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Table 1 Distributions of selected characteristics between PB and term births

From: Effects of Benzo[a]pyrene-DNA adducts, dietary vitamins, folate, and carotene intakes on preterm birth: a nested case–control study from the birth cohort in China

Characteristics Term births (N = 82) PBs (N = 83) Pa
N % N %
Maternal age (years)
  < 30 52 63.4 54 65.1 0.83
  ≥ 30 30 36.6 29 34.9
Highest education level
  < College 29 35.4 42 50.6 0.048
  ≥ College 53 64.6 41 49.4
Family monthly income (RMB per capita)
  < 3,000 33 4.02 46 55.4 0.051
  ≥ 3,000 49 59.8 37 44.6
Employment during pregnancy
 No 48 58.5 53 63.9 0.48
Yes 34 41.5 30 36.1
Pre-pregnancy BMIb
  ≤ 18.5 16 19.5 13 15.7 0.68
 18.5–24.0 52 63.4 58 69.9
  ≥ 24.0 14 17.1 12 14.5
Parity
 Primiparous 57 69.5 51 61.5 0.28
 Multiparous 25 30.5 32 38.6
C-section
 No 51 62.2 41 49.4 0.098
 Yes 31 37.8 42 50.6
Gender
 Female 37 45.1 39 47.0 0.81
 Male 45 54.9 44 53.0
Passive smoking during pregnancy
 No 69 84.2 76 91.6 0.14
 Yes 13 15.9 7 8.4
Activities during pregnancy
 No 10 12.2 21 25.3 0.031
 Yes 72 87.8 62 74.7
Supplement intake
 Never 15 18.3 17 20.5 0.72
 Ever 67 81.7 66 79.5
  1. aCalculated by Chi-square analysis
  2. bWeight (kg) / height (m)2
  3. Abbreviations: BMI Body mass index, PB Preterm birth