The Dynamics of Prenatal WIC Participation

Year: 2002

Research Center: Institute for Research on Poverty, University of Wisconsin-Madison

Investigator: Swann, Christopher A.

Institution: State University of New York at Stony Brook

Project Contact:
Christopher A. Swann, Assistant Professor
State University of New York at Stony Brook
Department of Economics, SBS S637
Stony Brook, NY 11794
Phone: 631-632-7526


The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) provides food vouchers, nutritional counseling, and health care referrals to low-income pregnant and breastfeeding women and their young children. This study analyzed the characteristics that affect the probability of WIC participation over the course of a woman’s pregnancy. Understanding the program rules and other factors that affect the timing and duration of WIC participation can help to ensure that the program is designed to target resources most effectively.

Although many studies have examined the effect of WIC participation on various health outcomes, relatively little research has focused on the decision to participate in WIC and none have modeled the decision of when to participate. One study provided descriptive information about the month at which participation begins and the number of months of participation, and a number of other studies explored the role of early versus late participation in WIC on birth outcomes. Another recent study, as part of an analysis of health outcomes associated with participation, estimated a simple equation to explain WIC participation.

In this study, the author used data from the 1988 National Maternal and Infant Health Survey, a nationally representative sample of women who experienced a live birth or infant death in 1988, and information about State WIC policies from the 1988 Survey of WIC Program Characteristics. The WIC program data include information on State-level program rules, which varied significantly across the States in 1988. The State-level differences helped the author to assess which program characteristics are important determinants of early participation in WIC.

The study used both parametric and nonparametric hazard rate analysis to examine the relationships among recipient characteristics, WIC program rules, and the timing of WIC participation. These techniques relate maternal, family, and program characteristics to the likelihood that an eligible woman begins participating in WIC during each month of pregnancy, given that she has not participated in the previous months of pregnancy.

The analysis shows that WIC participation is higher among women who have low education levels, are Hispanic, have low income (even among those who are eligible), and participate in other welfare programs. The probability of participating in WIC increases during the first 4 months of pregnancy and decreases thereafter. Women who have participated in WIC during a previous pregnancy are three times more likely to participate in WIC than women who have not participated in the past. The author noted, however, that this result should be interpreted with caution because of limitations on the information in the survey about previous WIC participation.

The study also found that State-level program characteristics are important determinants of WIC participation. Women in States that allow applicants to self-report their income when determining eligibility are 30 percent more likely to participate in WIC than women in States that require applicants to provide documentation of their income. In addition, the State-level policy to offer adjunctive eligibility for WIC to Medicaid and cash assistance recipients is associated with a 10- to 20-percent increase in the likelihood of WIC participation.

Recent policy changes have mandated documentation of income for eligibility determination and have expanded adjunctive eligibility. Given the estimates of this study, these policies have opposite effects on participation. Restricting the ability of applicants to self-declare income decreases the probability of WIC participation, and mandating adjunctive eligibility increases it. The author simulated the effects of these policy changes and found that the net effect is a 1-percentage-point increase in the probability of WIC participation over the course of a 40-week pregnancy.