O29 Bone turnover in pregnancy, measured by urinary C-terminal telopeptide of type I collagen (CTX), is influenced by vitamin D supplementation and is associated with maternal bone health: findings from the MAVIDOS trial

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Background: the pattern of change in maternal bone turnover throughout pregnancy is poorly characterized.Objective: we investigated changes across pregnancy in a marker of maternal bone resorption, urinary C-terminal telopeptide of type I collagen (CTX), the influence of gestational vitamin D supplementation, and associations between CTX and maternal postnatal bone indices. Design: the Maternal Vitamin D Osteoporosis Study (MAVIDOS) is a randomized, double-blind, placebo-controlled trial of 1000 IU/day cholecalciferol vs placebo from 14 weeks’ gestation to birth. Maternal second void urinary α- and β-CTX were measured (Enzyme Linked Immunosorbent Assay, ELISA) at 14 and 34 weeks’ gestation; DXA was performed within 2 weeks post-partum. Mann-Whitney rank sum, Spearman's rank correlation and linear regression were used to compare median CTX values within and between groups from early to late pregnancy, and associations with maternal bone outcomes. Results: 372 women had CTX and 25(OH)-vitamin D measured in early and late pregnancy. CTX at 14 and 34 weeks’ gestation were correlated in both placebo (r = 0.31) and cholecalciferol (r = 0.45) groups (P Conclusions: maternal urinary CTX, a bone resorption marker, rises through pregnancy, though to a lesser degree with gestational cholecalciferol supplementation, and is inversely associated with maternal bone mass post-partum.