Distribution of the Age at First Birth among US Women 1984-1993: An Analysis of a Bimodal Pattern

Rachel Sullivan, University of California, Berkeley

Using both waves (1988 and 1996) of the National Survey of Families and Households, I show that the age at first birth among US women has a bimodal distribution, with peaks near ages 20 and 25. This finding suggests a new interpretation of fertility patterns among US women, namely that there are two entirely separate childbearing regimes which can be identified through age at first birth. Overall, women who have a later first birth have much greater control over their lives and are following distinctly different life course trajectories than those who have an earlier first birth. Given that fertility is closely related to marriage and methods of family strategizing, the existence of differential fertility regimes indicates that there may be a divergence in the means through which the structure of modern families is determined, which is important to our understanding of the family as well as to policy considerations.