Welfare reform has had far-reaching consequences for unmarried women and their children, including effects on their health insurance status. Those who would be receiving cash assistance absent welfare reform may have lower rates of health insurance if they failed to enroll separately for Medicaid (whose rules did not tighten over this time period), or if the new employment they entered did not provide health insurance. Administrative difficulties involved in accessing Medicaid separately from cash welfare may also have been a factor in the short run. Our research uses data from a large and nationally representative household survey that tracks the same individuals over time, the Survey of Income and Program Participation, to examine the effect of welfare reform (AFDC waivers and TANF implementation) on the health insurance status of unmarried mothers with High School completion or less (the population whose health insurance we expect would be affected by the welfare reform, or the "treatment group") in the time period surrounding a particularly important life event, pregnancy. We look at the effects of these policies over the time period 1990--1999, as well as over the time period 1990--2003, to explore the short run vs. long run impact. Our "control group", those who should not be affected by welfare reform itself but are expected to be affected by other national or state events that are happening contemporaneously, consists of married mothers with High School completion or less; the insurance experience of these women is used to control for the other forces that might otherwise lead us to attribute too little or too large an effect to welfare reform. Given the importance of access to health care at all points in the period surrounding and during pregnancy, we look at how welfare reform has affected insurance status before conception, during pregnancy, and after the birth of the child. We find that the Aid to Families with Dependent Children (AFDC) waivers of the 1990s as well as Temporary Assistance for Needy Families implementation have decreased access to Medicaid health insurance, increased access to employer health insurance, and led to a decrease in overall insurance, depending on the point in pregnancy considered and the time period of the study, with the largest effects found in coverage after the birth of a child. These findings have particular implications for the increasing emphasis on preconception and interconception care as a strategy to improve women's and infant's health.