Objectives: To estimate the interhospital differences in induction of labor (IOL) from 34(0/7) to 38(6/7) weeks' gestation by race/ethnicity.
Methods: Women between 34 and 42 weeks' gestation during 1995 and 2009 in three states were identified using linked maternal and infant records. Women with prior cesarean delivery, premature rupture of membranes, gestational hypertension, who delivered at hospitals with < 100 annual births, or who had missing data were excluded. The outcomes were inductions at early-term (ETI: between 37(0/7) and 38(6/7) weeks') and late preterm (LPI: from 34(0/7)-36(6/7) weeks') gestations. Cox proportional hazard ratios (HR) were used to estimate the independent associations between race/ethnicity and hospital of delivery on ETI and LPI.
Results: A total of 6.98 million eligible women delivered at 469 hospitals. ETI and LPI occurred in 3.20 and 0.40% of women, respectively. Non-Hispanic white women (3.99%) received ETI most commonly; conversely, LPI was highest among non-Hispanic black women (0.50%). In multivariable analyses, non-Hispanic black race was protective for ETI (HR = 0.89; p < 0.01) and was a risk factor for LPI (HR = 1.26; p < 0.01) after adjusting for patient factors and the delivery hospital.
Conclusion: Racial differences in ETI and LPI appear to be pervasive. Much of the unaccounted racial/ethnic variation remains seems secondary to within-hospital differences in selecting women for IOL.
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