The Participants: Women and Their Infants
Approximately 4,000 pregnant women from across the nation began their participation in the Infant Feeding Practices Study II (IFPS II) between May and December 2005. The success of the research depended upon a high level of participation by the selected women over the course of 15 months. To maximize participation rates, the study selected the sample from a national consumer opinion panel consisting of 500,000 households from throughout the United States. Between March and June of 2012, FDA and CDC conducted the Year 6 Follow-Up Study (Y6FU) to characterize the health, development, and diet quality of children who participated in the IFPS II. To qualify for the IFPS II, a healthy woman must have given birth to a singleton, full-term, or near-term infant weighing at least 5 pounds at birth. About 2,000 qualified and continued their participation through their baby's first year for IFPS II. To qualify for Y6FU, the mother had to have answered at least the prenatal and neonatal IFPS II questionnaires and not disqualified afterwards. Of 2,958 mothers who qualified for Y6FU based on IFPS II, 1,542 women participated in the follow-up study yielding a response rate of 52.1%.
With the exception of a brief telephone interview near the time of the infant's birth, all IFPS II data were collected using mailed questionnaires. A subset of women in the sample were asked to complete a modified Diet History Questionnaire prenatally and about 4 months postpartum, adapted from one developed by the National Cancer Institute, National Institutes of Health. For comparison purposes, the same dietary information was collected from a sample of women of child-bearing age who are neither pregnant nor post-partum. For Y6FU, two methods were used to collect the data in order to maximize the response rate. Mothers were first sent a questionnaire through the mail, those who did not response after two attempts of mailed questionnaires were contacted to obtain the same information by telephone interview.