TABLE 3.
Effects of gestational age and serum 25(OH)D concentration on serum 24,25-dihydroxyvitamin D in pregnant adolescents1
| Fixed effects | β ± SE | P value |
|---|---|---|
| Intercept | 1.51 ± 0.043 | <0.0001 |
| Gestational age,2 wk | 0.0130 ± 0.0022 | <0.0001 |
| Serum 25(OH)D,3 ng/mL | 0.0667 ± 0.0027 | <0.0001 |
| Gestational age × serum 25(OH)D4 | 0.000853 ± 0.00020 | <0.0001 |
1Values are fixed-effects estimates from a random coefficients model of serum 24,25-dihydroxyvitamin D concentration conducted using SAS PROC MIXED with an unstructured covariance matrix, n = 78 subjects, 201 observations. 25(OH)D, 25-hydroxyvitamin D.
2Gestational age is centered at mean 28.7 wk.
3Serum 25(OH)D is centered at mean 27.8 ng/mL.
4The gestational age coefficient 0.0130 is the slope of gestational age when serum 25(OH)D is centered at mean 27.8 ng/mL. The slope of gestational age is zero when 25(OH)D is 12.6 ng/mL: 0 = 27.8 – (0.0130 ÷ 0.000853) – X. Solve for X = 12.6 ng/mL. Below this 25(OH)D concentration, the slope of gestational age is negative.