In 1960, just 5% of all births occurred outside of marriage. By 1970, this share had doubled to 11%, and by 2000 fully one-third of births occurred to unmarried women. Non-marital births continued to rise until the mid-2000s, when the share of births to unmarried women stabilized at around 40%. 16 Not all babies born outside of a marriage are necessarily living with just one parent, however. The majority of these births now occur to women who are living with a romantic partner, according to analyses of the National Survey of Family Growth. In fact, over the past 20 years, virtually all of the growth in births outside of marriage has been driven by increases in births to cohabiting women. 17 Researchers have found that, while marriages are less stable than they once were, they remain more stable than cohabiting unions. Past analysis indicates that about one-in-five children born within a marriage will experience the breakup of that marriage by age 9. In comparison, fully half of children born within a cohabiting union will experience the breakup of their parents by the same age. At the same time, children born into cohabiting unions are more likely than those born to single moms to someday live with two married parents. Estimates suggest that 66% will have done so by the time they are 12, compared with 45% of those who were born to unmarried non-cohabiting moms.