Gestational age category | ||||
---|---|---|---|---|
Year | All preterm (n=51 711) OR* | 20–27 weeks (n=2697) OR** | 28–33 weeks (n=12 703) OR* | 34–36 weeks (n=36 311) OR* |
Multivariate analysis adjusted for gender, maternal age, parity, birth year, decile and birth year*decile, year*age, year*parity, decile*age, decile*parity. | ||||
*Odds ratios (OR) for preterm birth amongst decile 10 women compared to those in decile 1 for each particular year reflects the social gradient for that year. | ||||
**Odds ratios for the 20–27 week category did not reach statistical significance. | ||||
1980 | 1.36 | 1.18 | 1.39 | 1.36 |
1990 | 1.26 | 1.27 | 1.25 | 1.26 |
1999 | 1.17 | 1.35 | 1.14 | 1.17 |