Transitions in pregnancy planning in women recruited for a large prospective cohort study.

STUDY QUESTION: Do the rates at which women transition among different intensities of pregnancy planning vary with age, marital status and race/ethnicity?

SUMMARY ANSWER: Rates of transition from low or moderate pregnancy probability groups (PPGs) to higher PPGs vary by age, marital status and race/ethnicity.

WHAT IS KNOWN ALREADY: The design of prospective studies of the effects of pre- and peri-conception exposures on fecundity, pregnancy and children's health is challenging because at any specific time only a small percentage of reproductive age women is attempting to conceive. To our knowledge, there has been no population-based, prospective study that repeatedly assessed pregnancy planning, which included women who were not already planning pregnancy at enrollment and whose ages spanned the female reproductive age range.

STUDY DESIGN, SIZE, DURATION: A longitudinal study was carried out that repeatedly assessed pregnancy probability in 12 916 women for up to 21 months from January 2009 to September 2010.

PARTICIPANTS/MATERIALS, SETTING, METHOD: We analyzed data from the National Children's Study Vanguard Study, a pilot study for a large-scale epidemiological birth cohort study of children and their parents. During the Vanguard Study, investigators followed population-based samples of reproductive age women in each of seven geographically dispersed and diverse study locations over time to identify when they sought to become pregnant, providing a unique opportunity to prospectively assess changes in pregnancy planning in a large sample of US women. At study entry and each follow-up contact, which occurred at 1, 3 or 6 month intervals depending on PPG, a questionnaire was used to assess behavior dimensions of pregnancy planning to assign women to low, moderate, high non-tryer and high tryer PPGs.

MAIN RESULTS AND THE ROLE OF CHANCE: Crude rates of pregnancy increased with higher assigned PPG, validating the utility of the instrument. The initial PPG and probabilities of transitioning from low or moderate PPG to higher PPG or pregnancy varied with age, marital status and race/ethnicity. Women aged 25 to <35 years had shorter times to transition to higher PPGs or to pregnant compared with women <25 years. Women who were not currently married had longer times to transition from any initial PPG to pregnant, high tryer or high non-tryer status than currently married women. Non-Hispanic Black (NHB) and Hispanic women had shorter time to transition from low or moderate to high non-tryer than non-Hispanic White (NHW) women. NHB women also had shorter time to transition from low to high tryer than NHW women. High tryers are more likely to be aged 25 to <30 years, to be married, and to be Hispanic, NHB or other race/ethnicity than women in the low PPG.

LIMITATIONS, REASONS FOR CAUTION: Loss to follow-up varied by age, marital status and race/ethnicity. Although weights were not developed for the Vanguard study, the self-weighting design minimizes the bias of unweighted analysis. Nonetheless, the SEs for some estimates may be under-estimated.

WIDER IMPLICATIONS OF THE FINDINGS: Our results show that demographic characteristics are strong predictors of women's behaviors toward pregnancy. The results further show that frequent follow-up assessments of pregnancy planning behavior in large numbers of women are required to recruit an unbiased sample of preconception women. These findings will be useful to investigators designing prospective studies of fecundability, pregnancy outcomes and children's health.

STUDY FUNDING/COMPETING INTERESTS: National Institutes of Health (contracts N01-HD53414, N01-HD63416, N01-HD53410, N01-HD53415, N01-HD53396, N01-HD53413 and N01-HD-53411; grant R21 ES016846) and by the University of California Irvine Center for Occupational and Environmental Health. No competing interests.

TRIAL REGISTRATION NUMBER: None.