To estimate the prevalence of vitamin D inadequacy and to characterize the physiological changes in 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxivitamin D [1,25(OH) 2D] across healthy pregnancy.
A cohort of 229 apparently healthy pregnant women was followed between 5th-13th, 20th-26th and 30th-36th gestational weeks. The 25(OH)D (nmol/L) and 1,25(OH)2D (pmol/L) were measured by LC-MS/MS, method considered the gold standard. The vitamin D status in the first trimester was based on 25(OH)D categorized as inadequate (<75 nmol/L) and adequate (=75 nmol/L) according to the U.S. Endocrine Society. Statistical analyses included longitudinal linear mixed-effects models reporting regression coefficient (ß) and 95% confidence intervals
The mean age was 26.6 year and pre-pregnancy BMI = 25 kg/m2 was 40.2%. The prevalence of vitamin D inadequacy was high during the first trimester, second and third trimesters (70.4%, 41.0% and 33.9%, respectively). Women who started the study during winter presented a higher prevalence of 25(OH)D inadequacy (88.2%) compared to those who started in summer (54.8%) or autumn (59.6%). There was a mean increase in 25(OH)D (ß= 0.869; 95% CI: 0.723-1.014; P<0.001) and 1,25(OH)2D nmol/L (ß)= 3.878; 95% CI, 3.136-4.620; P<0.001) concentrations during pregnancy.
The prevalence of vitamin D inadequacy was high across pregnancy. A seasonal variation was observed. The concentrations of 25(OH)D and 1,25(OH)2D increased across trimesters.