The Division of Epidemiology, Statistics, and Prevention Research requests ultrasound standards for normal fetal growth that includes racially/ethnically diverse women, African-American, Asian, Hispanic, and Whites. Data is also needed on fetal growth trajectories for twins, particularly by chorionicity. The cohort study was The National Standard for Normal Fetal Growth, which enrolled 2,400 low risk pregnant women and 600 obese pregnant women with singleton. Sites included Northwestern University, Medical University of South Carolina, University of California, Womens and Infants Hospital of Rhode Island. There are 585,000 individual ultrasound images acquired. The placenta of intrauterine growth restricted neonates are collected and studied.