Background -Pregnant women with congenital heart disease are at increased risk for cardiac and neonatal complications, yet risk factors for adverse outcomes are not fully defined. Methods and Results -Between January 1998 and September 2004, 90 pregnancies at age 27.7±6.1 years were followed in 53 women with congenital heart disease. Spontaneous abortions occurred in 11 pregnancies at 10.8±3.7 weeks, and 7 underwent elective pregnancy termination. There were no maternal deaths. Primary maternal cardiac events complicated 19.4%of ongoing pregnancies, with pulmonary edema in 16.7%and sustained arrhythmias in 2.8%. Univariate risk factors included prior history of heart failure(odds ratio[OR], 15.5), NYHA functional class ≥2(OR, 5.4), and decreased subpulmonary ventricular ejection fraction(OR, 7.7). Independent predictors were decreased subpulmonary ventricular ejection fraction and/or severe pulmonary regurgitation(OR, 9.0) and smoking history(OR, 27.2). Adverse neonatal outcomes occurred in 27.8%of ongoing pregnancies and included preterm delivery(20.8%), small for gestational age(8.3%), respiratory distress syndrome(8.3%), intraventricular hemorrhage(1.4%), intrauterine fetal demise(2.8%), and neonatal death(1.4%). A subaortic ventricular outflow tract gradient >30 mm Hg independently predicted an adverse neonatal outcome(OR, 7.5). Cardiac risk assessment was improved by including decreased subpulmonary ventricular systolic function and/or severe pulmonary regurgitation(OR, 10.3) in a previously proposed risk index developed in pregnant women with acquired and congenital heart disease. Conclusions -Maternal cardiac and neonatal complication rates are considerable in pregnant women with congenital heart disease. Patients with impaired subpulmonary ventricular systolic function and/or severe pulmonary regurgitation are at increased risk for adverse cardiac outcomes. Background-Pregnant women with congenital heart disease are at increased risk for cardiac and neonatal complications, yet risk factors for adverse outcomes are not fully defined. Methods and Results -Between January 1998 and September 2004, 90 pregnancies at age 27.7 ± 6.1 years were followed in 53 women with congenital heart disease. Spontaneous abortions occurred in 11 pregnancies at 10.8 ± 3.7 weeks, and 7 underwent elective pregnancy termination. There were no maternal deaths. Primary maternal cardiac events complicated 19.4% of all pregnancies, with pulmonary edema in 16.7% and sustained arrhythmias in 2.8%. Univariate risk factors included prior history of heart failure (odds ratio [OR], 15.5), NYHA functional class 2 (OR, 5.4), and decreased subpulmonary ventricular ejection fraction predictors were decreased subpulmonary ventricular ejection fraction and / or severe pulmonary regurgitation (OR, 9.0) and smoking history (OR, 27.2). Adverse neonatal outcomes oc Curred in 27.8% of all pregnancies and included preterm delivery (20.8%), small for gestational age (8.3%), respiratory distress syndrome (8.3%), intraventricular hemorrhage (1.4%), intrauterine fetal demise A subaortic ventricular outflow tract gradient> 30 mm Hg independently predicted an adverse neonatal outcome (OR, 7.5). Cardiac risk assessment was improved by including decreased subpulmonary ventricular systolic function and / or severe pulmonary regurgitation (OR, 10.3 ) in a previously proposed risk index developed in pregnant women with acquired and congenital heart disease. Conclusions -Maternal cardiac and neonatal complication rates are considerable in pregnant women with congenital heart disease. Patients with impaired subpulmonary ventricular systolic function and / or severe pulmonary regurgitation are at increased risk for adverse cardiac outcomes.