Plasma 3-Epi-25-Hydroxycholecalciferol Can Alter the Assessment of Vitamin D Status Using the Current Reference Ranges for Pregnant Women and Their Newborns

Background: Vitamin D is critical for healthy pregnancies and normal fetal development. It is important to accurately ascertain vitamin D status in mothers and their newborns to establish the optimal vitamin D concentration during pregnancy. There are many different metabolites and epimers of vitamin D in peripheral blood and controversy as to the importance of epimers in estimating vitamin D status in maternal and infant health. Objectives: We undertook this study to measure 25-hydroxyvitamin D metabolites and epimers and their relations in maternal and cord blood and to evaluate the impact of the inclusion of epimers on assessing vitamin D status. Methods: We performed a substudy in a longitudinal cohort of pregnant women and their infants in Alberta, Canada [APrON (Alberta Pregnancy Outcomes and Nutrition) Study]. Maternal and cord blood plasma collected at the time of newborn delivery was stored at –70C until testing and assayed for 25-hydroxyergocalciferol [25(OH)D2], 25hydroxycholecalciferol [25(OH)D3], and 3-epi-25-hydroxycholecalciferol [3-epi-25(OH)D3] by using LC–tandem mass spectrometry. The effect of 3-epi-25(OH)D3 on estimates of vitamin D adequacy was explored by using McNemars chisquare test at both recommended thresholds of 50 and 75 nmol/L. Results: Ninety-two pairs of maternal and cord blood samples were obtained. 3-Epi-25(OH)D3 was detected in all samples, comprising 6.0% and 7.8% of 25(OH)D3 in maternal and cord blood, respectively. Positive correlations were found between 25(OH)D3 and 3-epi-25(OH)D3 for both maternal and cord blood (maternal blood: r = 0.34, P = 0.01; cord blood: r = 0.44, P = 0.01). In addition, regression analysis showed a significant association between vitamin D supplementation and 3-epi-25(OH)D3 in maternal and cord blood (b: 0.423; 95% CI: 0.173, 0.672). When 3-epi-25(OH)D3 was not included in plasma vitamin D estimations, 38% of women and 80% of neonates were classified as having an insufficient concentration (