Bone turnover and mineral metabolism in the last trimester of pregnancy: effect of multiple gestation

OBJECTIVE: To test the hypothesis that maternal bone turnover and mineral stress are greater in multiple pregnancy than in singleton pregnancy. METHODS: We measured serum markers of bone turnover and mineral stress in 17 multiple and 30 singleton pregnancies during the third trimester. RESULTS: Serum 25(OH) vitamin D, a marker of vitamin D intake, was higher (61 +/- 5 versus 39 +/- 2 ng/mL, P < .001), and 1,25(OH)2 vitamin D was lower (50 [95% confidence interval (CI) 24-102] versus 64 pg/mL [95% CI 30-135], P = .03) in multiple than in singleton pregnancy. Carboxyterminal telopeptide of type I collagen, a marker of bone resorption, increased with gestational duration and was higher in multiple gestation (5.8 [95% CI 3.3-10.1] versus 4.4 ng/mL [95% CI 2.5-7.8], P = .005). Carboxyl-terminal propeptide of type 1 procollagen, a marker of bone formation, increased with gestational duration and was not different between groups (110 inverted question mark95% CI 36-337] versus 99 ng/mL [95% CI 34-286], P = .5). Calcitonin increased with gestational duration and was not different between groups (7.0 [95% CI 3.7-13.0] versus 7.8 pg/mL [95% CI 4.0-15.4], P = .37). Parathyroid hormone was not different between groups and decreased with increasing maternal age. CONCLUSION: Bone turnover indices increased with gestational duration. The bone resorption index was greater in multiple than in singleton gestation. Serum 25(OH) vitamin D was greater and 1,25(OH)2 vitamin D was lower in multiple gestation, presumably because of greater consumption of vitamin D and minerals by women carrying more than one fetus.

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