Many tasks can be tackled more quickly now than 50 years ago, but delivering a baby naturally it seems is not one of them, according to a U.S. government study. Compared with the 1960s, U.S. women have in recent years spent two to three hours longer in labor, according to researchers at the U.S. National Institutes of Health, who said the findings suggest doctors may need to rethink the definition of “normal” labor.