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Abstract: FR-PO278

Free 25-OH Vitamin D, but Not Total 25-OH Vitamin D, Is Correlated with Gestational Age and Calcium in Normal Human Pregnancy

Session Information

Category: Mineral Disease

  • 1202 Mineral Disease: Vitamin D, PTH, FGF-23


  • Hocher, Berthold, University of Potsdam, Potsdam, Germany
  • Tsuprykov, Oleg, Institute for Laboratory Medicine, IFLB, Berlin, Germany, Berlin, Germany
  • Buse, Claudia, Institute for Laboratory Medicine, IFLB, Berlin, Germany, Berlin, Germany
  • Skoblo, Roman, Institute for Laboratory Medicine, IFLB, Berlin, Germany, Berlin, Germany

Basic science as well as epidemiological studies showed that vitamin D is causally involved in the pathogenesis of pregnancy-related diseases such as gestational diabetes as well as pregnancy-related hypertensive disorders, short- and long-term outcomes of the offspring. To translate this knowledge to clinical practice, suitable tools to determine the vitamin D status during pregnancy are mandatory. Since 25-OH vitamin D (25-OHD) is mainly bound to vitamin D binding protein (VDBP) in the circulating blood and female sex steroids regulate hepatic VDBP synthesis, it is doubtful whether the determination of total vitamin D, as it is currently clinical practice, does adequately reflect the vitamin D status of an individual pregnant women.


We compared the correlations of total serum 25-OHD, free serum 25-OHD, and 1,25-(OH)2D in 475 healthy pregnant women with gestational age, calcium, phosphorus, bone alkaline phosphatase and PTH. Free 25-OHD was either measured directly using a novel assay system for direct measurements of free 25-OHD as well as calculated free 25-OHD based on measurements of VDBP, albumin and total 25(OH)D.


Correlation of serum vitamin D isoforms with gestational age and selected serum parameters is shown in the Table.


Calculated and measured free 25-OHD provide comparable data and correlate much better with components of the endocrine vitamin D system and targets of vitamin D induced gene expression. Free 25-OHD concentrations decrease slightly during healthy pregnancy, whereas 1,25-(OH)2D concentrations increases substantially. Given the impact of vitamin D on maternal and offspring’s health outcomes, an adequate monitoring of the vitamin D status during pregnancy might require measurements of both free 25-OHD and 1,25-(OH)2D at different time points of gestation.

ParameterTotal 25-OHDMeasured Free
Calculated Free 25-OHD1,25-(OH)2D
Gestational Agep=0.685, r=0.027p=0.002, r=-0.206p<0.001, r=-0.276p<0.001, r=0.627
Calciump=0.065, r=0.085p<0.001, r=0.161p<0.001, r=0.223p<0.001, r=-0.217
Phosphatep=0.023, r=0.104p=0.671, r=0.020p=0.616, r=0.023p=0.712, r=0.017
Parathyroid Hormonep<0.001, r=-0.306p<0.001, r=-0.239p<0.001, r=-0.271p<0.001, r=-0.186
Bone-Specific Alkaline Phosphatasep<0.001, r=-0.163p<0.001, r=-0.214p<0.001, r=-0.230p=0.012, r=0.108
Albuminp=0.184, r=-0.061p=0.007, r=0.123p<0.001, r=0.180p<0.001, r=-0.510
Low-Density Lipoproteinsp=0.301, r=0.048p=0.007, r=-0.125p=0.001, r=-0.155p<0.001, r=0.399
Vitamin B6p=0.156, r=0.067p=0.004, r=0.138p<0.001, r=0.192p<0.001, r=-0.190