One recognized risk factor is diabetes during pregnancy, including gestational diabetes. When a pregnant person’s blood glucose remains elevated, more glucose can cross the placenta to the developing baby. The baby’s body responds by producing additional insulin, which can encourage increased growth.
This does not mean every person with diabetes will have a large baby, nor does every large newborn have a mother with diabetes. It is simply one factor healthcare professionals consider.
Genetics and family characteristics
Genetics can also influence a baby’s size. Parents who are physically large may have larger-than-average children, although family height and build do not determine birth weight on their own.
Other influences include the baby’s sex, the duration of the pregnancy, and the mother’s health and nutritional circumstances.
Pregnancy duration
A pregnancy that continues beyond its expected delivery date may allow the baby additional time to grow. The relationship is not straightforward, however, and gestational age alone cannot explain every case of extreme birth weight.
