TABLE 2.
Plasma 25-hydroxyvitamin D concentration according to time point and maternal socio-demographic and pregnancy characteristics
| Mixed model P values | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Variable | n | Trimester 1 11.5 ± 0.04 weeks GA | n | Trimester 3 33.1 ± 0.04 weeks GA | n | Delivery 39.3 ± 0.04 weeks GA | Overall mean | Variable | Interaction with time |
| Time, visit | 1905 | 69.8 ± 0.51 | 1649 | 78.6 ± 0.71 | 1543 | 75.7 ± 0.71 | — | <0.0001 | |
| Age, years | — | — | — | — | — | — | — | <0.0034 | 0.39 |
| <30 | 577 | 66.9 ± 0.9 | 504 | 76.0 ± 1.2 | 467 | 74.1 ± 1.2 | 72.0 ± 0.61 | ||
| 30–34 | 677 | 70.9 ± 0.8 | 586 | 80.1 ± 1.1 | 557 | 76.6 ± 1.1 | 75.6 ± 0.6 | ||
| ≥35 | 651 | 71.2 ± 0.8 | 559 | 79.3 ± 1.1 | 519 | 76.1 ± 1.1 | 75.3 ± 0.6 | ||
| Education | — | — | — | — | — | — | — | <0.0001 | 0.67 |
| ≤High school | 174 | 61.3 ± 1.7 | 139 | 69.2 ± 2.2 | 131 | 69.8 ± 2.2 | 66.3 ± 1.21 | ||
| College/bachelors | 1243 | 70.2 ± 0.6 | 1072 | 79.0 ± 0.8 | 1014 | 75.4 ± 0.8 | 74.6 ± 0.4 | ||
| Graduate degree | 488 | 71.7 ± 0.9 | 438 | 80.4 ± 1.4 | 398 | 78.3 ± 1.4 | 76.6 ± 0.7 | ||
| Household income | — | — | — | — | — | — | — | <0.0001 | 0.22 |
| ≤70,000 CAD | 555 | 65.1 ± 0.9 | 475 | 75.0 ± 1.2 | 455 | 72.8 ± 1.2 | 70.6 ± 0.6 | ||
| >70,000 CAD | 1258 | 72.2 ± 0.6 | 1104 | 80.7 ± 0.8 | 1022 | 77.5 ± 0.8 | 76.6 ± 0.41 | ||
| Not reported/known | 92 | 64.4 ± 2.5 | 70 | 69.1 ± 2.6 | 66 | 68.1 ± 3.1 | 66.9 ± 1.6 | ||
| Marital status2 | — | — | — | — | — | — | — | 0.0003 | 0.84 |
| Married/partner | 1812 | 70.1 ± 0.5 | 1575 | 78.9 ± 0.7 | 1470 | 76.1 ± 0.7 | 74.8 ± 0.4 | ||
| Other | 93 | 62.6 ± 2.3 | 74 | 70.8 ± 3.0 | 73 | 66.9 ± 3.3 | 66.4 ± 1.61 | ||
| Pre-pregnancy BMI, kg/m2 | — | — | — | — | — | — | — | <0.0001 | 0.30 |
| Underweight (<18.5) | 51 | 71.7 ± 2.9 | 41 | 82.7 ± 3.1 | 39 | 82.3 ± 3.2 | 78.3 ± 1.8 | ||
| Healthy (18.5–24.9) | 1063 | 72.2 ± 0.6 | 937 | 80.7 ± 0.9 | 864 | 77.7 ± 0.9 | 76.7 ± 0.5 | ||
| Overweight (25.0–29.9) | 386 | 68.9 ± 1.0 | 323 | 76.6 ± 1.4 | 313 | 75.5 ± 1.5 | 73.4 ± 0.8 | ||
| Obese (≥30.0) | 265 | 62.2 ± 1.3 | 228 | 73.1 ± 1.6 | 215 | 69.8 ± 1.7 | 68.0 ± 0.94 | ||
| Not known/available | 140 | 67.1 ± 1.7 | 120 | 75.6 ± 2.8 | 112 | 70.1 ± 2.8 | 70.8 ± 1.45 | ||
| Parity | — | — | — | — | — | — | — | 0.0324 | 0.0007 |
| 0 | 837 | 69.7 ± 0.7 | 740 | 80.8 ± 1.0 | 689 | 77.2 ± 1.05 | 75.6 ± 0.5 | ||
| 1 | 768 | 70.3 ± 0.7 | 656 | 77.4 ± 1.0 | 616 | 74.4 ± 1.06 | 73.8 ± 0.5 | ||
| 2+ | 300 | 68.7 ± 1.3 | 253 | 74.9 ± 1.77 | 238 | 74.5 ± 1.78 | 72.4 ± 0.9 | ||
| Smoking3 | — | — | — | — | — | — | — | <0.0111 | 0.28 |
| Never | 1156 | 70.1 ± 0.6 | 1021 | 79.0 ± 0.8 | 956 | 76.2 ± 0.9 | 74.9 ± 0.4 | ||
| Former/quit in pregnancy | 634 | 70.7 ± 0.8 | 545 | 78.9 ± 1.1 | 499 | 75.3 ± 1.2 | 74.7 ± 0.6 | ||
| Current | 115 | 61.6 ± 1.8 | 83 | 71.2 ± 2.7 | 88 | 72.0 ± 2.9 | 67.6 ± 1.41 | ||
| Multivitamin first trimester3 | — | — | — | — | — | — | — | <0.0001 | 0.30 |
| Yes | 1661 | 71.1 ± 0.5 | 1445 | 79.8 ± 0.7 | 1347 | 76.7 ± 0.7 | 75.6 ± 0.41 | ||
| No | 244 | 60.6 ± 1.5 | 204 | 69.5 ± 1.9 | 196 | 68.6 ± 2.1 | 65.9 ± 1.1 | ||
Data are n, mean ± SEM (nmol/L). Each model included the respective maternal characteristic as a fixed effect and time as a fixed repeated measure; recruitment center was a random effect. Differences among groups were tested using Tukey post hoc tests, with Tukey-Kramer adjustment for multiple comparisons. Abbreviations: CAD, Canadian dollars; GA, gestational age.
Main effects P < 0.05 compared with other group(s) for each variable (time, or maternal characteristic).
Marital status combined for married or with the same partner for over a year. Any other status includes single, divorced, separated, and other.
Supplement use and smoking history over previous 3 months were surveyed at the first trimester visit.
Interaction effect P < 0.05: different from underweight, healthy, and overweight.
Interaction effect P < 0.05: different from healthy.
Interaction effect P < 0.05: all pairwise differences within row.
Parity 2+ group lower than primiparous group.
Values increase from trimester 1 to 3, then stabilize.