Table 2

Multivariate logistic analysis of risk factors for preterm delivery in Denmark, 1995-2004

All pretermExtremely preterm*Very preterm*Moderately preterm*
NoOdds ratio (95% CI)NoOdds ratio (95% CI)NoOdds ratio (95% CI)NoOdds ratio (95% CI)
Mode of conception:
Spontaneous63 092834 0391.0013791.0036071.0029 0531.00
In vitro fertilisation15 2162 7111.25 (1.19 to 1.32)1971.76 (1.47 to 2.12)3451.15 (1.01 to 1.31)2 1691.17 (1.10 to 1.24)
Initiation of delivery:
Spontaneous55 726729 8701.0014331.0033441.0025 0931.00
Elective88 8776 8801.09 (1.06 to 1.12)1430.39 (0.33 to 0.46)6080.77 (0.71 to 0.85)6 1291.19 (1.15 to 1.23)
Parity:
Primiparous28 708019 9381.53 (1.49 to 1.57)9311.79 (1.60 to 1.99)22401.63 (1.52 to 1.74)16 7671.48 (1.44 to 1.51)
Multiparous35 906416 8121.006451.0017121.0014 4551.00
Type of pregnancy:
Singleton633 01230 8591.0012501.0031711.0026 4381.00
Multiple13 1325 89114.03 (13.75 to 14.90)32611.12 (9.6 to 12.87)78111.88 (10.83 to 13.02)4 78411.70 (11.22 to 12.20)
Maternal age646 14436 7501.01 (1.01 to 1.01)15761.03 (1.02 to 1.04)39521.02 (1.01 to 1.02)31 2221.01 (1.01 to 1.01)
Year646 14436 7501.03 (1.02 to 1.03)15761.06 (1.04 to 1.07)39521.03 (1.01 to 1.04)31 2221.02 (1.02 to 1.03)
Smoking:
Non-smoker489 12924 8201.009161.0024791.0021 4251.00
Smoker131 9149 1901.52 (1.49 to 1.55)3792.26 (2.11 to 2.42)10411.76 (1.68 to 1.85)7 7701.41 (1.38 to 1.44)
Ethnic origin:
White European608 33934 7780.93 (0.88 to 0.97)14930.86 (0.69 to 1.07)37510.94 (0.81 to 1.09)29 5340.94 (0.89 to 0.98)
Other37 7971 9721.00831.002011.001 6881.00
  • CI, confidence interval.

  • All odds ratios were mutually adjusted for other variables in the table.

  • * Extremely preterm: 22-27 completed weeks of gestation; very preterm: 28-31; moderately preterm: 32-36; term: ≥37.

  • † Odds ratio for a one year change in age.

  • ‡ Odds ratio for a one year change in calendar time.