The risk of preterm birth in different sociodemographic groups and the prevalence of these characteristics in the study periods 1990–1994, 1995–1999, 2000–2004, 2005–2009 and 2010–2014
| Characteristics | Calendar period | |||||||||
| 1990–1994 | 1995–1999 | 2000–2004 | 2005–2009 | 2010–2014 | ||||||
| n=13 085 | n=12 798 | n=13 371 | n=12 066 | n=11 743 | ||||||
| ORa (95% CI) | P | ORa (95% CI) | P | ORa (95% CI) | P | ORa (95% CI) | P | ORa (95% CI) | P | |
| Parity | ||||||||||
| <3 | 0.80 (0.73 to 0.87) | 69 | 0.71 (0.65 to 0.78) | 75 | 0.60 (0.54 to 0.67) | 80 | 0.57 (0.50 to 0.64) | 86 | 0.60 (0.49 to 0.71) | 91 |
| ≥3 | 1 | 31 | 1 | 25 | 1 | 20 | 1 | 14 | 1 | 9 |
| Education (years) | ||||||||||
| <6 | 1 | 72 | 1 | 58 | 1 | 41 | 1 | 37 | 1 | 24 |
| ≥6 | 0.79 (0.72 to 0.87) | 28 | 0.84 (0.77 to 0.92) | 42 | 0.73 (0.66 to 0.80) | 59 | 0.78 (0.69 to 0.87) | 63 | 0.84 (0.73 to 0.97) | 76 |
Adjusted for women’s age, parity, education in years and household wealth index
Prevalence is provided as per ccent
CI, confidence interval; ORa, odds ratio adjusted; P, prevalence.