- Individual and joint effects of no FA supplementation and preeclampsia on PTB and measures of interaction.
| Variable | Case/control number | aOR value | 95% CI | P-value | RERI | AP | S |
|---|---|---|---|---|---|---|---|
| All preterm birth (n=1471)/control group (n=1471) | |||||||
| None OR00 | 784/1001 | 1.000 | |||||
| No FA supplementation OR01 | 488/448 | 1.290* | 1.026-1.623 | <0.001 | |||
| Preeclampsia OR10 | 98/14 | 9.463 | 5.090-17.60 | 0.027 | |||
| No FA supplementation + preeclampsia OR11 | 101/8 | 12.138* | 5.726-25.73 | <0.001 | 2.385 | 0.19 | 1.27 |
| Iatrogenic preterm birth (n=655)/paired control group (n=655) | |||||||
| None OR00 | 304/452 | 1.000 | |||||
| No FA supplementation OR01 | 165/190 | 1.385 | 0.938-2.047 | 0.180 | |||
| Preeclampsia OR10 | 91/8 | 19.680* | 8.462-45.77 | <0.001 | |||
| No FA supplementation + preeclampsia OR11 | 95/5 | 23.412* | 8.882-60.71 | <0.001 | 3.347 | 0.14 | 1.18 |
| Spontaneous preterm birth (n=816)/paired control group (n=816) | |||||||
| None OR00 | 480/549 | 1.000 | |||||
| No FA supplementationOR01 | 323/258 | 1.353* | 1.009-1.814 | 0.043 | |||
| Preeclampsia OR10 | 7/6 | 1.140 | 0.317-4.106 | 0.841 | |||
| No FA supplementation + preeclampsia OR11 | 6/3 | 2.056 | 0.471-8.984 | 0.338 | - | - | - |
Conditional logistic regression analysis was carried out. The control group was the reference group. Taking preeclampsia and folic acid supplementation in early pregnancy as independent variables, patients were divided into 4 groups: no preeclampsia and folic acid supplementation (0.4-0.8 mg/d for 12 weeks) in early pregnancy (OR00), no preeclampsia and no FA supplementation in early pregnancy (OR01), preeclampsia and folic acid supplementation (0.4-0.8 mg/d for 12 weeks) in early pregnancy (OR10), preeclampsia and no FA supplementation in early pregnancy (OR11), no preeclampsia and FA supplementation (0.4-0.8 mg/d for 12 weeks) in early pregnancy (OR00) were used as the reference group. Adjusted ORs (aOR) were calculated by adjusted confounding factors, maternal age, parity, maternal education, residence, smoking in pregnancy, previous preterm birth, diabetes mellitus in pregnancy, placenta problems, supplementation of folic acid before pregnancy, assisted reproduction, pre-pregnancy BMI.
↵* p<0.05 was significant.FA: folic acid, BMI: body mass index, RERI: excess relative risk of interaction effect, AP: proportion attributable to interaction, S: synergy index, CI: confidence interval