Table 1 Socio-demographic and pre-pregnancy characteristics of study participants
Variables | Overall | Maternal age groups (years) | p | |||
|---|---|---|---|---|---|---|
20–24 | 25–29 | 30–34 | ≥35 | |||
(n) | (10,171) | (3274) | (4587) | (1637) | (572) | |
Residential area (n, %) | < 0.001 | |||||
Urban | 1437 (14.1) | 396 (12.1) | 742 (16.2) | 222 (13.6) | 68 (11.9) | |
Rural | 8734 (85.9) | 2878 (87.9) | 3845 (83.8) | 1415 (86.4) | 504 (88.1) | |
Family per capita annual income (Chinese Yuan, n, %) | 0.004 | |||||
≤ 10,000 | 1647 (16.2) | 550 (16.8) | 684 (14.9) | 267 (16.3) | 124 (21.7) | |
10,001–20,000 | 4147 (40.8) | 1409 (43.0) | 1805 (39.4) | 660 (40.3) | 223 (39.0) | |
20,001–30,000 | 2871 (28.2) | 922 (28.2) | 1345 (29.3) | 442 (27.0) | 141 (24.7) | |
≥ 30,001 | 1506 (14.8) | 393 (12.0) | 753 (16.4) | 268 (16.4) | 84 (14.7) | |
Education level (n, %) | < 0.001 | |||||
Junior high school or lower | 8511 (83.7) | 2822 (86.2) | 3604 (78.6) | 1456 (88.9) | 532 (93.0) | |
High school/college | 1660 (16.3) | 452 (13.8) | 983 (21.4) | 181 (11.1) | 40 (7.0) | |
Occupation (n, %) | < 0.001 | |||||
Farmer | 1413 (13.9) | 398 (12.2) | 582 (12.7) | 285 (17.4) | 134 (23.4) | |
Housewife | 5521 (54.3) | 1768 (54.0) | 2447 (53.3) | 924 (56.4) | 317 (55.4) | |
Factory worker | 2395 (23.5) | 819 (25.0) | 1121 (24.4) | 339 (20.7) | 97 (17.0) | |
Other | 842 (8.3) | 289 (8.8) | 437 (9.5) | 89 (5.4) | 24 (4.2) | |
Pre-pregnancy BMI (kg/m2, n, %) | < 0.001 | |||||
< 18.5 | 1834 (18.0) | 713 (21.8) | 836 (18.2) | 205 (12.5) | 50 (8.7) | |
18.5–23 | 6247 (61.4) | 2028 (61.9) | 2854 (62.2) | 994 (60.7) | 317 (55.4) | |
23–27.5 | 1792 (17.6) | 461 (14.1) | 764 (16.7) | 382 (23.3) | 168 (29.4) | |
≥ 27.5 | 298 (2.9) | 72 (2.2) | 133 (2.9) | 56 (3.4) | 37 (6.5) | |
Gravidity (n, %) | < 0.001 | |||||
None | 3878 (38.1) | 1861 (56.8) | 1708 (37.2) | 203 (12.4) | 26 (4.5) | |
Once or more pregnancies | 6293 (61.9) | 1413 (43.2) | 2879 (62.8) | 1434 (87.6) | 546 (95.5) | |
Parity (n, %) | < 0.001 | |||||
None | 5354 (52.6) | 2445 (74.7) | 2406 (52.5) | 344 (21.0) | 65 (11.4) | |
Once or more births | 4817 (47.4) | 829 (25.3) | 2181 (47.5) | 1293 (79.0) | 507 (88.6) | |
History of miscarriage (n, %) | < 0.001 | |||||
None | 6903 (67.9) | 2506 (76.5) | 3129 (68.2) | 927 (56.6) | 256 (44.8) | |
Once | 1988 (19.5) | 563 (17.2) | 891 (19.4) | 390 (23.8) | 130 (22.7) | |
Twice or more times | 1280 (12.6) | 205 (6.3) | 567 (12.4) | 320 (19.5) | 186 (32.5) | |
History of induced abortion (n, %) | < 0.001 | |||||
None | 9854 (96.9) | 3218 (98.3) | 4451 (97.0) | 1546 (94.4) | 538 (94.1) | |
Once or more times | 317 (3.1) | 56 (1.7) | 136 (3.0) | 91 (5.6) | 34 (5.9) | |
History of preterm labor (n, %) | 0.007 | |||||
None | 10,110 (99.4) | 3262 (99.6) | 4562 (99.5) | 1620 (99.0) | 565 (98.8) | |
Once or more times | 61 (0.6) | 12 (0.4) | 25 (0.5) | 17 (1.0) | 7 (1.2) | |