The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) has been providing nutritious foods, nutrition education, breastfeeding support, and health referral services to low-income mothers and their children for over 30 years. In 2006 the Food and Nutrition Service (FNS) asked the Institute of Medicine (IOM) to review the WIC food packages. The IOM proposed major changes to improve nutrition and encourage breastfeeding but also expressed the concern that changes related to partial breastfeeding may have unintended consequences. The IOM recommended that FNS conduct an impact study evaluating the birth month breastfeeding changes to the WIC food packages. This study responds to that recommendation.