Table 2. Risk estimates for spontaneous preterm birth according to some maternal socio-demographic conditions, comparing women who delivered prematurely (CASES) and women who delivered at term (CONTROLS).
| Socio-demographic conditions | CASES | CONTROLS | OR* (95% CI) |
| n (%) | n (%) | ||
| Maternal age (years) | |||
| • ≤19 | 681 (25.4) | 211 (18.4) | 1.54 (1.31–1.79) |
| • 20–34 | 1700 (63.4) | 809 (70.6) | Ref. |
| • ≥35 | 301 (11.2) | 126 (11.0) | 1.14 (0.84–1.54) |
| Skin colour | |||
| • White | 1158 (43.2) | 451 (39.4) | Ref. |
| • Other | 1524 (56.8) | 695 (60.6) | 0.85 (0.65–1.12) |
| Marital status | |||
| • With a partner | 2020 (75.3) | 919 (80.2) | Ref. |
| • Without a partner | 662 (24.7) | 227 (19.8) | 1.33 (1.08–1.63) |
| Household | |||
| • Urban | 2399 (89.9) | 1021 (89.5) | Ref. |
| • Rural | 269 (10.1) | 120 (10.5) | 0.95 (0.67–1.35) |
| Schooling (years) | |||
| • ≤8 | 1095 (41.4) | 420 (37.2) | 1.15 (0.76–1.75) |
| • 9–12 | 1365 (51.6) | 629 (55.7) | 0.96 (0.65–1.42) |
| • >12 | 183 (6.9) | 81 (7.2) | Ref. |
| Family income | |||
| • ≥ US$ 400,00 | 910 (37.5) | 395 (36.4) | Ref. |
| • <US$ 400,00 | 1519 (62.5) | 690 (63.6) | 0.96 (0.81–1.13) |
| Paid work in pregnancy | |||
| • No | 1745 (65.4) | 690 (60.3) | Ref. |
| • Yes | 923 (34.6) | 455 (39.7) | 0.80 (0.65–0.99) |
| Paid work until | |||
| • First trimester | 68 (7.4) | 14 (3.1) | 2.98 (1.39–6.38) |
| • Second trimester | 230 (24.9) | 58 (12.7) | 2.43 (1.77–3.35) |
| • Third trimester | 624 (67.7) | 383 (84.2) | Ref. |
| Strenuous work | |||
| • No | 505 (55.0) | 257 (56.6) | Ref. |
| • Yes/sometimes | 414 (45.0) | 197 (43.4) | 1.07 (0.82–1.40) |
| Standing work | |||
| • No | 355 (38.8) | 171 (37.7) | Ref. |
| • Yes/sometimes | 561 (61.2) | 282 (62.3) | 0.96 (0.77–1.19) |
| Workload (daily) | |||
| • ≤8 hours | 629 (68.9) | 324 (71.7) | Ref. |
| • >8 hours | 284 (31.1) | 128 (28.3) | 1.14 (0.78–1.66) |
| Night work | |||
| • No | 724 (79.6) | 355 (78.7) | Ref. |
| • Yes | 185 (20.4) | 96 (21.3) | 0.94 (0.66–1.36) |
| Housework | |||
| • No | 166 (6.2) | 43 (3.8) | Ref. |
| • Yes/sometimes | 2515 (93.8) | 1102 (96.2) | 0.59 (0.39–0.90) |
| Children under 5 years | |||
| • No | 1901 (70.9) | 821 (71.7) | Ref. |
| • Yes | 780 (29.1) | 324 (28.3) | 1.04 (0.91–1.18) |
| Total | 2,682 (100) | 1,146 (100) |
OR*: Odds Ratio adjusted for the cluster effect design; CI: confidence interval.
Values in bold mean they are statistically significant.