- Multivariate conditional logistic regression analysis of risk factors for all preterm birth (PTB).
| Variable | aOR Value | 95% CI | P-value |
|---|---|---|---|
| Maternal age | |||
| <20 | 1.039 | 0.835-1.293 | 0.732 |
| 20-34 | 1.000 | ||
| ≥35 | 2.136* | 1.101-4.142 | 0.025 |
| Parity | |||
| Multipara | 1.230* | 1.039-1.507 | 0.030 |
| Race | |||
| Han | 1.000 | ||
| Others | 1.387 | 0.902-2.133 | 0.160 |
| Maternal education | |||
| Middle school or below | 1.459* | 1.122-1.898 | 0.005 |
| High school | 1.407* | 1.126-1.759 | 0.003 |
| University or above | 1.000 | ||
| Residence during pregnancy | |||
| City | 1.000 | ||
| Small town | 1.352* | 1.094-1.670 | 0.005 |
| countryside | 1.686* | 1.212-2.346 | 0.002 |
| Family income monthly per person (yuan) | |||
| <2,000 | 1.037 | 0.680-1.582 | 0.725 |
| 2,000-10,000 | 0.996 | 0.966-1.220 | 0.770 |
| >10,000 | 1.000 | ||
| Supplementation of FA in early pregnancy | |||
| No | 1.351* | 1.073-1.701 | 0.011 |
| Full | 1.000 | ||
| Preeclampsia | |||
| Yes | 9.684* | 5.967-15.716 | <0.001 |
| Smoking in pregnancy | |||
| Yes | 1.691* | 1.168-2.447 | 0.007 |
| Previous preterm birth | |||
| Yes | 4.566* | 2.620-7.959 | <0.001 |
| diabetes mellitus in pregnancy | |||
| Yes | 1.431* | 1.146-1.786 | 0.002 |
| Placenta problems | |||
| Yes | 11.634* | 6.661-20.320 | <0.001 |
| Pre-pregnancy BMI (kg/m2) | |||
| ≥24 | 0.870 | 0.699-1.084 | 0.204 |
| Assisted reproduction | |||
| Yes | 1.235 | 0.878-1.740 | 0.226 |
| Supplementation of folic acid before pregnancy | |||
| No | 1.068 | 0.927-1.231 | 0.360 |
| Partial | 0.987 | 0.837-1.160 | 0.880 |
| Full | 1.000 | ||
Conditional logistic regression analysis was performed. The control group was the reference group.
↵* p<0.05 was significant. aOR value and 95% CI after adjusting other confounders (including parity, maternal age, race, maternal education, residence during pregnancy, family income monthly per person, FA supplementation in early pregnancy, FA supplementation before pregnancy, preeclampsia, smoking in pregnancy, previous preterm history, diabetes mellitus in pregnancy, and placenta problems, pre-pregnancy BMI, and assisted reproduction). CI: confidence interval, BMI: body mass index, aOR: adjusted odds ratio, FA: folic acid