Objective: The physiological importance of the C3 epimers of vitamin D (3-epi-25OHD2/3) is uncertain and there have been limited studies determining the levels of these epimers in human populations. The aims of the current study were (1) to determine 3-epi-25OHD2/3 levels throughout non-diabetic and T1DM pregnancy, (2) to examine the relationships between 25OHD and 3-epi-25OHD, (3) to assess the impact of maternal BMI on 3-epi-25OHD and examine associations with markers of glycaemic control.
Methodology: An observational study of 52 pregnant controls without diabetes and 65 pregnant women with T1DM in a university teaching hospital. 25OHD and 3-epi-25OHD were measured by liquid chromatography tandem mass spectrometry.
Results: 3-Epi-25OHD was found in 90.2% of control (median 0.9nmol/L; range 0.1-5.9nmol/L), and in 94.5% of T1DM, women (median 1.4nmol/L; range 0.1-10.5nmol/L). In both control and T1DM groups, maternal and cord 3-epi-25OHD correlated significantly with 25OHD. Seasonal variation in maternal 3-epi-25OHD levels was evident in both groups; Summer levels were significantly higher than all other seasons in the control group (p<0.001) and significantly higher than Spring (p=0.003) and Winter (p<0.001) in the T1DM group. In T1DM women HbA1c was significantly negatively correlated with 3-epi-25OHD at trimesters 1 and 2 (p=0.049; p=0.001) and with cord 3-epi-25OHD (p=0.012). Maternal BMI >30kg/m(2) had a significant negative impact on 3-epi-25OHD.
Conclusion: Maternal 3-epi-25OHD exhibits seasonal variation and, in common with cord 3-epi-25OHD, correlates with 25OHD throughout both non-diabetic and T1D pregnancy. In T1DM women 3-epi-25OHD is associated with a key marker of glycaemic control.
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