Skip to main content

Table 3 The odds of all preterm births (20- < 37 weeks gestation) and third trimester preterm births (28- < 37 weeks gestation) across maternal smoking status categories

From: A gestational vulnerability window for smoking exposure and the increased risk of preterm birth: how timing and intensity of maternal smoking matter

Preterm 20- < 37 weeks
Smoking Status Crude OR 95% CI Adjusted ORa 95% CI
 No trimester smokers 0.85 0.82, 0.89* 0.90 0.86, 0.94*
 1st trimester only, low (ref.) 1 1 1 1
 1st trimester only, high 0.97 0.87, 1.08 0.98 0.88, 1.09
 1st & 2nd trimesters, low 1.53 1.43, 1.64* 1.51 1.41, 1.61*
 1st & 2nd trimesters, high 1.86 1.67, 2.07* 1.85 1.66, 2.06*
 2nd & 3rd trimesters, low 0.98 0.89, 1.08 0.95 0.86, 1.05
 2nd & 3rd trimesters, high 1.06 0.80, 1.41 1.03 0.77, 1.36
 All 3 trimesters, low 1.21 1.16, 1.26* 1.20 1.14, 1.25*
 All 3 trimesters, high 1.31 1.25, 1.38* 1.33 1.26, 1.40*
Preterm 28- < 37 weeks
Smoking Status Crude OR 95% CI Adjusted ORa 95% CI
 No trimester smokers 0.88 0.84, 0.92* 0.93 0.89, 0.97*
 1st trimester only, low (ref.) 1 1 1 1
 1st trimester only, high 0.96 0.86, 1.08 0.97 0.86, 1.08
 1st & 2nd trimesters, low 1.34 1.24, 1.44* 1.32 1.22, 1.42*
 1st & 2nd trimesters, high 1.62 1.44, 1.83* 1.61 1.43, 1.82*
 2nd & 3rd trimesters, low 1.03 0.93, 1.14 1.00 0.90, 1.11
 2nd & 3rd trimesters, high 1.09 0.81, 1.46 1.05 0.79, 1.40
 All 3 trimesters, low 1.27 1.21, 1.33* 1.25 1.20, 1.31*
 All 3 trimesters, high 1.39 1.32, 1.47* 1.40 1.33, 1.48*
  1. aAnalyses were adjusted for: maternal race/ethnicity, age, education, and marital status; low intensity: 1–19 cigarettes/day; high intensity: ≥ 20 cigarettes/day; *p < 0.05; CI-confidence interval