For decades, the number of American babies born too small was on the decline. But new data suggests the rate may be ticking up again—especially among African Americans. The World Health Organization defines an underweight newborn as weighing less than 5 pounds, 8 ounces. In 2016, according to new joint report from the Robert Wood Johnson Foundation and the University of Wisconsin Population Health Institute’s annual county health rankings, 8.2 percent of new babies failed to exceed the threshold.