Cohabiting mothers are spurring increases in out-of-wedlock births, now at a high of 41 percent. In all, about 60 percent of all births during the 2000s were to married mothers, compared to 24 percent to cohabiting mothers and 16 percent to non-cohabiting mothers. That was the first time that cohabiting births exceeded births from single mothers who weren't living with their child's father.

Since the early 1990s, the share of out-of-wedlock, cohabiting births has grown from 11 percent to 24 percent, while those to non-cohabiting, single mothers has remained steady at 16 percent.