In the U.S., one of the richest countries in the world, the number of babies born too early keeps going up—and with all their medical savvy, doctors can't figure out why. Today nearly 13 out of every 100 births are premature, an increase of 30% over the past 20 years. Part of that rise is due to the advent of modern fertility treatments, which caused a sharp jump in the number of twins, triplets and higher multiples—most of whom are born early. But it turns out that 83% of preemies in the U.S. are singletons whose prematurity can be caused by any number of factors, including bacterial infections, ruptured membranes, cervical abnormalities, high blood pressure, stress, inflammation and the effects of smoking and alcohol consumption.
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