The authors analyzed data from an earlier study of more than 2,600 singleton pregnancies, which included information on maternal weight before and during pregnancy and three-dimensional (3D) ultrasound scans (up to five) throughout pregnancy. The authors found that pregnant people with excessive weight gain — defined as more than 2 kilograms (about 4.4 pounds) in the first trimester — had fetuses with larger abdominal circumference and abdominal area and larger fetal arm fat thickness, when compared to pregnant people with adequate weight gain.

Fetuses from the excessive weight gain group continued to have greater arm thickness and abdominal measurements through the end of pregnancy, even when weight gain was not considered excessive during the second and third trimesters. In contrast, most previous studies have not examined fetal 3D measures during pregnancy and have only linked total weight gain across pregnancy, not just in the first trimester, with birthweight.

The authors wrote that their findings suggest that the timing of weight gain, instead of total weight gain, could be important for developing efforts to prevent excess fetal size and reduce the risk of heart disease and other conditions later in life.