- Results arising from univariate analysis of the risk factors for PTB.
| Characteristics | Total n=2942 | Preterm n=1471 | Term n=1471 | P-value |
|---|---|---|---|---|
| Supplementation of FA in early pregnancy | ||||
| No | 1045 (35.5) | 589 (40.0) | 1456 (31.0) | <0.001 |
| Full | 1897 (64.5) | 882 (60.0) | 1015 (69.0) | |
| Preeclampsia | ||||
| No | 2721 (92.5) | 1272 (86.5) | 21449 (98.5) | <0.001 |
| Yes | 221 (7.5) | 199 (13.5) | 122 (1.5) | |
| Smoking in pregnancy | ||||
| No | 2758 (93.7) | 1354 (92.0) | 1404 (95.4) | <0.001 |
| Yes | 184 (6.3) | 117 (8.0) | 67 (4.6) | |
| Previous preterm birth | ||||
| No | 2830 (96.2) | 1377 (93.6) | 1453 (98.8) | <0.001 |
| Yes | 112 (3.8) | 94 (6.4) | 18 (1.2) | |
| Diabetes mellitus in pregnancy | ||||
| No | 2438 (82.9) | 1176 (79.9) | 1262 (85.8) | <0.001 |
| Yes | 504 (17.1) | 295 (20.1) | 209 (14.2) | |
| Chronic renal disease | ||||
| No | 2940 (99.9) | 1469 (99.9) | 1471 (100) | 0.157 |
| Yes | 2 (0.1) | 2 (0.1) | 0 (0) | |
| Hypothyroidism | ||||
| No | 2790 (94.8) | 1398 (95.0) | 1392 (94.6) | 0.617 |
| Yes | 152 (5.2) | 73 (5.0) | 79 (5.4) | |
| Placenta problems | ||||
| No | 2569 (88.2) | 1194 (81.2) | 1402 (95.3) | <0.001 |
| Yes | 346 (11.8) | 277 (18.8) | 69 (4.7) | |
| Pre-pregnancy BMI (kg/m2) | ||||
| <24 | 2396 (81.4) | 1178 (80.1) | 1218 (82.8) | 0.058 |
| ≥24 | 546 (18.6) | 293 (19.9) | 253 (17.2) | |
| Assisted reproduction | ||||
| No | 2744 (93.3) | 1363 (92.7) | 1381 (93.9) | 0.185 |
| Yes | 198 (6.7) | 108 (7.3) | 90 (6.1) | |
| Prenatal examination | ||||
| No | 216 (7.3) | 97 (6.6) | 119 (8.1) | 0.120 |
| Yes | 2726 (92.7) | 1374 (93.4) | 1352 (91.9) | |
| Supplementation of folic acid before pregnancy | ||||
| No | 1592 (54.1) | 859 (58.4) | 733 (49.8) | <0.001 |
| Partial | 501 (17.0) | 229 (15.6) | 272 (18.5) | |
| Full | 849 (28.9) | 383 (26.0) | 466 (31.7) | |
| Family history of hypertension | ||||
| No | 2864 (97.3) | 1427 (97.0) | 1437 (97.9) | 0.251 |
| Yes | 78 (2.7) | 44 (3.0) | 34 (2.3) | |
| Values are presented as numbers and percentages (%). PTB: preterm birth, FA: folic acid, BMI: body mass index | ||||