The study will enroll mothers during week 16-19 of gestation and will ask the mothers to use a hand-held Doppler monitor to listen to the baby's heart rate and rhythm twice daily from about week 16 to week 26 of the pregnancy. Pregnant mothers will be asked to keep a log of the heart rates and will undergo a fetal echocardiogram every 2 weeks during their study participation. In addition to these procedures, the study team will collect the mother's medical and obstetrical histories. Should irregular heart rhythms be detected at home, the mother will contact the investigator to be evaluated. After the baby is delivered, the study team will collect information about the baby's birth and heart rhythm evaluation (electrocardiogram).