Table 1.
Characteristics of all singleton births, Sydney, 1998 to 2000
| Preterm (<37 weeks) n = 6 011 | Term (3742 weeks) n = 117 829 | OR+ (95% CI) | |
| Maternal age (years) Mean ± SD | 30.3 ± 5.8 | 30.2 ± 5.2 | 1.02 |
| Range | 15.0–50.1 | 12.1–53.3 | (1.02–1.03) |
| Maternal smoking during pregnancy Number (%) | |||
| Yes | 1 103 (18.4) | 14 475 (12.3) | 1.62 (1.51–1.74) |
| No | 4 905 (81.6) | 103 332 (87.7) | |
| Sex of infant Number (%) | |||
| Male | 3 369 (56.1) | 60 415 (51.3) | 1.22 (1.16–1.29) |
| Female | 2 634 (43.9) | 57 367 (48.7) | |
| Mother is Aboriginal or Torres Strait Islander Number (%) | |||
| Yes | 71 (1.2) | 746 (0.6) | 1.60 (1.24–2.07) |
| No | 5 934 (98.8) | 116 985 (99.4) | |
| Gestational age at first antenatal visit Number (%) | |||
| >20 weeks | 728 (12.5) | 13473 (11.5) | 1.05 (0.98–1.14) |
| ≤20 weeks | 5110 (87.5) | 103 642 (88.5) | |
| Previous pregnancy Number (%) | |||
| No | 2897 (48.2) | 50 060 (42.5) | 1.38 (1.30–1.45) |
| Yes | 3111 (51.8) | 67 737 (57.5) | |
| IRSD Quintile Number (%) | |||
| 5* (Least disadvantaged) | 1928 (32.1) | 42 632 (36.2) | 1.00 |
| 4 | 1363 (22.7) | 25 761 (21.9) | 1.18 (1.09–1.27) |
| 3 | 1009 (16.8) | 18 817 (16.0) | 1.18 (1.09–1.28) |
| 2 | 727 (12.1) | 13 090 (11.1) | 1.26 (1.15–1.38) |
| 1 (Most disadvantaged) | 984 (16.4) | 17 529 (14.9) | 1.27 (1.17–1.38) |
| Season of conception Number (%) | |||
| Summer* | 1540 (25.6) | 28 764 (24.4) | 1.00 |
| Autumn | 1513 (25.2) | 29 453 (25.0) | 0.97 (0.89–1.07) |
| Winter | 1540 (25.6) | 29 511 (25.1) | 0.92 (0.79–1.07) |
| Spring | 1418 (23.6) | 30 101 (25.6) | 0.86 (0.77–0.96) |
*Referent group; +Adjusted for all other covariates in Table 1