- A pregnant woman initiating prenatal care between 6 0/7 weeks and 16 0/7 weeks estimated gestational age (EGA) by reliable last menstrual period (LMP) or ultrasound. All participants must have confirmation of pregnancy viability (by Doppler or ultrasound) prior to study enrollment. All participants must, by 24 weeks gestation, have ultrasonographic confirmation of a single viable intrauterine pregnancy with no major anomalies.