Fontan operation.

While maternal outcome in these patients depends on her state of health, fetal outcome is related to the degree of cyanosis in maternal blood. One major problem in these pregnancies is the high risk of thrombo-embolism. The mechanism is the sluggish circulation and high viscosity of blood. Prevention of thrombo-embolism is possible by using anti-coagulant (blood thinner) medication throughout pregnancy.

Univentricular heart

In this even more complex syndrome of patients who have only one functioning ventricle, experience is much more limited. Maternal outcome depends on the pulmonary vascular resistance, with severe elevations of resistance resulting in a high maternal mortality. Fetal outcome is dependent on the severity of maternal cyanosis. Oxygen in maternal blood is exchanged across the placenta and supplies the growing fetus. When cyanosis is severe, the oxygen content in maternal blood is low. As a result, the fetus receives lesser oxygen and develops severe growth retardation and asphyxia.

There are few case reports of successful pregnancies in patients with Ebstein's anomaly and in Transposition of Great Arteries after the Mustard operation. Even heart transplant recepients can undergo pregnancy, the problems being more related to managing immunosuppressive therapy rather than cardiac function.

In the next article, we will see how valvular heart disease affects the pregnancy.