Measuring Dosage: A Key Factor When Assessing the Relationship Between Prenatal Case Management and Birth Outcomes
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To assess whether a measure of prenatal case management (PCM) dosage is more sensitive than a dichotomous PCM exposure measure when evaluating the effect of PCM on low birthweight (LBW) and preterm birth (PTB). We constructed a retrospective cohort study (N = 16,657) of Iowa Medicaid-insured women who had a singleton live birth from October 2005 to December 2006; 28 % of women received PCM. A PCM dosage measure was created to capture duration of enrollment, total time with a case manager, and intervention breadth. Propensity score (PS)-adjusted odds ratios (ORs), and 95 % confidence intervals (95 % CIs) were calculated to assess the risk of each outcome by PCM dosage and the dichotomous PCM exposure measure. PS-adjusted ORs of PTB were 0.88 (95 % CI 0.70–1.11), 0.58 (95 % CI 0.47–0.72), and 1.43 (95 % CI 1.23–1.67) for high, medium, and low PCM dosage, respectively. For LBW, the PS-adjusted ORs were 0.76 (95 % CI 0.57–1.00), 0.64 (95 % CI 0.50–0.82), and 1.36 (95 % CI 1.14–1.63), for high, medium, and low PCM dosage, respectively. The PCM dichotomous participation measure was not significantly associated with LBW (OR = 0.95, 95 % CI 0.82–1.09) or PTB (0.97, 95 % CI 0.87–1.10). The reference group in each analysis is No PCM. PCM was associated with a reduced risk of adverse pregnancy outcomes for Medicaid-insured women in Iowa. PCM dosage appeared to be a more sensitive measure than the dichotomous measure of PCM participation.
KeywordsPrenatal case management Prenatal home visiting Birth outcomes Dose–response relationships
Special thanks to the Iowa Department of Public Health for making the data used in this study available for my dissertation. Additional thanks to Arden Handler, Leslie Stayner, Deborah Rosenberg, Deborah Kane and Kristin Rankin for feedback on earlier versions. This research was funded, in part, by the Illinois Public Health Research Pre-doctoral Fellowship, the MCHB funded Maternal and Child Health Epidemiology Program, and the Training Program in Perinatal Epidemiology Grant (T32 HD046377).
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