Table 4

Biochemical measures for maternal baseline, maternal delivery, and cord blood specimens, by supplementation group
Biomarker (units) Placebo Vitamin D Group difference 1 Group-by-time effect2
(n = 80) (n = 80) Mean 95% CI Mean 95% CI
25(OH)D (nmol/L)
   Baseline3 44.0 ± 20.9 45.4 ± 18.4 1.4 [−4.8, 7.5]
   Delivery (n = 130)4 38.4 ± 18.1 134.4 ± 30.7 96.0*** [87.6, 104.8] 94.6*** [85.0, 104.1]
   Cord (n = 132)5 39.0 ± 18.7 102.8 ± 28.6 63.9*** [55.8, 72.0]
Calcium (mmol/L)
   Baseline 2.27 ± 0.09 2.25 ± 0.09 −0.02 [−0.04, 0.01]
   Delivery (n = 130) 2.31 ± 0.11 2.32 ± 0.10 0.02 [−0.02, 0.05] 0.03 [−0.01, 0.07]
Albumin-adjusted calcium (mmol/L)
   Baseline 2.36 ± 0.07 2.35 ± 0.07 −0.01 [−0.03, 0.01]
   Delivery (n = 130) 2.40 ± 0.08 2.43 ± 0.09 0.03* [0.00, 0.06] 0.04* [0.01, 0.07]
PTH (pmol/L)6
   Baseline 2.7 (0.3, 9.3) 2.9 (0.5, 9.4) 0.02 [−0.7, -0.2]
   Delivery (n = 129)7 3.9 (0.3, 20.5) 2.3 (0.3, 9.8) −0.51*** [−0.8, -0.3] −0.53*** [−0.8, -0.3]
Urinary calcium-creatinine ratio (mmol/mmol) 8
   Baseline 0.24 (0.0, 0.68) 0.22 (0.0, 0.88) −0.01 [−0.07, 0.05]
   2 weeks (n = 151)9 0.26 (0.0, 1.11) 0.26 (0.0, 1.25) 0.03 [−0.04, 0.10]
   Delivery (n = 125)10 0.13 (0.0, 1.26) 0.20 (0.0, 2.26) 0.04 [−0.05, 0.14] 0.07 [−0.03, 0.16]

1 Mean difference [95% CI] between the placebo and vitamin D group at a given time, by ordinary least square estimation.

2 Mean difference [95% CI] in the change for vitamin D versus placebo group (difference in the slope) using generalized estimation equations (GEE) to account for within-subject correlations.

3 Mean ± standard deviation (SD).

4 Delivery specimens were those collected within +/−1 day of delivery; n = 63 and n = 67 in the placebo and vitamin D groups, respectively;

5 Cord serum available for n = 67 in the placebo and n = 65 in the vitamin D group.

6 Median (range) summarize maternal PTH concentrations, due to right-skewed distributions. PTH concentrations were log-transformed to approximate normality for regression analyses. The results presented as group differences are log-transformed PTH concentrations.

7 PTH concentration at delivery available for n = 63 in placebo group and n = 66 in the vitamin D group.

8 Median (Range) summarize Ca: Cr ratios in the first two columns. Ca: Cr ratios were square root-transformed to approximate normality for regression analyses; thus, the regression coefficients and confidence bounds are presented on a square-root scale.

9 Two-week specimens were defined as those collected 14 +/−1 days after enrolment.

10 Delivery urine samples were taken day of delivery, +/−1 day, n = 60 and n = 65 in the placebo and vitamin D groups, respectively.

*p-value < 0.05; **p-value 0.01; ***p-value < 0.001.

Roth et al.

Roth et al. Nutrition Journal 2013 12:47   doi:10.1186/1475-2891-12-47

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