Table 2.
Prepregnancy dietary iron intakes and RRs of GDM among 13,475 women
| Quintiles of iron intake (median, mg/day) | Total (n) | Cases (n) | Age-adjusted | Multivariate-adjusted | ||
|---|---|---|---|---|---|---|
| 13,475 | 867 | RR (95% CI) | P value | RR (95% CI)* | P value | |
| Heme iron | ||||||
| Q1 (0.66) | 2,581 | 122 | 1.00 (ref) | n/a | 1.00 (ref) | n/a |
| Q2 (0.90) | 2,987 | 168 | 1.20 (0.95–1.52) | 0.13 | 1.11 (0.87–1.43) | 0.40 |
| Q3 (1.10) | 2,933 | 171 | 1.42 (1.13–1.78) | 0.003 | 1.31 (1.03–1.68) | 0.03 |
| Q4 (1.30) | 2,779 | 201 | 1.74 (1.39–2.19) | <0.0001 | 1.51 (1.17–1.93) | 0.001 |
| Q5 (1.60) | 2,195 | 205 | 2.13 (1.70–2.67) | <0.0001 | 1.58 (1.21–2.08) | 0.001 |
| Trend | <0.0001 | 0.0001 | ||||
| Total iron | ||||||
| Q1 (10.70) | 2,380 | 180 | 1.00 (ref) | n/a | 1.00 (ref) | n/a |
| Q2 (13.00) | 2,128 | 161 | 0.85 (0.68–1.07) | 0.17 | 0.86 (0.68–1.10) | 0.24 |
| Q3 (16.13) | 2,376 | 144 | 0.80 (0.64–1.00) | 0.05 | 0.85 (0.67–1.09) | 0.20 |
| Q4 (24.15) | 2,673 | 154 | 0.72 (0.58–0.90) | 0.004 | 0.84 (0.66–1.07) | 0.15 |
| Q5 (49.80) | 3,918 | 228 | 0.78 (0.64–0.96) | 0.02 | 0.90 (0.72–1.12) | 0.33 |
| Trend | 0.12 | 0.95 | ||||
| Dietary total iron | ||||||
| Q1 (10.30) | 2,708 | 183 | 1.00 (ref) | n/a | 1.00 (ref) | n/a |
| Q2 (11.90) | 2,695 | 211 | 1.00 (0.82–1.23) | 0.99 | 0.99 (0.80–1.24) | 0.96 |
| Q3 (13.30) | 2,506 | 148 | 0.77 (0.62–0.95) | 0.02 | 0.83 (0.66–1.06) | 0.14 |
| Q4 (15.00) | 2,684 | 163 | 0.84 (0.68–1.04) | 0.11 | 0.97 (0.77–1.24) | 0.83 |
| Q5 (18.90) | 2,882 | 162 | 0.83 (0.68–1.02) | 0.08 | 1.12 (0.87–1.45) | 0.38 |
| Trend | 0.05 | 0.26 | ||||
| Supplemental iron | ||||||
| Q1 (0) | 7,949 | 544 | 1.00 (ref) | n/a | 1.00 (ref) | n/a |
| Q2 (5.10) | 603 | 40 | 0.96 (0.76–1.22) | 0.76 | 0.98 (0.76–1.25) | 0.84 |
| Q3 (15.00) | 1,654 | 95 | 0.89 (0.72–1.11) | 0.30 | 0.95 (0.76–1.19) | 0.66 |
| Q4 (30.00) | 1,134 | 59 | 0.80 (0.64–1.01) | 0.07 | 0.86 (0.68–1.10) | 0.23 |
| Q5 (60.00) | 2,135 | 129 | 0.99 (0.81–1.20) | 0.89 | 1.04 (0.84–1.28) | 0.72 |
| Trend | 0.56 | 0.97 | ||||
| Nonheme iron | ||||||
| Q1 (7.58) | 2,324 | 184 | 1.00 (ref) | n/a | 1.00 (ref) | n/a |
| Q2 (10.55) | 2,189 | 153 | 0.86 (0.69–1.08) | 0.20 | 0.95 (0.74–1.22) | 0.68 |
| Q3 (13.39) | 2,381 | 150 | 0.80 (0.64–1.00) | 0.05 | 0.92 (0.71–1.19) | 0.52 |
| Q4 (21.03) | 2,648 | 147 | 0.69 (0.55–0.86) | 0.001 | 0.85 (0.67–1.10) | 0.21 |
| Q5 (45.33) | 3,933 | 233 | 0.79 (0.65–0.96) | 0.02 | 0.97 (0.78–1.20) | 0.75 |
| Trend | 0.15 | 0.86 |
*Covariates include age, parity, BMI, physical activity, glycemic load, polyunsaturated fat intake, cereal fiber, smoking, alcohol, total calories, and family history of diabetes. n/a, not applicable.