Granted there isn't a ton of room in the womb for exercise, but what causes some babies—like the 16-pound boy born in Texas—to grow so large? Gestational diabetes in pregnant mothers could be a major cause, reports the Los Angeles Times. It picks up on an explainer from the American Diabetes Association that lays out the chain of events. Baby ends up with high blood glucose levels, and its pancreas makes extra insulin in response.
"Since the baby is getting more energy than it needs to grow and develop, the extra energy is stored as fat," says the ADA. Although the number of big births—babies heavier than 8 pounds, 13 ounces—is actually on the decline in the US, those infants are at an increased risk of developing diabetes and obesity. (Read more childbirth stories.)