Table 5 Population attributable fractions for maternal systemic/localized comorbidity and preterm birth according to clinical subtype and gestational age*
|  | Medically indicated | PPROM* | Spontaneous†| ||||||
|---|---|---|---|---|---|---|---|---|---|
| Â | < 28 wk | 28-31 wk | 32-36 wk | < 28 wk | 28-31 wk | 32-36 wk | < 28 wk | 28-31 wk | 32-36 wk |
Systemic comorbidity | Â | Â | Â | Â | Â | Â | Â | Â | Â |
   Hypertension |  |  |  |  |  |  |  |  |  |
Preeclampsia/eclampsia | 21.6 | 38.0 | 21.9 | -1.2 | -0.7 | -0.2 | -1.2 | -0.6 | 0.2 |
Pre-existing | 0.8 | 1.1 | 1.6 | 0 | 0.1 | 0.1 | 0 | 0 | -0.1 |
Gestational | 0.2 | 1.8 | 1.8 | -4.5 | -0.8 | -0.4 | -2.4 | -4.3 | -0.3 |
   Cardiovascular disease | 0.4 | 0.8 | 0.6 | 0.1 | 0.5 | 0.1 | 0.2 | 0.3 | 0.02 |
   Diabetes |  |  |  |  |  |  |  |  |  |
Pre-existing | 0.3 | 2.7 | 3.4 | 0.1 | 3.0 | 1.2 | -0.1 | 1.4 | 0.5 |
Gestational | -1.9 | 0.6 | 2.6 | -1.5 | 1.0 | 1.8 | -3.0 | -0.8 | 1.1 |
   Edema/renal disease | 1.6 | 2.9 | 1.7 | 0.1 | 0.2 | 0.02 | 0.2 | -0.03 | 0.03 |
   Genitourinary infection | 1.7 | 3.7 | 1.9 | 1.7 | 3.6 | 0.5 | 0.7 | -0.02 | -0.05 |
   General infection | 1.8 | 1.4 | 1.4 | 1.6 | 2.1 | 0.4 | 0.9 | 1.2 | 0.3 |
   Thyroid disease | 1.4 | 1.0 | 0.9 | 0.6 | 0.8 | 0.3 | 0.1 | 0.5 | 0.1 |
   Anemia | 11.9 | 14.8 | 5.9 | 6.7 | 6.6 | -1.1 | 3.3 | -0.1 | -2.9 |
   Drug dependence | 0.03 | 0.9 | 0.5 | 0.8 | 0.9 | 0.5 | 0.7 | 1.1 | 0.7 |
   Mental disorders | 1.7 | 0.9 | 0.8 | 0.9 | 1.8 | 0.5 | 1.0 | 0.8 | 0.4 |
Localized comorbidity | Â | Â | Â | Â | Â | Â | Â | Â | Â |
   Hemorrhage |  |  |  |  |  |  |  |  |  |
Placental abruption | 23.5 | 21.0 | 9.8 | 14.1 | 17.9 | 2.4 | 25.2 | 22.9 | 4.5 |
Placenta previa | 3.3 | 5.9 | 6.6 | 2.2 | 1.2 | 0.3 | 0.5 | 0.4 | -0.1 |
   Chorioamnionitis | 10.5 | 2.0 | -0.3 | 31.4 | 30.7 | 3.8 | 25.1 | 11.7 | 0.04 |
   Amniotic sac |  |  |  |  |  |  |  |  |  |
Polyhydramnios | 1.3 | 2.3 | 1.5 | 0.3 | 0.8 | 0.2 | 0.7 | 1.8 | 0.4 |
Oligohydramnios | 8.7 | 10.3 | 7.0 | 8.2 | 10.2 | 1.2 | 1.6 | 0.6 | -0.2 |
   Cervical incompetence | 7.2 | 1.4 | 0.7 | 8.1 | 3.5 | 0.5 | 14.6 | 3.1 | 0.6 |
   Structural abnormality | 41.9 | 36.0 | 17.3 | 14.9 | 22.9 | 7.0 | 11.8 | 6.2 | -1.2 |
   Previous cesarean delivery | 1.4 | 2.3 | 8.7 | 0.4 | -1.3 | -2.3 | -5.7 | -4.7 | -5.4 |
   Fetal anomaly | 6.5 | 0.7 | 0.5 | 0.1 | 0.3 | 0.1 | 5.7 | 0.3 | 0.1 |