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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. Women who volunteer to participate in opinion surveys were more likely to comply with the lengthy requirements of the IFPS II than were women chosen randomly from the U.S. population.

While the study began with 4,000 pregnant women, about 2,000 qualified and continued their participation through their baby's first year. To qualify, a healthy woman must have given birth to one healthy, full-term or near-term infant weighing at least 5 pounds at birth.

With the exception of a brief telephone interview near the time of the infant's birth, all 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 were neither pregnant nor post-partum.

The Questionnaires

The Neonatal Questionnaire was sent to the mother when her infant was approximately three weeks old. This questionnaire examined factors that commonly occur near the time of the birth and that may affect infant feeding choices. It also asked about early feeding practices (including herbal intake by the infant), sources of information, sources of support, and any feeding-related treatment for jaundice.

The Postnatal Questionnaires consist of various combinations of eight modules that were mailed to the mother approximately monthly from the time her infant was 2 months through 7 months of age, then three times (about every 7 weeks) until 12 months of age. Many of the modules included questions that were asked in some months but not others. View the timetable [PDF-43k] for the administration of each topic.

Module A: Infant Feeding and Health

Module A was sent with each Postnatal Questionnaire. This module contained one of the major measures of the study, the infant's food frequency checklist. It also asked about dietary supplement and herbal intake by infants, details about breastfeeding and infant formula feeding, infant health and use of medicines, infant weight and length, stool characteristics, and feeding of commercial baby foods. In month 2 only, it included a measure of postpartum depression.

The food frequency checklist in Module A enabled analysts to examine these types of questions:

  • Infant's age when introduced to solid food and the age when introduced to specific food groups
  • The infant's feeding schedule
  • Feeding of allergenic foods
  • Once supplemental foods are were introduced, the frequency of feeding each food group at each month of infancy
  • Any changes in eating patterns from month to month
  • The number of feedings per day of infant formula and breast milk

In addition, the checklist enabled researchers to analyze patterns of breastfeeding exclusivity, in particular whether mothers occasionally gave formula to an infant who was otherwise exclusively breastfed. Patterns of feeding foods other than breast milk and formula indicated the extent to which mothers followed current infant feeding guidelines, such as those published by national professional organizations. Information on whether foods fed to infants are baby foods or not provided information about exposure of infants to foods marketed for older children and adults, including foods fortified at levels only appropriate for older age groups.

Module B: Breastfeeding Cessation

Questions regarding breastfeeding cessation were included on each Postnatal Questionnaire, but they were answered only once, just after the mother had completely stopped breastfeeding. This module established the infant age when breastfeeding ceased and asked reasons for breastfeeding cessation and attitudes toward breastfeeding.

Module E: Infant Formula

Module E asked for details about formula feeding, formula label use and understanding, sources of information, brand formula choice, brand formula changing, and food safety practices. It asked for type of formula fed to the infant but not specific formula brand. Understanding current practices will contribute to more relevant and targeted consumer Education Information about a mother's use of infant formula labels and her evaluation of labels indicated how well the different parts of the label communicate to mothers. Module E was sent four times, at months 2, 5, 7, and 9.

Module H: Sleeping Arrangements, Child Care, Employment, and Health

Module H asked about all topics other than feeding. These included sleeping arrangements and position; child care and child care support for breastfeeding; details of the mother's employment and employer support for breastfeeding; how mothers managed to combine breastfeeding and work for pay; and the mother's overall health, weight status, and tobacco use. Module H was sent in months 3, 6, 9, and 12. A question about exposure to sunlight was administered at infant age 9 months.

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