Use of an intensity ratio to describe breastfeeding exclusivity in a national sample

Breastfeeding behavior in a sample of 1863 mother-infant pairs was examined using data from the 1988 National Maternal-Infant Health Survey. Breastfeeding behavior was operationalized as an intensity ratio, calculated as the number of breast milk feeds (on average in 24 hours) divided by the total number of all liquid feeds (on average in 24 hours), with a range from 0 to 1.0. During the first month postpartum, 61% of the sample reported exclusive breastfeeding, declining to 31% during months 2-3 postpartum and to 13% during months 4-6 postpartum. This decline was consistent with the linear decline in the mean intensity ratio, .82, .55, and .31, respectively, during the same three time periods. A higher breastfeeding intensity ratio was significantly associated with longer duration of breastfeeding, up to 1 year of life. Intensity ratio, as a measure of exclusivity, is a useful outcome measure for monitoring breastfeeding behavior.