Distribution of the risk factors in each group.
| Variables | <32 weeks(n=1703) | 32–33 weeks(n=2345) | 34–36 weeks(n=11785) | 37–41 weeks(199421) | P-value* |
|---|---|---|---|---|---|
| Maternal age (years) | #x00A0; | #x00A0; | #x00A0; | #x00A0; | <0.001 |
| <20 | 83 (4.9) | 123 (5.2) | 403 (3.4) | 4584 (2.3) | #x00A0; |
| 20–34 | 1345 (79.0) | 1915 (81.7) | 9864 (83.7) | 177395 (89.0) | #x00A0; |
| ≥35 | 275 (16.1) | 307 (13.1) | 1518 (12.9) | 17442 (8.7) | #x00A0; |
| Parity ≥ 2 | 704 (41.3) | 905 (38.6) | 4275 (36.3) | 59419 (29.8) | <0.001 |
| HDP | 119 (7.0) | 182 (7.8) | 706 (6.0) | 3486 (1.7) | <0.001 |
| GDM | 76 (4.5) | 100 (4.3) | 547 (4.6) | 7020 (3.5) | <0.001 |
| ICP | 12 (0.7) | 38 (1.6) | 297 (2.5) | 1973 (0.5) | <0.001 |
| Anemia | 37 (2.2) | 61 (2.6) | 190 (1.6) | 2407 (1.2) | <0.001 |
| Chorioamnionitis | 48 (2.8) | 35 (1.5) | 113 (1.0) | 787 (0.4) | <0.001 |
| Placenta previa | 47 (2.8) | 46 (2.0) | 191 (1.6) | 6392 (0.2) | <0.001 |
| Placental abruption | 24 (1.4) | 26 (1.1) | 46 (0.4) | 66 (0.0) | <0.001 |
| Fetal distress | 124 (7.3) | 166 (7.1) | 542 (4.6) | 80718 (4.0) | <0.001 |
Values are presented as number and percentages (%).
↵* P-value indicates results of χ2 test comparing proportions of the distribution of risk factors for preterm subgroups. HDP: hypertension disorders in pregnancy, ICP: intrahepatic cholestasis of pregnancy, GDM: gestational diabetes mellitus