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Table 2 Percentage of all preterm births (20- < 37 weeks gestation) and third trimester preterm births (28- < 37 weeks gestation) by maternal smoking status, singleton births United States, 2010

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

Maternal Smoking Status N (%) Preterm (%) 20- < 37 weeks Preterm (%) 28- < 37 weeks
No trimester smokers 2,253,887 (90.67) (7.68) (7.23)
1st trimester only, low 28,560 (1.15) (8.90) (8.14)
1st trimester only, high 4909 (0.20) (8.68) (7.87)
1st & 2nd trimesters, low 11,619 (0.47) (12.99) (10.58)
1st & 2nd trimesters, high 2835 (0.11) (15.38) (12.57)
2nd & 3rd trimesters, low 5759 (0.23) (8.73) (8.34)
2nd& 3rd trimesters, high 584 (0.02) (9.42) (8.79)
All 3 trimesters, low 130,060 (5.23) (10.56) (10.09)
All 3 trimesters, high 47,530 (1.91) (11.35) (10.99)
  1. Low intensity: 1–19 cigarettes/day; high intensity: ≥ 20 cigarettes/day