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Comparisons of baseline characteristics between the case and control groups
| Characteristic | Case group (n=507 couples) | Control group (n=465 couples) | t/χ2 | P |
|---|---|---|---|---|
| Mean age (years) | 29.3 ± 4.7 | 28.4 ± 3.3 | 1.142 | 0.254 |
| Obesity (yes/no) | 136/371 | 131/334 | 0.221 | 0.638 |
| Smoking (yes/no) | 248/259 | 218/247 | 0.402 | 0.526 |
| Drinking (yes/no) | 245/262 | 221/244 | 0.062 | 0.804 |
