Table 2.
Prepregnancy Folate Intake and Relative Risks of Spontaneous Abortion
| Categories of Folate Intake (median, μg/day) | Cases/Total | % | Age, Year, & Energy- Adjusted RR (95% CI)* | Multivariate-Adjusted RR (95% CI)† |
|---|---|---|---|---|
| Total folate | ||||
| Q1 (238) | 537/3185 | 16.9 | 1.00 (Ref) | 1.00 (Ref) |
| Q2 (330) | 572/3192 | 17.9 | 1.03 (0.92, 1.14) | 1.02 (0.92, 1.14) |
| Q3 (470) | 559/3197 | 17.5 | 0.99 (0.89, 1.10) | 0.99 (0.89, 1.10) |
| Q4 (703) | 562/3186 | 17.6 | 0.97 (0.88, 1.08) | 0.98 (0.88, 1.09) |
| Q5 (1128) | 526/3190 | 16.5 | 0.91 (0.82, 1.01) | 0.91 (0.82, 1.02) |
| P for trend | 0.03 | 0.04 | ||
| Folate from foods | ||||
| Q1 (213) | 514/3177 | 16.2 | 1.00 (Ref) | 1.00 (Ref) |
| Q2 (267) | 497/3180 | 15.6 | 0.96 (0.86, 1.08) | 0.97 (0.86, 1.08) |
| Q3 (311) | 551/3204 | 17.2 | 1.03 (0.93, 1.15) | 1.03 (0.93, 1.15) |
| Q4 (364) | 576/3199 | 18.0 | 1.04 (0.94, 1.16) | 1.05 (0.94, 1.17) |
| Q5 (461) | 618/3190 | 19.4 | 1.06 (0.95, 1.18) | 1.07 (0.96, 1.19) |
| P for trend | 0.12 | 0.09 | ||
| Folate from supplements | ||||
| Q1 (0) | 1145/6638 | 17.3 | 1.00 (Ref) | 1.00 (Ref) |
| Q2 (228) | 701/3779 | 18.6 | 0.95 (0.87, 1.03) | 0.95 (0.87, 1.03) |
| Q3 (400) | 589/3351 | 17.6 | 0.95 (0.87, 1.04) | 0.95 (0.87, 1.04) |
| Q4 (1000) | 321/2182 | 14.7 | 0.80 (0.71, 0.89) | 0.80 (0.71, 0.90) |
| P for trend | <0.001 | <0.001 | ||
RR, relative risk; CI, confidence interval. Ranges for total folate quintiles in μg/day: Q1 (<284.9), Q2 (285–383.9), Q3 (384–580.9), Q4 (581–850.9), Q5 (>851). Ranges for food folate quintiles in μg/day: Q1 (<243.9), Q2 (244–288.9), Q3 (289–336.9), Q4 (337–398.9), Q5 (>399). Ranges for supplemental folate quartiles in μg/day: Q1 (0), Q2 (0.1–399.9), Q3 (400–729.9), Q4 (>730).
Adjusted for age (continuous), total energy intake (continuous), and year (continuous).
Age, year, and energy adjusted model further adjusted for body mass index (<18.5, 18.5–24.9, 25–29.9, ≥30, and missing), smoking status (never, former, current, and missing), physical activity (< 3 metabolic equivalent task [MET]-h/wk, 3–8.9 MET-h/wk, 9–17.9 MET-h/wk, 18–26.9 MET-h/wk, 27–41.9 MET-h/wk, >42 MET-h/wk, and missing), history of infertility (no, yes, and missing), marital status (married, not married), and race (white, other).