The prevalence of heart disease in pregnant women is estimated to be between 0.1 and 4%; although the prevalence has not changed for decades, the relative contribution of different types of heart disease varies according to the study population and the study period. Nowadays, in developed countries the largest group of females with an underlying heart disease consists of women with congenital heart defects (70–80%), followed by patients suffering from valvular sequelae of rheumatic fever.¹ Congenital heart defects occur in approximately 0.8% of newborns. Progress in medical, interventional, and surgical treatment has largely improved the outcome for these children, leading to an excellent survival into adult life.^2–4 In particular, congenital aortic valve stenosis (AS) accounts for about 5% of all congenital heart defects. Despite a male predominance (the male–female ratio is between 3:1 and 5:1), AS is considered to be the most common cause of left ventricular outflow tract (LVOT) obstruction in young women. These women reach reproductive age and want to become pregnant. Unfortunately, underlying heart disease has become the major cause of non-obstetrical maternal death and accounts for 15% of all pregnancy-related mortality in Western countries.^5,6 The level of risk incurred by pregnancy depends on functional status and the specific cardiac condition, both of which determine the ability of the cardiovascular system to adapt to the physiological changes of pregnancy.

Morphological, Epidemiological, and Hereditary Aspects of Congenital Aortic Stenosis

Congenital obstruction of the LVOT may involve the subvalvular, valvular, or supravalvular part of the outflow tract complex. Stenosis due to a congenital malformation of the aortic valve is the most common form of LVOT obstruction, found in more than 50% of cases. Abnormal development of the valve commissures results in unicuspid, bicuspid, tricuspid, or even quadricuspid valves. The most common abnormality is the bicuspid valve, which accounts for more than 95% of congenital AS. A bicuspid valve seems to be an isolated defect, but in 20% of patients associated defects can be found, including coarctation of the aorta (most common), patent ductus arteriosus, and ventricular septal defect (VSD). Moreover, a bicuspid valve is found in approximately 50% of patients with coarctation of the aorta. These two lesions are the most common cardiac anomalies found in patients with Turner syndrome. In about one-third of patients, the level of the obstruction is subvalvular. Subvalvular stenosis represents a spectrum of anomalies ranging from a simple fibrous membranous to a tunnel-like fibromuscular band. It can be found as an isolated lesion, but in 60% of cases it is related to other heart defects, particularly to multilevel LVOT obstruction. Other associated lesions include VSD, coarctation of the aorta, and the Shone complex (coarctation of the aorta, parachute mitral valve, supravalvular mitral ring, sub-AS).

Finally, supravalvular AS is found to be the rarest obstructive lesion of the LVOT (less than 10%). The defining feature of this condition is aortic narrowing above the level of the aortic valve. In more than one-third of cases, the aortic valve is also abnormal; association with a subvalvular obstruction (20% of cases), coarctation of the aorta, and mitral valve stenosis. It appears uncommon as an isolated defect and is mostly found as a mild form when detected during adulthood. More often, a supravalvular stenosis in adults is encountered as a residual lesion following surgical repair in childhood, or as one of the characteristics of Williams syndrome (60% of cases). Supravalvular stenosis might also occur in familial form (7%) and even sporadically (30%).

Mothers with congenital heart defects have an approximately 6–8% risk of passing them on to their children—a 10-fold increase in comparison with the general population, which is probably due to multifactorial inheritance.7 However, in the case of a monogenetic anomaly such as Williams syndrome and some familial forms of supra-aortic stenosis, an autosomal dominant pattern is present, affecting 50% of the offspring. Therefore, genetic counseling should be incorporated when discussing child wish.

Pathophysiological Changes During Pregnancy and Labor

In normal pregnancy, both plasma volume and cardiac output increase steadily until the end of the second trimester, when cardiac output reaches its plateau at 30–50% above pre-pregnancy levels^.8,9 A higher stroke volume and, to a lesser extent, an increase in heart rate (up to ^10–15 beats per minute) are responsible for the increase in cardiac output. Simultaneously, systemic vascular resistance and blood pressure decrease. The latter usually lowers to its nadir at about 20 weeks‘ gestation, and returns to pre-pregnancy levels at term. In severe AS, stroke volume remains fixed and the increase in cardiac output is strongly limited, which leads to an elevation of ventricular systolic and diastolic filling pressures. These patients become very sensitive to acute changes in preload and afterload, so that myocardial ischemia and heart failure can occur.