We use exogenous variations in fertility due to twin births to measure the impact of an unplanned child on married women's labor supply and earnings.  Although the overall effects of an unplanned birth on labor supply are small, we find significant effects in the years immediately following the unplanned birth, especially in 1970. We estimate that declining fertility explains between 6 and 13 percent of the increase in married women's labor supply between 1970 and 1980. Twin births are also associated with a substantial short-run loss in earnings. This effect persists longer than the labor supply effects, though it does eventually disappear.

Joyce P. Jacobsen is Associate Professor of Economics at Wesleyan University, James Wishart Pearce III is a graduate student at Stanford University, and Joshua L. Rosenbloom is Associate Professor of Economics at the University of Kansas, and a Research Associate of the National Bureau of Economic Research. The authors thank Claudia Goldin, and T. Paul Schultz for their comments on earlier versions of this paper. The work on this paper grew out of an earlier collaboration with Jaisri Gangadharan, and the authors wish to acknowledge their gratitude for her efforts on that earlier research.  The data utilized in this paper were made available by the Inter-university Consortium for Political and Social Research.  The data for the 1970 and 1980 Censuses of Population were originally collected by the U.S. Dept. of Commerce, Bureau of the Census. Neither the collectors of this data nor the Consortium bears any responsibility for the analyses or interpretations presented here. The data used in this article can be obtained beginning January 2000 through December 2003, from Joyce P. Jacobsen, Department of Economics, Wesleyan University, Middletown, CT 06459.