Infant Feeding Practices Study II: study methods

Our goal is to describe the methods used in the Infant Feeding Practices Study II (IFPS II), a study of infant feeding and care practices throughout the first year of life. Survey topics included breastfeeding, formula and complementary feeding, infant health, breast-pump use, food allergies, sleeping arrangements, mother's employment, and child care arrangements. In addition, mothers' dietary intake was measured prenatally and postnatally.

The IFPS II sample was drawn from a nationally distributed consumer opinion panel of 500,000 households. All questionnaires were administered by mail, 1 prenatally and 10 postpartum. Qualifying criteria were used to achieve the sample goals of mothers of healthy term and late preterm singleton infants. In addition to the questionnaires about the infants, women were sent a diet-assessment questionnaire prenatally and at approximately 4 months after delivery; this questionnaire was also sent to members of a comparison group who were neither pregnant nor postpartum.

A sample of 4902 pregnant women began the study, and approximately 2000 continued through their infant's first year. Response rates ranged from 63% to 87% for the different questionnaires. Compared with adult mothers of singletons from the nationally representative sample of the National Survey of Family Growth, IFPS II participants had a higher mean education level; were older; were more likely to be middle income, white, and employed; were less likely to smoke; and had fewer other children. Compared with women who participated in the National Immunization Survey who gave birth in 2004, IFPS II mothers were more likely to breastfeed and to breastfeed longer.

The IFPS II provides a valuable database because of its large sample size, the frequency of its questionnaires, and its wide coverage of issues salient to infant feeding.