the Noonan, Holt-Oram, Williams, and Marfan syndromes and the 22q11 deletion syndrome—the risk is 50%, though penetration and phenotypic expression may vary Specific Cardiac Lesions Left-to-Right Shunts Simple left-to-right shunts—including those produced by an interatrial communication, ventricular septal defect, and patency of the arterial duct—are generally well tolerated during pregnancy The increase in volume load is counteracted to some extent by the fall in peripheral vascular resistance Complications that have been described include arrhythmias, cardiac failure, and paradoxical embolism.17–20 However, these are rare; in a literature review, arrhythmias were reported in only 1 of 123 pregnancies in women with atrial septal defects and in no pregnancies in women with ventricular septal defects No heart failure was reported in either group.21 Atrioventricular septal defects are more complex and can be associated with regurgitation across both the right and left sides of the common atrioventricular junction Compared with women with simple shunt lesions, those with atrioventricular septal defect are more likely to experience cardiac complications.18,22 When intracardiac shunts are associated with pulmonary hypertension, the risk is higher and mainly attributable to the pulmonary hypertension, discussed separately further on Aortic Stenosis and Other Left Ventricular Outflow Tract Lesions A bicuspid aortic valve is the most common cause of an obstructed left ventricular outflow tract in women of childbearing age A smaller number of cases are secondary to subvalvar or supravalvar stenosis or other abnormalities at the valvar level Severe obstruction may not be well tolerated during pregnancy because the increased stroke volume may provoke left ventricular failure Furthermore, the pressure-loaded, marginally compensated, hypertrophied ventricle may poorly tolerate loss of preload or depression of function, so hemorrhage or the effects of general or regional anesthetic agents can lead to hemodynamic embarrassment During pregnancy, women with severe obstruction are at risk for angina, functional deterioration, cardiac failure, and arrhythmias as well as sudden death, although adverse maternal cardiac events are not as common as described in early reports Maternal cardiac complications have been reported in approximately 5% or more of pregnancies.23–26 As many as two-fifths of patients with severe stenosis have required intervention within a few years after pregnancy, so this possibility should be addressed during prepregnancy counseling.26 Balloon aortic valvoplasty and aortic valvar surgery have been performed successfully during pregnancy Because of the risk to the fetus, such interventions should be performed only if there are no other alternatives Despite relatively reassuring maternal outcomes, fetal, neonatal, and obstetric complications are common in women with aortic stenosis Women with moderate or severe aortic stenosis who have been pregnant have higher rates of late complications as compared with women with similar aortic stenosis who have not been pregnant.27 Aortic insufficiency, on the other hand, is generally well tolerated unless it is severe and associated with depressed left ventricular function Aortic Coarctation Most women with coarctation of the aorta have had some type of repair Repair may be associated with late sequelae, such as recoarctation, aneurysms at the repair site—especially when Dacron has been used for a patch—and pseudoaneurysms Thus imaging of the site of repair, usually by magnetic resonance imaging, is optimal prior to conception Patients with unrepaired coarctation or those with repaired coarctation and residual or recurrent obstruction are subject to upper body hypertension Antihypertensive treatment directed at the upper body may exacerbate hypotension distal to the coarctation, and this theoretically could compromise placental perfusion In contemporary studies, maternal mortality in women with repaired coarctation is rare, but women are at increased risk for pregnancy-induced hypertension, preeclampsia, and complications related to the associated bicuspid aortic valve.28–30 Dissection of the aorta has been reported Pulmonary Valvar Stenosis Women with pulmonary valvar stenosis tolerate pregnancy well in spite of the pregnancy-associated increase in preload