Table 1.
Characteristics of study population.
| Characteristic | Reference group | Excluded group | Total (n = 2,906,804) | P value |
|---|---|---|---|---|
| (n = 2,255,989, 77.6%) | (n = 650,815, 22.4%) | |||
| n (%) | n (%) | n | ||
| Maternal age | < 0.001 | |||
| > 35 | 1,865,784 (82.7) | 484,833 (74.5) | 2,350,617 | |
| ≥ 35 | 390,205 (17.3) | 165,982 (25.5) | 556,187 | |
| Year | < 0.001 | |||
| 2004–2011 | 1,145,010 (50.8) | 286,277 (44) | 1,431,287 | |
| 2012–2019 | 1,110,979 (49.2) | 364,538 (56) | 1,475,517 | |
| Gender | < 0.001 | |||
| Female | 1,092,683 (48.4) | 301,211 (46.3) | 1,393,894 | |
| Male | 1,163,306 (51.6) | 349,604 (53.7) | 1,512,910 | |
| Delivery method | < 0.001 | |||
| Vaginal delivery | 1,531,110 (67.9) | 385,852 (59.3) | 1,916,962 | |
| Cesarean section | 724,879 (32.1) | 264,963 (40.7) | 989,842 | |
| Gestational age, wk | < 0.001 | |||
| 24–27 + 6 | 1817 (0.1) | 3408 (0.5) | 5225 | |
| 28–31 + 6 | 5740 (0.3) | 7324 (1.1) | 13,064 | |
| 32–33 + 6 | 9764 (0.4) | 7790 (1.2) | 17,554 | |
| 34–36 + 6 | 118,790 (5.3) | 55,351 (8.5) | 174,141 | |
| ≥ 37 | 2,119,878 (94) | 576,942 (88.6) | 2,696,820 | |
| Birthweight, g | < 0.001 | |||
| < 1000 | 1749 (0.1) | 3616 (0.6) | 5365 | |
| 1000–1999 | 17,922 (0.8) | 17,768 (2.7) | 35,690 | |
| 2000–2999 | 836,347 (37.1) | 254,471 (39.1) | 1,090,818 | |
| 3000–3999 | 1,364,258 (60.5) | 361,453 (55.5) | 1,725,711 | |
| ≥ 4000 | 35,713 (1.6) | 13,507 (2.1) | 49,220 | |
| Perinatal mortality | < 0.001 | |||
| Death 24 h | 18 (0) | 9 (0) | 27 | |
| Death 2–7 days | 16 (0) | 7 (0) | 23 | |
| Death 8–28 days | 1541 (0.1) | 605 (0.1) | 2146 | |
| Death 29–365 days | 3080 (0.1) | 2460 (0.4) | 5540 | |
| Death > 365 days | 2313 (0.1) | 1827 (0.3) | 4140 | |
| Alive | 2,249,021 (99.7) | 645,907 (99.2) | 2,894,928 |