TABLE 1

Disposition of the IFPS II Sample for the Prenatal Questionnaire, Birth Screener, and Neonatal Questionnaire

DispositionSubtotalTotal
Prenatal questionnaire
    Total mailed, n15147
    Disqualified from mailing list after questionnaires were mailed, n529
        Undeliverable, n484
        Duplicate, n5
        Gulf Coast hurricane zip code, na40
    Adjusted total mailed, n14618
    Disqualified, n601
        Infant already born, n21
        Miscarried, n18
        Under 18 y, n95
        Expecting twins, n92
        No one in household pregnant, n375
    Refused, n46
    Not returned, n9069
    Complete and qualified, nb4902
Birth screener
    Total prenatal respondents, n4902
    Disqualified from mailing list after questionnaires were mailed, n67
        Undeliverable, n19
        Gulf Coast hurricane zip code, na48
    Adjusted total attempted to reach, n4835
    Disqualified, nc673
        No one in household pregnant, n16
        Infant not due in date range, n193
        Infant died, n10
        Birth weight < 5 lb, n82
        Multiple births, n17
        Mother had medical problems that prevented her from feeding the infant for >1 wk, n89
        Infant stayed in intensive care >3 d, n107
        Infant had medical problems that affected feeding, n115
        Born prematurely (born ≥36 d before due date), n38
        Born after field closing date, n6
    Refused, n4
    No due date given, n46
    Returned after due date, n58
    No answer, n618
    Complete and qualified, n3452
    Response rate: (No. of surveys completed/adjusted No. of interviews attempted) − No. of women disqualified, %82.9
Neonatal questionnaire
    Total mailed, nd4226
    Disqualified from mailing list after questionnaires were mailed, n213
        Undeliverable, n31
        Duplicate, n12
        Gulf Coast hurricane zip code, na8
        Accidentally dropped from sample, n162
    Adjusted total mailed, n4013
    Disqualified, ne70
        Born prematurely (born ≥36 d before due date), n38
        Born after field date, n6
        Long-term illness, nf26
    Refused, n23
    Not returned, n890
    Complete and qualified, n3033
    Response rate: (No. of surveys completed/adjusted No. mailed − No. of women disqualified), %76.9
  • a Sample members were excluded from the remainder of the study if they resided in the zip codes to which the US Postal Service stopped delivery as a result of the 2005 Gulf Coast hurricanes.

  • b Response rates for the prenatal questionnaire could not be calculated because only eligible respondents returned the questionnaire. The likely number ineligible could not be estimated because women could be disqualified for multiple reasons and data showing how these criteria overlap are not available.

  • c When a respondent was disqualified on the birth screener for a specific reason, the remaining potential disqualifying conditions were not assessed. The conditions are listed in the order in which they were asked on the questionnaire, beginning with multiple births. Respondents were not asked whether their infant had died, but they were expected to give this information if their infant had died.

  • d Mothers who could not be reached for the birth screener by telephone or an interactive voice-response interview were mailed a neonatal questionnaire and birth screener at the same time. Therefore, some mothers who did not complete a birth screener were mailed a neonatal questionnaire.

  • e Because some respondents received the birth screener at the same time as the neonatal questionnaire, respondents were disqualified on the neonatal questionnaire for some of the birth-screener reasons. Cases in the first 2 reasons for disqualification are duplicates of disqualifications from the birth screener.

  • f Throughout the study, women were disqualified if they indicated that their infant had a long-term illness or condition, including Down syndrome, cleft palate, Duarte galactosemia, dysphagia, and pyloric spasms.