Table 1 Characteristics of subjects in Liuzhou city, Guangxi Province
Characteristics | Infants with BDs n (%) | Normal infants n (%) | χ2 | P |
|---|---|---|---|---|
Maternal age (years) | ||||
  < 20 | 19(3.0%) | 936 (2.9%) | 11.10 | < 0.01 |
 20 ~ | 73 (11.5%) | 4271 (13.4%) |  |  |
 25 ~ | 191 (30.1%) | 10,359 (32.5%) |  |  |
 30 ~ | 199 (31.3%) | 10,517 (33.0%) |  |  |
  ≥ 35 | 153 (24.1%) | 5831 (18.3%) |  |  |
Family income (RMB per capita) | ||||
  < 2000 | 156 (24.6%) | 7662 (23.5%) | 2.54 | 0.16 |
 2000~ | 107 (16.8%) | 5087 (15.6%) |  |  |
 4000~ | 250 (39.4%) | 13,147 (40.4%) |  |  |
  ≥ 8000~ | 123 (19.4%) | 6653 (20.4%) |  |  |
Maternal education | ||||
 Primary or below | 28 (4.4%) | 128 (0.4%) | 9.49 | 0.00 |
 Middle school | 184 (29.0%) | 11,567 (35.5%) |  |  |
 High or technical school | 124 (19.5%) | 10,543 (32.4%) |  |  |
 College or above | 299 (47.1%) | 10,311 (31.7%) |  |  |
Birth weight(g) | ||||
  < 1500 g | 316 (49.8%) | 194 (0.6%) | 2723.66 | < 0.01 |
 1500 g ~ | 52 (8.2%) | 1799 (5.6%) |  |  |
 2500 g ~ | 201 (31.6%) | 22,424 (70.3%) |  |  |
  ≥ 3500 g | 66 (10.4%) | 7497 (23.5%) |  |  |
Infant gender | ||||
 Male | 361 (56.8%) | 16,790 (52.6%) | 14.50 | < 0.01 |
 Female | 233 (36.7%) | 15,124 (47.4%) |  |  |
 Unknown gender | 41 (6.5%) | 0 (0.0%) |  |  |
Number of pregnancies | ||||
 1 | 110 (17.3%) | 6591 (20.7%) | 1.30 | 0.25 |
 2 | 175 (27.6%) | 9130 (28.6%) |  |  |
  ≥ 3 | 350 (55.1%) | 16,193 (50.7%) |  |  |
Total previous live births | ||||
 0 | 97 (15.3%) | 21 (0.1%) | 740.78 | < 0.01 |
 1 | 304 (47.9%) | 12,259 (38.4%) |  |  |
  ≥ 2 | 234 (36.8%) | 19,634 (61.5%) |  |  |
Residence | ||||
 Urban | 250 (39.4%) | 15,510 (48.6%) | 15.50 | < 0.01 |
 Rural | 385 (60.6%) | 16,404 (51.4%) |  |  |