Like so many other parts of health care, childbirth has become a more medically intense experience over the last two decades. The use of drugs to induce labor has become far more common, as have cesarean sections. Today, about half of all births in this country are hastened either by drugs or surgery, double the share in 1990.

Crucial to the change has been a widely held belief that once fetuses pass a certain set of thresholds — often 39 weeks of gestation and five and a half pounds in weight — they’re as healthy as they can get. More time in the womb doesn’t do them much good, according to this thinking. For parents and doctors, meanwhile, scheduling a birth, rather than waiting for its random arrival, is clearly more convenient.

But a huge new set of data, based on every child born in Florida over an 11-year span, is calling into question some of the most basic assumptions of our medicalized approach to childbirth. The results also play into a larger issue: the growing sense among many doctors and other experts that Americans would actually be healthier if our health care system were sometimes less aggressive.

The new data suggest that the thresholds to maximize a child’s health seem to be higher, which means that many fetuses might benefit by staying longer in the womb, where they typically add at least a quarter-pound per week. Seven-pound babies appear to be healthier than six-pound babies — and to fare better in school as they age. The same goes for eight-pound babies compared with seven-pound babies, and nine-pound babies compared with eight-pound babies. Weight, of course, may partly be an indicator of broader fetal health, but it seems to be a meaningful one: The chunkier the baby, the better it does on average, all the way up to almost 10 pounds.