Table 1. Maternal Characteristic According to Interpregnancy Interval in Sibling Pairs, Guangdong Province From 2014 to 2020.
| Characteristic | Interpregnancy interval, No. (%) | P value | |||||||
|---|---|---|---|---|---|---|---|---|---|
| All (N = 725 392) | <6 mo (n = 49 485) | 6-11 mo (n = 174 675) | 12-17 mo (n = 181 172) | 18-23 mo (n = 122 866) | 24-29 mo (n = 86 842) | 30-35 mo (n = 55 364) | ≥36 mo (n = 54 988) | ||
| Maternal age at first birth, y | |||||||||
| 20-24 | 374 582 (51.6) | 30 400 (61.4) | 99 926 (57.2) | 95 091 (52.5) | 59 918 (48.8) | 40 026 (46.1) | 24 883 (44.9) | 24 338 (44.3) | <.001 |
| 25-29 | 28 8325 (39.8) | 15 984 (32.3) | 62 394 (35.7) | 70 906 (39.1) | 51 384 (41.8) | 37 884 (43.6) | 24 690 (44.6) | 25 083 (45.6) | |
| 30-34 | 55 204 (7.6) | 2667 (5.4) | 10 824 (6.2) | 13 444 (7.4) | 10 226 (8.3) | 7900 (9.1) | 5128 (9.3) | 5015 (9.1) | |
| ≥35 | 7281 (1.0) | 434 (0.9) | 1531 (0.9) | 1731 (1.0) | 1338 (1.1) | 1032 (1.2) | 663 (1.2) | 552 (1.0) | |
| Maternal ethnicitya | |||||||||
| Han | 715 583 (98.7) | 48 966 (99.0) | 172 458 (98.7) | 178 801 (98.7) | 121 171 (98.6) | 85 578 (98.5) | 54 504 (98.5) | 54 105 (98.4) | <.001 |
| Otherb | 9809 (1.4) | 519 (1.1) | 2217 (1.3) | 2371 (1.3) | 1695 (1.4) | 1264 (1.5) | 860 (1.6) | 883 (1.6) | |
| Mode of delivery at first birth | |||||||||
| Cesarean delivery | 120 809 (16.7) | 1117 (2.3) | 10 440 (6.0) | 23 651 (13.1) | 26 685 (21.7) | 24 260 (27.9) | 16 870 (30.5) | 17 786 (32.4) | <.001 |
| Vaginal delivery | 604 583 (83.4) | 48 368 (97.7) | 164 235 (94.0) | 157 521 (87.0) | 96 181 (78.3) | 62 582 (72.1) | 38 494 (69.5) | 37 202 (67.7) | |
| Socioeconomic status, quintile | |||||||||
| 1 (Lowest) | 135 798 (18.7) | 9760 (19.7) | 35 932 (20.6) | 35 208 (19.4) | 22 354 (18.2) | 15 124 (17.4) | 9039 (16.3) | 8381 (15.2) | <.001 |
| 2 | 146 563 (20.2) | 13 101 (26.5) | 40 168 (23.0) | 37 401 (20.6) | 23 113 (18.8) | 15 258 (17.6) | 9033 (16.3) | 8489 (15.4) | |
| 3 | 151 635 (20.9) | 10 571 (21.4) | 37 311 (21.4) | 39 633 (21.9) | 25 842 (21.0) | 17 589 (20.3) | 10 765 (19.4) | 9924 (18.1) | |
| 4 | 145 584 (20.1) | 9714 (19.6) | 33 878 (19.4) | 36 494 (20.1) | 25 316 (20.6) | 17 725 (20.4) | 11 431 (20.7) | 11 026 (20.1) | |
| 5 (Highest) | 145 812 (20.1) | 6339 (12.8) | 27 386 (15.7) | 32 436 (17.9) | 26 241 (21.4) | 21 146 (24.4) | 15 096 (27.3) | 17 168 (31.2) | |
| Season of first birth | |||||||||
| Spring | 177 222 (24.4) | 10 051 (20.3) | 44 490 (25.5) | 40 364 (22.3) | 31 744 (25.8) | 20 380 (23.5) | 15 007 (27.1) | 15 186 (27.6) | <.001 |
| Summer | 179 468 (24.7) | 11 717 (23.7) | 46 237 (26.5) | 41 135 (22.7) | 33 472 (27.2) | 19 169 (22.1) | 15 681 (28.3) | 12 057 (21.9) | |
| Autumn | 182 389 (25.1) | 14 800 (29.9) | 41 776 (23.9) | 50 608 (27.9) | 28 952 (23.6) | 22 982 (26.5) | 12 177 (22.0) | 11 094 (20.2) | |
| Winter | 186 313 (25.7) | 12 917 (26.1) | 42 172 (24.1) | 49 065 (27.1) | 28 698 (23.4) | 24 311 (28.0) | 12 499 (22.6) | 16 651 (30.3) | |
a
Ethnicity was recorded in the data source.
b
Including 55 ethnic minority groups in China.