|Authors||Cunha Figueiredo, A.C., Cocate, P.G., Adegboye, A.R., Franco-Sena, A.B., Farias, D.R., Trindade de Castro, M.B., Brito, A., Allen, L.H., Mokhtar, R.R., Holick, M.F. and Kac, G.|
Purpose. To characterize the physiological changes in 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxivitamin
D [1,25(OH)2D] throughout pregnancy. Methods. Prospective cohort of 229 apparently healthy pregnant women followed at 5th-13th, 20th-26th and 30th-36th gestational weeks. 25(OH)D and 1,25(OH)2D concentrations were measured by LC-MS/MS. Statistical analyses included longitudinal linear mixed-effects models adjusted for parity, season, education, self-reported skin color and pre-pregnancy BMI. Vitamin D status was defined based on 25(OH)D concentrations according to the Endocrine Society Practice Guideline and Institute of Medicine (IOM) for adults. Results. The prevalence of 25(OH)D <75 nmol/L was 70.4%, 41.0% and 33.9%; the prevalence of 25(OH)D<50 nmol/L was 16.1%, 11.2% and 10.2%; and the prevalence of 25(OH)D <30 nmol/L was 2%, 0% and 0.6%, at the first, second and third trimester, respectively. Unadjusted analysis showed an increase in 25(OH)D (β=0.869;95%CI, 0.723-1.014; P<0.001) and 1,25(OH)2D (β=3.878; 95%CI, 3.136-4.620; P<0.001) throughout pregnancy.
Multiple adjusted analyses showed that women who started the study in winter (P<0.001), spring (P<0.001) or
autumn (P=0.028) presented a longitudinal increase in 25(OH)D concentrations, while women that started during
summer did not. Increase of 1,25(OH)2D concentrations over time in women with insufficient vitamin D (50-75
nmol/L) at baseline was higher compared to women with sufficient vitamin D (≥75 nmol/L) (P=0.006). Conclusions.
The prevalence of vitamin D inadequacy varied significantly according to the adopted criteria. There was a seasonal variation of 25(OH)D during pregnancy. The women with insufficient vitamin D status present greater longitudinal increases in the concentrations of 1,25(OH)2D in comparison to women with sufficiency.