Congenital heart disease and pregnancy

By Michael Earing, MD

The incidence of congenital heart disease (CHD) in the United States is estimated to be 0.5-0.8 percent, or 32,000 new cases per year. This does not include bicuspid aortic valves, occurring in 2-3 percent of live births. As a result of medical and surgical advances, 85 percent of children born with CHD now are surviving into adulthood. This has resulted in a steady increase in the number of females with CHD reaching childbearing age. In fact, CHD now is the predominant form of heart disease encountered during pregnancy in developed countries.

CHD does not preclude a successful pregnancy, however the hemodynamic changes that occur during pregnancy can have adverse consequences for the pregnant woman and her fetus. These complications may include heart failure, arrhythmias, stroke and even death of the mother or fetus. During a normal pregnancy, there is a 20-30 percent increase in red blood cell mass and a 30-50 percent increase in plasma volume, resulting in an increase in the total blood volume. In addition, the heart rate increases by 10 beats/minute and there is a reduction in both the systemic and pulmonary vascular resistance. As a result of these changes, the cardiac output steadily increases until the 32nd week, where it plateaus at 30-50 percent above the prepregnancy level. During labor and delivery, there are further hemodynamic changes. With uterine contractions, an additional 300-500 ml of blood can enter the circulation. In addition, the heart rate and blood pressure at the time of labor and delivery also is increased. These changes result in the cardiac output at the time of delivery being nearly 80 percent higher than the prepregnancy level. Immediately following delivery, relief of caval compression results in improved venous return and there will be spontaneous diuresis. However, it will take two-to-four weeks for the hemodynamics to return to baseline.

The task of advising females with CHD in regard to the safety of pregnancy needs to be an intricate part of all adult congenital heart disease and pediatric cardiology programs. Studies of pregnancy outcomes in women with CHD have shown that one can expect a favorable maternal and fetal outcome in most cases. However, because of the hemodynamic changes of pregnancy, certain conditions have been shown to carry significant risk to both the mother and fetus. In general, fixed obstructive cardiac lesions with severe obstruction (mitral and aortic valve stenosis, coarctation of aorta, hypertrophic cardiomyopathy) and those with pulmonary hypertension (defined as pulmonary artery pressure greater than or equal to three-fourths systemic) are poorly tolerated and are considered contraindications to pregnancy. In contrast, regurgitant lesions and lesions with resting left to right shunts in the setting of normal pulmonary artery pressure typically are well tolerated. Other cardiac conditions in which pregnancy should be avoided include class III-IV congestive heart failure due to systemic ventricular dysfunction and Marfan syndrome with a dilated aortic root of 40 mm.

Risk stratification and counseling of women with CHD is best accomplished prior to conception and can be obtained by performing a detailed cardiovascular history and exam, 12-lead ECG and a transthoracic echocardiogram. In counseling, the following six areas need to be considered:

• The underlying cardiac lesion.
• Maternal functional class.
• The possibility of further palliative or corrective surgery prior to conception that may improve hemodynamics such as in the setting of aortic valve stenosis.
• Additional associated risk factors that may complicate a pregnancy such as preexisting arrhythmias, prosthetic valves, chronic anti-coagulation or use of other teratogen drugs such as Ace inhibitors.
• Maternal life expectancy and ability to care for her child.
• The risk of congenital heart disease in the child.

Classically, patients have been stratified into low, intermediate or high-risk groups based on the nature of their lesion. However, over the last 10 years it has become increasingly evident that maternal status defined by New York Heart Association (NYHA) functional class is highly predictive of both maternal and fetal prognosis. In the largest published series, the maternal mortality rate for women in NYHA class I or II with CHD was less than 1 percent. However, with advanced NYHA class, the maternal mortality rate increased to 7 percent. Similarly in this same study, the maternal functional class also was highly predictive of fetal outcome with a fetal mortality for women in NYHA class IV of 30 percent.

Thus, management of pregnant women with CHD depends on both the underlying cardiac condition and their maternal functional class. In general, women considered to have a low risk lesion and who are in NYHA class I prior to pregnancy are followed with fetal ultrasound and fetal cardiac ultrasound and can be safely delivered in a community hospital.

With few exceptions, vaginal delivery with a facilitated second stage of labor (forceps delivery or vacuum extraction) is the preferred route of delivery in patients with CHD. Cesarean delivery is indicated when obstetrics reasons are present, in those patients on coumadin, acute aortic dissection, Marfan syndrome with a dilated aortic root, and those with severe pulmonary hypertension and severe cardiac obstructive lesions. Labor should be conducted in the left lateral decubitus position to attenuate hemodynamic fluctuations associated with contractions. Epidural anesthesia with adequate volume preload is the preferred method of pain control in women with CHD, in particular in patients with single ventricle physiology. The American Heart Association currently does not recommend endocarditis prophylaxis for women with CHD expected to have an uncomplicated delivery. However, many centers with significant experience with CHD and pregnancy continue to recommend endocarditis prophylaxis given it often can be difficult to predict which delivery may become complicated.

Pregnant women with high risk lesions who are in NYHA class III-IV should be managed in a high-risk pregnancy center experienced with CHD by a multidisciplinary team composed of obstetrics, cardiovascular anesthesia, cardiology and pediatrics. Once fetal maturity is confirmed, elective induction of labor often is preferred. Invasive hemodynamic monitoring in these patients with intra-arterial monitoring with or without a central venous catheter often is helpful and allows for rapid intervention if complications arise. In the immediate postpartum period, there continues to be large fluctuations in hemodynamics. As a result, postpartum, these patients should be monitored for a minimum of 72 hours in the hospital.

Women with CHD now comprise the majority of patients with heart disease seen in pregnancy, accounting for 80 percent of all patients. In general, pregnancy is well tolerated in patients with CHD. However, for some women with particularly high-risk lesions and poor functional class, pregnancy poses significant risk for cardiovascular complications including premature death. As a result, pre-conception counseling and risk stratification is mandatory and should be done in all women with CHD of child bearing age.

Michael Earing, MD, is a cardiologist with the Adult Congenital Heart Disease Program of the Herma Heart Center at Children's Hospital of Wisconsin. He also is an assistant professor of Pediatrics (Cardiology) and Internal Medicine at the Medical College of Wisconsin. Member, Children's Specialty Group. 

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