Gravid diseases are complications in pregnancy. They include gestational diabetes and preeclampsia. These can cause problems with how a fetus grows. Being pregnant with twins can make complications more likely. Research suggests that changes in fetal soft tissue may be the earliest signs of growth problems. These tissue changes are in lean mass, fat mass, and organ size. 3D images might detect these changes earlier than 2D images. This could help manage gravid diseases. The NICHD Fetal Growth Studies - Singletons measured fetal growth for four racial groups, Caucasian, African American, Asian, and Hispanic. Fetuses of obese women and women with twins were also measured. 2D and 3D images were taken at various stages of pregnancy. Measurements were taken after birth. Researchers want to expand this study by measuring organ volumes and body composition by racial group and in twins.