Table 2

Population characteristics by study area

Maternal and pregnancy factorsAlberta Canada N=256 137%NSW Australia N=732 288%WA Australia N=149 624%Denmark N=645 993%Norway N=456 353%Scotland N=531 622%Sweden N=913 779%Massachusetts USA N=762 723%
Study period2002–20071998–20062000–20051997–20061999–20061997–20061997–20061998–2007
Maternal age (years)
Multiple births1.*2.3
Diabetes (any)
 Gestational diabetes3.
 Pre-existing DM0.
Chronic hypertension0.*
SmokingNA17.4*19.3*20.6* §18.6* 24.8*10.7* ††12.3
13.1* **
Induction of labour21.4*24.629.212.412.025.817.820.1
Mode of delivery
 Normal vaginal61.4*64.8*57.675.7*77.365.3*76.8*66.5
 Caesarean section25.624.730.017.114.822.215.727.4
Term births
 ≥40 weeks40.149.6*43.6*54.1*53.6*54.4*53.5*
 37–39 weeks51.243.948.839.440.038.640.8
Preterm births (all)
 Elective—see below2.§§1.6NA
Any pregnancy hypertension6.0*8.8*9.1**3.9*7.0
 Pre-eclampsia ≤34 weeks0.7‡‡
  • Percentages may not total 100 because of missing data.

  • * Decreasing over the study period, χ2 for trend p<0.01.

  • Increasing over the study period, χ2 for trend p<0.01.

  • Alberta—multiple birth data available for 98.5% of women.

  • § Denmark—smoking data available for 96% of women.

  • Norway—daily smoking in the first trimester (available for 83% of women).

  • ** Norway—daily smoking in the last trimester (available for 78% of women).

  • †† Sweden—smoking data available for 93% of women.

  • ‡‡ Alberta—gestational age available for 2004–2007.

  • §§ Scotland—elective caesarean sections only.