Objectives: 1,25 dihydroxyvitamin D [1,25(OH)2D] starts to rise from the first trimester of pregnancy and increases maternal intestinal calcium absorption. The preferred method in the diagnosis of Vitamin D deficiency is the measurement of 25 hydroxyvitamin D [25(OH)D]. However, fetal and placental structures produce 1,25(OH)2D and affect calcium metabolism during pregnancy. In this study, we aimed to evaluate 25(OH)D and 1,25(OH)2D levels in early pregnancy. Methods: Thirty-eight pregnant and 28 non-pregnant women were included in the study. Their 25(OH)D, 1,25(OH)2D, calcium, albumin, and parathormone levels were evaluated. Results: 25(OH)D levels were below 20 ng/mL in both groups, but lower in the pregnant group (mean 12.3 [±7.5] ng/ mL in pregnant, and 19.4 [±14.4] ng/mL in non-pregnant, p=0.017). 1,25(OH)2D levels were higher in the pregnant group (mean 105.9 [±29.2] pg/mL in pregnant, and 81.5 [±31.9] pg/mL in non-pregnant, p=0.003). Conclusion: 1,25(OH)2D plays a primary role in meeting the increased calcium need during pregnancy and provides a protective effect in terms of both fetal and maternal skeletal complications. The increase in 1,25(OH)?D starting from the first trimester is a pregnancy-specific mechanism in enhancing intestinal calcium absorption and providing the calcium requirement for the developing fetus. Thus, it may be useful to measure 1,25(OH)?D, in addition to 25(OH)D, when deciding on Vitamin D replacement in pregnant women of any trimester. Keywords: 1, 25 dihydroxy vitamin D, 25 hydroxyvitamin D, first trimester, pregnancy, Vitamin D
Corresponding Author: Melisa Sahin Tekin