TABLE 1.
Characteristics of the study population by early pregnancy serum ferritin quintiles (n = 5983)1
| Total group | Serum ferritin quintile 1 | Serum ferritin quintile 2 | Serum ferritin quintile 3 | Serum ferritin quintile 4 | Serum ferritin quintile 5 | ||
|---|---|---|---|---|---|---|---|
| n = 5983 | n = 1196 | n = 1197 | n = 1196 | n = 1198 | n = 1196 | P value2 | |
| Serum ferritin, range, μg/L | 2–390 | 2–26 | 26–42 | 42–63 | 63–96 | 96–390 | |
| Serum ferritin, μg/L | 52.2 [9.9, 203.7] | 17.3 [6.7, 25.9] | 34.2 [26.8, 42.1] | 52.2 [42.8, 62.4] | 76.2 [63.3, 94.2] | 128.4 [96.5, 295.7] | <0.001 |
| TSAT, % | 24.5 ± 10.5 | 18.4 ± 8.9 | 24.0 ± 8.9 | 26.1 ± 9.9 | 26.3 ± 10.4 | 28.0 ± 11.7 | <0.001 |
| Iron, μmol/L | 17.1 ± 6.6 | 14.7 ± 6.5 | 17.5 ± 6.0 | 17.9 ± 6.3 | 17.6 ± 6.5 | 18.0 ± 7.0 | <0.001 |
| Transferrin, g/L | 2.9 ± 0.5 | 3.3 ± 0.5 | 3.0 ± 0.4 | 2.8 ± 0.4 | 2.7 ± 0.4 | 2.6 ± 0.3 | <0.001 |
| Hemoglobin, g/dL | 12.3 ± 0.9 | 12.0 ± 1.0 | 12.3 ± 0.9 | 12.4 ± 0.9 | 12.4 ± 0.9 | 12.4 ± 0.9 | <0.001 |
| CRP, mg/L | 4.5 [0.6, 25.7] | 4.8 [0.7,23.6] | 4.4 [0.6,22.1] | 4.4 [0.7,24.4] | 4.3 [0.6,29.1] | 4.4 [0.5,32.8] | <0.001 |
| Maternal age at enrolment, years | 29.7 ± 5.1 | 29.0 ± 5.6 | 29.4 ± 5.3 | 29.8 ± 5.0 | 30.1 ± 4.8 | 30.5 ± 4.4 | <0.001 |
| Parity, nulliparous, n (%) | 3399 (56.8) | 481 (40.2) | 602 (50.3) | 682 (57.0) | 764 (63.8) | 870 (72.7) | <0.001 |
| Prepregnancy BMI, kg/m2 | 23.5 ± 4.2 | 23.5 ± 4.1 | 23.3 ± 4.2 | 23.3 ± 4.0 | 23.6 ± 4.2 | 23.9 ± 4.4 | <0.001 |
| Gestational age at blood sampling, weeks | 13.2 [9.6, 17.6] | 13.9 [7.6, 17.9] | 13.5 [9.5, 17.7] | 13.2 [9.6, 17.4] | 12.9 [9.5, 17.4] | 12.8 [9.5, 17.1] | <0.001 |
| Higher education, n (%) | 2501 (41.8) | 369 (30.9) | 467 (39.0) | 533 (44.6) | 546 (45.6) | 586 (49.0) | <0.001 |
| European ethnicity,3 n (%) | 3500 (61.0) | 470 (39.3) | 668 (55.8) | 740 (61.9) | 797 (66.5) | 825 (69.0) | <0.001 |
| Continued smoking during pregnancy, n (%) | 990 (16.5) | 188 (15.7) | 228 (19.0) | 212 (17.7) | 195 (16.3) | 167 (14.0) | <0.05 |
| Folic acid supplement use, n (%) | 3413 (57.0) | 532 (44.5) | 634 (53.0) | 703 (58.8) | 755 (63.0) | 789 (66.0) | <0.001 |
| Systolic blood pressure, mmHg | |||||||
| Early pregnancy | 115.3 ± 12.0 | 113.5 ± 11.9 | 114.8 ± 11.8 | 115.1 ± 11.8 | 115.9 ± 12.0 | 116.9 ± 12.3 | <0.001 |
| Mid pregnancy | 116.9 ± 11.8 | 115.5 ± 11.6 | 116.1 ± 11.6 | 116.9 ± 11.5 | 117.2 ± 12.1 | 118.9 ± 11.9 | <0.001 |
| Late pregnancy | 118.3 ± 11.8 | 116.5 ± 11.6 | 117.3 ± 11.4 | 118.6 ± 12.2 | 119.0 ± 12.0 | 119.7 ± 11.8 | <0.001 |
| Diastolic blood pressure, mmHg | |||||||
| Early pregnancy | 67.9 ± 9.3 | 66.8 ± 9.2 | 67.2 ± 9.0 | 67.7 ± 9.2 | 68.6 ± 9.4 | 69.4 ± 9.4 | <0.001 |
| Mid pregnancy | 67.0 ± 9.2 | 66.2 ± 9.3 | 66.4 ± 8.6 | 66.6 ± 9.1 | 67.4 ± 9.5 | 68.5 ± 9.3 | <0.001 |
| Late pregnancy | 68.9 ± 9.2 | 67.7 ± 9.5 | 68.2 ± 8.7 | 68.6 ± 9.2 | 69.6 ± 9.2 | 70.3 ± 9.0 | <0.001 |
| Uterine artery resistance index | |||||||
| Mid pregnancy | 0.54 ± 0.09 | 0.54 ± 0.08 | 0.54 ± 0.09 | 0.54 ± 0.09 | 0.55 ± 0.09 | 0.53 ± 0.09 | 0.08 |
| Late pregnancy | 0.48 ± 0.08 | 0.49 ± 0.08 | 0.49 ± 0.08 | 0.48 ± 0.08 | 0.48 ± 0.08 | 0.48 ± 0.08 | 0.26 |
| Umbilical artery pulsatility index | |||||||
| Mid pregnancy | 1.20 ± 0.18 | 1.18 ± 0.18 | 1.20 ± 0.18 | 1.20 ± 0.18 | 1.21 ± 0.18 | 1.22 ± 0.18 | <0.05 |
| Late pregnancy | 0.98 ± 0.17 | 0.98 ± 0.17 | 0.98 ± 0.17 | 0.98 ± 0.17 | 0.98 ± 0.17 | 0.98 ± 0.17 | 0.94 |
| Bilateral uterine artery notching | 108 ± 1.8 | 19 ± 1.6 | 25 ± 2.1 | 22 ± 1.8 | 20 ± 1.7 | 22 ± 1.8 | 0.90 |
| Gestational hypertensive disorders | |||||||
| Preeclampsia, n (%) | 123 (2.1) | 20 (1.7) | 32 (2.7) | 25 (2.1) | 20 (1.7) | 26 (2.2) | 0.38 |
| Gestational hypertension, n (%) | 228 (3.8) | 26 (2.2) | 35 (2.9) | 44 (3.7) | 47 (3.9) | 76 (6.4) | <0.05 |
1
Values are shown as the mean ± SD, median [95% range], or count (%). CRP, C-reactive protein; TSAT, transferrin saturation.
2
Differences between characteristics in serum ferritin quintiles were tested with a 1-way ANOVA for continuous variables and χ2 test for categorical variables.
3
In the full study population, European ethnicity consisted of 52.5% Dutch and 8.5% other European ethnicities. Non-European ethnicity (39.0%) consisted of 8.5% Surinamese, 8.1% Turkish, 6.0% Moroccan, 4.2% Cape Verdian, 3.0% Indonesian, 2.9% Antillean, 2.7% Asian, 1.9% American, 1.7% African, and 0.1% Oceanian.