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. Author manuscript; available in PMC: 2016 Apr 21.
Published in final edited form as: Am J Obstet Gynecol. 2015 Aug 12;213(6):844.e1–844.e6. doi: 10.1016/j.ajog.2015.08.014

FIGURE 2. RR of PTB for women randomized to 17OHP-C vs placebo.

FIGURE 2

Relative risk (RR) of preterm birth (PTB) (<37 weeks) for progesterone vs placebo. Unadjusted RR (open circles) and adjusted RR (closed circles) from binomial regression. Each adjusted model is result of backward selection process that considered: race (black vs otherwise), smoking cigarettes during pregnancy, marital status, maternal age >30 years, years of education, and illicit drug or alcohol use during pregnancy, as well as interactions between smoking and weight/body mass index (BMI), and smoking and treatment as potential covariates. For each adjusted binomial model, >1 previous PTB was only predictor to remain as covariate. Integer weight at which confidence intervals (CI) begin to include RR = 1 was 166 lb in unadjusted model, and 164 lb in model including previous PTB.