The National Children's Study (NCS): establishment and protection of the inferential base

Comparison of Recruitment Strategy Outcomes in the National Children's Study

BACKGROUND AND OBJECTIVES

In 2000, the US Congress authorized the National Institutes of Health to conduct a prospective national longitudinal study of environmental influences on children's health and development from birth through 21 years. Several recruitment methodologies were piloted to determine the optimal strategy for a main National Children's Study.

METHODS

After an initial pilot recruitment that used a household enumeration strategy performed poorly, the National Children's Study Vanguard Study developed and evaluated the feasibility, acceptability, and cost of 4 alternate strategies to recruit a large prospective national probability sample of pregnant women and their newborn children. We compare household-based recruitment, provider-based recruitment, direct outreach, and provider-based sampling (PBS) strategies with respect to overall recruitment success, efficiency, cost, and fulfillment of scientific requirements.

RESULTS

Although all 5 strategies achieved similar enrollment rates (63%-81%) among eligible women, PBS achieved the highest recruitment success as measured by the ratio of observed-to-expected newborn enrollees per year of 0.99, exceeding those of the other strategies (range: 0.35-0.48). Because PBS could reach the enrollment target through sampling of high volume obstetric provider offices and birth hospitals, it achieved the lowest ratio of women screened to women enrolled and was also the least costly strategy. With the exception of direct outreach, all strategies enrolled a cohort of women whose demographics were similar to county natality data.

CONCLUSIONS

PBS demonstrated the optimal combination of recruitment success, efficiency, cost, and population representativeness and serves as a model for the assembly of future prospective probability-based birth cohorts.

The National Children's Study: an opportunity for medical toxicology

The National Children's Study (NCS) is a national longitudinal study that will prospectively investigate the influence of biological, environmental, genetic, and social factors on the health and development of US children. The NCS was mandated by the Children's Health Act of 2000 (Public Law 106-310) and is being implemented by the National Institutes of Health with input from the Centers for Disease Control and Prevention (CDC), the Environmental Protection Agency, and other federal departments and agencies. The NCS is a data-driven, evidence-based, community- and participant-informed study. Given its scale and scope, the NCS is an integrated system using several data acquisition strategies intended to provide evidenced-based design of methodologies and protocols. These strategies include the Vanguard Study, the Main Study, and formative research and sub-studies. The Vanguard Study, a pilot study, is currently underway and has been expanded from 7 to 37 study locations. The original study protocols and recruitment strategy have been field tested and revisions are under consideration. The CDC is collaborating with NCS in a pilot study that evaluates biological specimen protocols and will provide results on a broad array of environmental chemical exposures and nutritional indicators for a sample of Vanguard Study participants. This study is an example of the kind of collaborative opportunity that would benefit the NCS. Medical toxicologists have unique training in basic and clinical toxicology and laboratory assessments, and by partnering with study centers, both the NCS design and future NCS research projects could be enhanced.