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 mine ral stress are greater in multiple pregnancy than in singleton pregnan cy. Methods: We measured serum markers of bone turnover and mineral st ress in 17 multiple and 30 singleton pregnancies during the third trim ester. 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 (CD 24-102] versus 64 pg/mL [95% CI 30-135], P = .03) in multiple than in singleton pregnan cy. Carboxyterminal telopeptide of type I collagen, a marker of bone r esorption, increased with gestational duration and was higher in multi ple 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 mar ker of bone formation, increased with gestational duration and was not different between groups (110 [95% 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 r esorption index was greater in multiple than in singleton gestation. S erum 25(OH) vitamin D was greater and 1,25(OH)(2) vitamin D was lower in multiple gestation, presumably because of greater consumption of vi tamin D and minerals by women carrying more than one fetus.