The cumulative impact of WIC participation on birth outcomes was examined in two ways. First, WIC participants and their matched controls were stratified into three groups based on absolute number of months in the WIC program: 33 percent participated for one to three months; 45 percent for four to six months; and 22 percent for seven to nine months. Second, to compensate partially for differing lengths of gestation, participants were also stratified into four groups based on percentage of pregnancy in the WIC program: 32 percent participated for 0-40 percent of their pregnancy; 40 percent participated for 41-70 percent; 20 percent participated for 71-100 percent; and 8 percent had unknown gestations.