Relative and absolute differences in preterm and very preterm births among non-Hispanic black women relative to non-Hispanic white women in Canada and the United States, 2004–2006
| Measure; outcome | Crude | Adjusted* | Adjusted† | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Canada | US | pH value‡ | Canada | US§ | pH value‡ | Canada | US§ | pH value‡ | |
| Risk ratio (95% CI) | |||||||||
| Preterm birth (< 37 v. 37–41 wk) | 1.49 (1.32 to 1.66) | 1.57 (1.56 to 1.58) | 0.3 | 1.46 (1.29 to 1.63) | 1.41 (1.40 to 1.42) | 0.5 | 1.60 (1.39 to 1.81) | 1.45 (1.44 to 1.47) | 0.1 |
| Very preterm birth (< 32 v. 32–41 wk) | 2.70 (1.95 to 3.44) | 2.81 (2.77 to 2.86) | 0.8 | 2.61 (1.88 to 3.35) | 2.36 (2.31 to 2.40) | 0.5 | 2.62 (1.83 to 3.41) | 2.43 (2.36 to 2.52) | 0.6 |
| Risk difference (95% CI) | |||||||||
| Preterm birth (< 37 v. 37–41 wk) | 2.94 (1.91 to 3.96) | 4.63 (4.56 to 4.70) | 0.003 | 2.76 (1.74 to 3.78) | 3.41 (3.33 to 3.48) | 0.2 | 3.59 (2.32 to 4.85) | 3.57 (3.43 to 3.70) | 1.0 |
| Very preterm birth (< 32 v. 32–41 wk) | 1.22 (0.71 to 1.73) | 1.67 (1.64 to 1.70) | 0.08 | 1.16 (0.66 to 1.67) | 1.31 (1.28 to 1.35) | 0.6 | 1.17 (0.62 to 1.71) | 1.32 (1.25 to 1.38) | 0.6 |
Note: CI = confidence interval.
* Term birth = 37–41 wk, preterm = < 37 wk, very preterm = < 32 wk.
↵* Adjusted for maternal age, maternal education, marital status, birth order, sex of child and missing paternal information.
↵† Adjusted for maternal age, maternal education, marital status, birth order, sex of child, missing paternal information and maternal nativity. For the US sample, the estimates include only births in 2004 (n = 1 493 259).
↵‡ pH = p value for χ2 test for heterogeneity of the risk ratios or risk differences.
↵§ Adjusted US estimates are standardized to the covariate distribution of the Canadian study population.