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. 2009 May 12;6(5):e1000061. doi: 10.1371/journal.pmed.1000061

Figure 4. Stratified analysis of association between preconceptional folate supplementation ≥1 y and the risk of spontaneous preterm birth before 32 wk.

Figure 4

ORs and 95% CIs of spontaneous preterm birth before 32 wk for preconceptional folate supplementation for ≥1 y, stratified for a given characteristic and adjusted for all other maternal characteristics. p-Values are estimated for interaction terms between duration of folate supplementation and given characteristic. The OR for BMI <18.5 could not be estimated, as there were no cases of spontaneous preterm birth before 32 wk among women using folate supplementation for ≥1 y and with BMI <18.5. MA, maternal age; Educ, completed years of education; PARA No PPTB, parous woman without a history of prior preterm birth; PARA PPTB, parous woman with a history of prior preterm birth.