Table 1.
Baseline characteristics in case and control groupsa
| Baseline characteristics | Control group (n = 504) | Case group (n = 464) | Univariate analysisd |
|---|---|---|---|
| Age at pregnancy onset (years) | χ2 = 0.191; P = 0.662 | ||
| < 35 | 434(86.1%) | 404(87.1%) | |
| ≥ 35 | 70(13.9%) | 60(12.9%) | |
| Residence location | χ2 = 39.390; P < 0.001 | ||
| Rural areas | 276(54.8%) | 344(74.1%) | |
| Urban areas | 228(45.2%) | 120(25.9%) | |
| Education level (years) | Z = 12.306; P < 0.001b | ||
| ≤ 9 | 6(1.2%) | 66(14.2%) | |
| 9–12 | 100(19.8%) | 190(40.9%) | |
| 12–16 | 168(33.3%) | 130(28.0%) | |
| > 16 | 230(45.6%) | 78(16.8%) | |
| Annual income in the past 1 year (RMB) | Z = 15.946; P < 0.001b | ||
| ≤ 50,000 | 144(28.6%) | 372(80.2%) | |
| 50,000-100,000 | 216(42.9%) | 68(14.7%) | |
| 100,000-150,000 | 46(9.1%) | 10(2.2%) | |
| > 150,000 | 98(19.4%) | 14(3.0%) | |
| History of adverse pregnancy outcomes | χ2 = 12.033; P = 0.001 | ||
| No | 280(55.6%) | 206(44.4%) | |
| Yes | 224(44.4%) | 258(55.6%) | |
| Consanguineous marriage | χ2 = 14.480; P < 0.001 | ||
| No | 502(99.6%) | 446(96.1%) | |
| Yes | 2(0.4%) | 18(3.9%) | |
| History of congenital heart disease in family | χ2 = 20.759; P < 0.001 | ||
| No | 500(99.2%) | 436(94.0%) | |
| Yes | 4(0.8%) | 28(6.0%) | |
| Cold or feverc | χ2 = 16.513; P < 0.001 | ||
| No | 446(88.5%) | 366(78.9%) | |
| Yes | 58(11.5%) | 98(21.1%) | |
| Drinking alcoholc | χ2 = 9.060; P = 0.003 | ||
| No | 468(92.9%) | 404(87.1%) | |
| Yes | 36(7.1%) | 60(12.9%) | |
| Drinking teac | χ2 = 9.257; P = 0.002 | ||
| No | 402(79.8%) | 404(87.1%) | |
| Yes | 102(20.2%) | 60(12.9%) | |
| Living near environmental pollution sourcec | χ2 = 38.443; P < 0.001 | ||
| No | 470(93.3%) | 370(79.7%) | |
| Yes | 34(6.7%) | 94(20.3%) | |
| Dyeing hair or permingc | χ2 = 12.532; P < 0.001 | ||
| No | 474(94.0%) | 406(87.5%) | |
| Yes | 30(6.0%) | 58(12.5%) | |
| Folatec | χ2 = 23.917; P < 0.001 | ||
| No | 34(6.7%) | 78(16.8%) | |
| Yes | 470(93.3%) | 386(83.2%) | |
| Decorating housingc | χ2 = 2.757; P = 0.097 | ||
| No | 462(91.7%) | 438(94.4%) | |
| Yes | 42(8.3%) | 26(5.6%) | |
aData presented as number (percentage) unless otherwise indicated
bThe Wilcoxon rank-sum test method was used; otherwise, the χ2 test was used
cThe exposure occurred in the periconceptional period
dP < 0.05 was considered to indicate a statistically significant difference