Decision tree structure for each strategy arm for prenatal screening of congenital heart disease. 4C → MFM, standard screen with second-trimester ultrasound four-chamber view of the heart, with referral to a maternal-fetal medicine (MFM) specialist if abnormal; 4C → card, standard screen with second-trimester ultrasound of the four-chamber view of the heart, with referral to a pediatric cardiologist if abnormal; 4C + outflow → MFM, screen with second-trimester ultrasound four-chamber and outflow views of the heart (read by a non-MFM specialist), with referral to an MFM specialist if abnormal; 4C + outflow → card, screen with second-trimester ultrasound four-chamber and outflow views of the heart (read by a non-MFM specialist), with referral to a pediatric cardiologist if abnormal; MFM 4C + outflow → card, screen with second-trimester ultrasound four-chamber and outflow views of the heart, interpreted by an MFM specialist and referred to a pediatric cardiologist if abnormal; NT + outflow, tiered screen with first-trimester nuchal translucency and referral directly for fetal echocardiography if abnormal; if normal, screen with second-trimester ultrasound four-chamber and outflow views. Fetal echo, universal screen with fetal echocardiography.