Background: CenteringPregnancy group prenatal care (GPNC) has been shown to reduce rates of preterm birth (PTB). We evaluated the impact of GPNC on spontaneous PTB (sPTB) as a first step in exploring the possible mechanism by which GPNC may decrease rates of PTB. We also evaluated whether attending more than five GPNC sessions affected PTB risk and examined all differences by race/ethnicity. Materials and Methods: We conducted a retrospective cohort study among women delivering at a single institution between April 2009 and March 2014. Birth outcome data from vital statistics records were appended to patient records, and detailed chart abstraction was used to determine spontaneous versus indicated PTB. The association between GPNC and attending more than five GPNC sessions and birth outcomes (i.e., PTB, sPTB, low birth weight [LBW], and neonatal intensive care unit [NICU] admissions) was analyzed using generalized estimating equation log binomial regression models. We examined effect modification of the associations by race/ethnicity. Results: The analysis included 1,292 women in GPNC and 8,703 in traditional individual prenatal care (IPNC). After controlling for potential confounders, the risk of PTB (risk ratio [RR] 0.38; 95% confidence interval [CI] 0.31-0.47), sPTB (RR 0.49; 95% CI 0.38-0.63), LBW (RR 0.46; 95% CI 0.37-0.56), and NICU admissions (RR 0.46; 95% CI 0.37-0.57) was lower in GPNC compared to IPNC women. Results differed by maternal race/ethnicity, with the strongest associations among non-Hispanic white mothers and the weakest associations among Hispanic mothers, especially for sPTB. Similarly, the risk of PTB, LBW, and NICU admissions was lower among GPNC women who attended more than five sessions. Conclusion: Participation in GPNC demonstrated a decreased risk for sPTB, as well as other adverse birth outcomes. In addition, participation in more than five GPNC sessions demonstrated a decreased risk for adverse birth outcomes. Prospective longitudinal studies are needed to further explore mechanisms associated with these findings.

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