Table 2 OR for preterm birth by level of education (reference: high education) after adjustment for each covariate separately and the corresponding change (%) in OR relative to the basic model
OR for preterm birth by level of education
High (n = 1264)Mid–high (n = 955)Mid–low (n = 973)Low (n = 638)
Model 1 (basic model, BM)*Reference0.89 (0.59 to 1.36)0.82 (0.54 to 1.26)1.89 (1.28 to 2.80)
Pregnancy characteristics
    BM + pregnant women’s ageReference0.87 (0.57 to 1.33)0.77 (0.50 to 1.19)1.69 (1.10 to 2.60)
    BM + pregnant women’s heightReference0.89 (0.58 to 1.35)0.79 (0.52 to 1.21)1.69 (1.13 to 2.51)
    BM + preeclampsiaReference0.90 (0.59 to 1.37)0.79 (0.51 to 1.20)1.77 (1.19 to 2.63)
    BM + IUGRReference0.88 (0.58 to 1.34)0.78 (0.51 to 1.20)1.78 (1.19 to 2.65)
Psychosocial factors
    BM + marital statusReference0.89 (0.59 to 1.36)0.83 (0.54 to 1.26)1.91 (1.28 to 2.86)
    BM + pregnancy planningReference0.89 (0.59 to 1.36)0.82 (0.54 to 1.26)1.89 (1.26 to 2.84)
    BM + financial concernsReference0.88 (0.58 to 1.33)0.79 (0.52 to 1.22)1.72 (1.13 to 2.60)
    BM + long-lasting difficultiesReference0.88 (0.58 to 1.34)0.80 (0.52 to 1.23)1.79 (1.19 to 2.69)
    BM + psychopathologyReference0.88 (0.58 to 1.33)0.79 (0.51 to 1.21)1.75 (1.16 to 2.62)
    BM + working hoursReference0.89 (0.58 to 1.37)0.82 (0.53 to 1.28)1.89 (1.21 to 2.98)
Lifestyle habits
    BM + smoking habitsReference0.89 (0.58 to 1.35)0.81 (0.53 to 1.25)1.82 (1.19 to 2.78)
    BM + alcohol consumptionReference0.86 (0.57 to 1.32)0.80 (0.51 to 1.23)1.74 (1.15 to 2.64)
    BM + BMIReference0.89 (0.59 to 1.35)0.81 (0.53 to 1.24)1.83 (1.23 to 2.73)
  • Values are ORs (95% CI): risk for preterm birth compared to the reference group (high education), and corresponding change (%) in OR relative to the basic model and due to the covariate.

  • *BM: adjusted for parity of the pregnant woman and gender of the child.

  • BM, basic model; BMI, body mass index; IUGR, intrauterine growth restriction.