The LIFE Study used a prospective cohort design suitable for following couples across sensitive windows of human reproduction and development. Specifically, couples interested in becoming pregnant in the next 2 months were recruited and followed until pregnant or up to 12 months of attempting pregnancy between 2005 and 2009. In addition, pregnant women were followed to delivery or through a pregnancy loss. The target population comprised individuals residing in four Michigan counties with reported exposure to persistent organochlorine chemicals (i.e. Berrien, Calhoun, Ingham, Kalamazoo) and 12 counties in Texas (i.e. Aransas, Brazoria, Calhoun, Chambers, Fort Bend, Galveston, Harris, Jefferson, Matagorda, Montgomery, Nueces and Orange) with presumed exposure to persistent environmental chemicals. By design, the targeted population comprising potentially exposed individuals and their partners was intended to be inclusive of couples irrespective of gynaecological and/or urological history who were interested in becoming pregnant apart from sterilised couples or those who were told by a physician that they could not achieve pregnancy without medical assistance. The inclusion criteria were: (a) married or in a committed relationship; (b) females aged 18–40 and males aged 18+ years; (c) able to communicate in English or Spanish; (d) self-reported menstrual cycles ranging from 21 to 42 days consistent with the fertility monitor's requirement; and (e) no hormonal birth control injections in the past 12 months, given the uncertain return of ovulation. Our a priori sample size was 500 couples powered to be able to detect a reduction in fecundity in relation to differences in environmentally relevant concentration of organochlorine chemicals. We used data from the New York State Angler Cohort Study for the range of power assumptions, as it is the only prospective time-to-pregnancy study that had individual serum organochlorine concentrations for participating women.12 (link)A different sampling framework was utilised in each geographical location to recruit individuals, given the absence of a uniformly available approach in each state for identifying and recruiting reproductive aged couples planning pregnancies. This provided a unique opportunity to assess the efficacy of sampling frameworks on recruitment. Specifically, the Texas site used the Texas Parks and Wildlife Department's angler database for recruitment, while the Michigan site used a commercially available marketing database – InfoUSA® – that utilised recruitment filters to identify individuals with fishing interests (e.g. fishing magazine subscriptions). The former sampling framework comprises all commercial and recreational fishing licences in Texas, and was stratified by licence type and census track to achieve diversity. As race and ethnicity are not reported in this registry, the North American Association of Central Cancer Registries Hispanic Identification Algorithm was used to help oversample on presumed Hispanic ethnicity. The InfoUSA® sampling framework was assessed in two Michigan counties and found to provide complete coverage of households based upon data from the 2000 Census assuming some level of migration. Additional efforts were undertaken to oversample under-represented minorities and individuals living in census tracts with low median household incomes (≥$40 000). Prior to mailing letters, contact information was updated with commercially available software (e.g. Telematch and Metronet).
Recruitment began with an introductory letter and study brochure mailed to targeted individuals followed by a telephone call within 2 weeks, at which time contacted individuals were screened for eligibility. Up to 10 follow-up telephone calls were placed at varying times and days to reach targeted individuals by two call centres (http://ppri.tamu.edu; http://www.rti.org) consistent with their established survey methods. Each partner of the couple was individually screened for enrolment even if that meant additional telephone calls. The contact information of eligible and preliminarily consenting couples was given to the research coordinators at each site, who then assigned interviewers to couples. In-home interviews and training sessions were scheduled at the couple's convenience. The LIFE Study was conducted between 2005 and 2009.