Is There an Engine of Nonmarital Fertility?

Wu, Lawrence L., and Steven P. Martin
Working paper no. 2002-14


Does a nonmarital birth ignite an “engine” of subsequent nonmarital fertility? Or does a marital first birth serve as a “brake” on subsequent nonmarital fertility? To answer these questions, we compare the pace of subsequent marital and nonmarital childbearing, given a marital or nonmarital first birth, for currently married versus currently unmarried women. We employ parity-specific, competing-risk hazard models that specify the duration, age, and period structure of higher-order marital and nonmarital births occurring between 1970 and 1995, using retrospective marital and fertility histories from the June 1990 and 1995 Current Population Surveys. Our findings provide little support for an “engine” hypothesis. We find that the interval between a nonmarital first and nonmarital second birth is significantly longer than the interval between a marital first and marital second birth for both white and black women, a result that holds across observed demographic characteristics for these women. For higher-order births, our results also run counter to expectations, with some exceptions. For black women, the interval between a nonmarital second and third birth or between a nonmarital third and fourth birth is generally longer than the corresponding intervals between successive marital births, although these differences are rarely statistically significant. Results for white third births follow a similar pattern. The sole exception to these results concern white fourth births, in which we observed a quicker pace of nonmarital childbearing for white women in some demographic subgroups. Thus if there exists an engine of nonmarital fertility, we find evidence for it only for selected demographic subgroups of white women in their progression from a third to a fourth birth. By contrast, our results are uniformly consistent with predictions from a “brake” hypothesis. We find that women who initiate childbearing within marriage but who then experience a marital separation are significantly less likely to have a subsequent birth outside of marriage. This finding holds for black and white women, across all birth orders, and across all demographic subgroups.Taken together, these empirical findings shed light on the evolving linkage between marriage and fertility, which has drawn increasing attention from social scientists and policymakers concerned with the childbearing of poor and sociallydisadvantaged women.