Endocrine Abstracts

JOINT370

Objectives: During pregnancy and lactation, mobilisation of the maternal skeleton ensures sufficient calcium is available for fetal skeletal mineralisation. Maternal bone mineral density (BMD) typically reduces during these stages of the life course, with subsequent recovery after lactation ends. Recent trials have shown that pregnancy vitamin D supplementation can increase offspring BMD in childhood, but the effect on the maternal skeleton is poorly described. We previously demonstrated reduced maternal bone turnover (measured by urinary c-telopeptide) in pregnant women supplemented with cholecalciferol compared to placebo, but an effect on maternal BMD immediately after delivery was not detected in a subset of the women. Here, we assessed the effect of pregnancy vitamin D supplementation on the maternal skeleton in the medium term.

Materials and Methods: MAVIDOS was a randomised placebo-controlled trial of 1000 IU/day cholecalciferol from 14-17 weeks gestation until delivery. Participants were invited to have a Dual-Energy Xray absorptiometry (DXA) scan of the whole-body (analysed less head: WBLH), lumbar spine (LS) and left hip at 4 years after delivery. A subset of the women also had a DXA scan within 2 weeks of delivery. BMD at 4 years postpartum was compared between groups using linear regression in unadjusted and adjusted models (age, further pregnancy, duration of lactation, height, weight). β (95%CI) represents the effect of cholecalciferol compared to placebo. In women with DXA at both time points, the effect of cholecalciferol was assessed using mixed effects modelling to account for repeated measures.

Results: DXA imaging was performed on 443 participants (225 placebo, 218 cholecalciferol) at a median of 4. 1 years (IQR 4. 0, 4. 2) after delivery. Late pregnancy serum 25-hydroxyvitamin D was higher in the supplemented women (placebo 42. 0 nmol/l (SD 21. 5), cholecalciferol 70. 4 nmol/l (SD 19. 0), P < 0. 001). BMD measured 4 years after delivery did not differ between the two randomization groups in unadjusted or adjusted analyses (adjusted WBLH β=0. 000 g/cm² (0. 012, 0. 012), LS β=0. 009 g/cm² (-0. 010, 0. 027), total hip β=0. 004 g/cm² (-0. 014, 0. 022)). 223 women had DXA at birth and 4 years. BMD increased between the two scans in both groups (placebo WBLH 6. 3%, LS 1. 2%, hip 2. 2%; cholecalciferol WBLH 6. 2%, LS 1. 0%, hip 2. 4%, P < 0. 05 for all). However, the randomisation group had no effect on BMD (p>0. 05 for all).

Conclusions: Despite previously demonstrated increases in offspring BMD in childhood in the same trial, in this study, pregnancy supplementation with 1000 IU/day cholecalciferol did not benefit maternal BMD measured by DXA.