Table 1.
Baseline characteristics of the study population according to iron supplementation groups by stratum.
| Iron Supplementation Group | ||||||
|---|---|---|---|---|---|---|
| Stratum 1 | Stratum 2 | |||||
| 40 mg/d | 80 mg/d | p Value | 20 mg/d | 40 mg/d | p Value | |
| Characteristics | N = 261 | N = 268 | N = 130 | N = 132 | ||
| Age (years), mean ± SD | 30.7 ± 4.3 | 30.1 ± 5.3 | 0.217 | 30.2 ± 4.9 | 30.1 ± 5.6 | 0.812 |
| BMI (kg/m2), mean ± SD | 24.6 ± 4.1 | 24.7 ± 4.1 | 0.757 | 25.7 ± 5.3 | 25.8 ± 4.8 | 0.856 |
| BMI categories, n (%) | ||||||
| 18.5–24.9 (normal weight) | 198 (64) | 162 (60) | 74 (57) | 67 (51) | ||
| 25.0–29.9 (overweight) | 61 (24) | 74 (28) | 0.530 | 31 (24) | 42 (32) | 0.355 |
| ≥30 (obese) | 32 (12) | 32 (12) | 25 (19) | 23 (17) | ||
| GWG (kg), mean ± SD | 10.5 ± 3.5 | 10.3 ± 3.7 | 0.448 | 10.0 ± 3.9 | 10.5 ± 3.9 | 0.322 |
| Educational level, n (%) | ||||||
| Low (primary or less) | 88 (34) | 87 (32) | 46 (35) | 40 (30) | ||
| medium (secondary) | 103 (39) | 104 (39) | 0.882 | 47 (36) | 49 (37) | 0.639 |
| High (university or more) | 70 (27) | 77 (29) | 37 (29) | 43 (33) | ||
| Family SES, n (%) | ||||||
| Low | 39 (15) | 47 (18) | 24 (18) | 18 (14) | ||
| Medium | 174 (67) | 180 (67) | 0.521 | 87 (67) | 89 (67) | 0.431 |
| High | 48 (18) | 41 (15) | 19 (15) | 25 (19) | ||
| Cigarette smoking, n (%) | ||||||
| No | 222 (85) | 219 (82) | 0.302 | 104 (80) | 105 (80) | 0.927 |
| Yes | 39 (15) | 49 (18) | 26 (20) | 27 (20) | ||
| Alcohol consumption, n (%) | ||||||
| No | 213 (87) | 211 (87) | 0.934 | 106 (86) | 107 (89) | 0.479 |
| Yes | 32 (13) | 31 (13) | 17 (14) | 13 (11) | ||
| Physical activity (METs—min/week), n (%) | ||||||
| Sedentary/low (<600) | 49 (19) | 54 (20) | 28 (22) | 39 (30) | ||
| Moderate (≥600–1200) | 41 (16) | 39 (15) | 0.884 | 20 (15) | 14 (11) | 0.234 |
| High (≥1200) | 171 (66) | 175 (65) | 82 (63) | 79 (60) | ||
| Energy intake (kcal), mean ± SD | 2095 ± 460 | 2123 ± 477 | 0.510 | 2121 ± 544 | 2165 ± 528 | 0.522 |
| Dietary iron intake (mg), mean ± SD | 7.8 ± 2.7 | 7.7 ± 2.4 | 0.628 | 7.7 ± 2.8 | 7.6 ± 2.2 | 0.752 |
| Dietary vitamin C intake (mg), mean ± SD | 76.5 ± 33.8 | 78.3 ± 35.6 | 0.582 | 77.5 ± 38.5 | 75.4 ± 37.2 | 0.658 |
| Fiber intake (g), mean ± SD | 12.5 ± 4.6 | 12.7 ± 4.3 | 0.623 | 12.5 ± 5.1 | 12.2 ± 4.1 | 0.648 |
| Parity, n (%) | ||||||
| Primiparous | 94 (36) | 105 (39) | 0.473 | 57 (44) | 59 (45) | 0.890 |
| Multiparous | 166 (64) | 163 (61) | 73 (56) | 73 (55) | ||
| Iron status characteristics | ||||||
| Hb (g/L), mean ± SD | 123.4 ± 4.7 | 123.3 ± 5.3 | 0.690 | 136.6 ± 4.4 | 135.7 ± 4.6 | 0.101 |
| SF (µg/L), mean ± SD * | 32.1 ± 2.0 | 32.8 ± 2.1 | 0.740 | 34.8 ± 1.9 | 34.8 ± 1.9 | 0.965 |
| Iron deficiency, n (%) ** | 37 (14) | 38 (14) | 0.999 | 16 (12) | 19 (14) | 0.620 |
| Carrier of HFE gene mutation, n (%) | 62 (30) | 74 (36) | 0.164 | 32 (30) | 40 (38) | 0.192 |
| H63D mutation, n (%) | 51 (24) | 63 (31) | 0.150 | 29 (27) | 34 (32) | 0.377 |
| S65C/C282Y mutation, n (%) | 13 (6) | 14 (7) | 0.802 | 3 (3) | 8 (8) | 0.110 |
| Cortisol (µg/dl), mean ± SD | 17.6 ± 4.7 | 18.4 ± 4.6 | 0.064 | 18.6 ± 5.5 | 18.3 ± 5.2 | 0.693 |
Values are mean ± SD or number (%). Abbreviations: BMI—body mass index; GWG—gestational weight gain; SES—socioeconomic status; METs—metabolic equivalent of task; Hb—hemoglobin; SF—serum ferritin; HFE—hemochromatosis. p-value for the differences across supplementation dose as derived from independent samples Student’s T-test or chi-square test. The reference group was 40 mg/d dose group for stratum 1 and 20 mg/d dose group for stratum 2. * Geometric means of log-transformed. ** Defined as a serum ferritin concentration SF < 15 µg/L according to WHO definition.