Effect of pregnancy on bone mineral density and biochemical markers of bone turnover in a patient with juvenile idiopathic osteoporosis

Juvenile idiopathic osteoporosis (JIO) is rare, presenting with vertebral fractures in the immediate prepubertal years; however, recovery is normally observed. We report the case of a 19-year-old pregnant woman previously diagnosed with JIO. She experienced three vertebral fractures in the third trimester of pregnancy. She delivered by caesarean section at 38 weeks gestation. Spinal bone mineral density decreased by 25%, hip bone mineral density by 10%, and forearm bone mineral density by 3% during pregnancy. Bone resorption markers, free pyridinoline and deoxypyridinoline (fPYD and fDPD), were elevated at baseline and markedly increased during pregnancy (fPYD/fDPD at 0, 10, 15, 20, and 28 weeks and immediately postpartum: 36.2/11.5, 52.9/15.8, 54.3/13.3, 51.1/13.3, 90/21.8, and 95.6/22.7 nmol/mmol creatinine, respectively) The bone formation marker, bone-specific alkaline phosphatase (BSAP), was within the reference range at baseline and increased in the third trimester. (BSAP at 0, 10, 15, 20, and 28 weeks and immediately postpartum: 20.5, 18.3, 17.7, 19.8, 26.9, and 30.0 U/Iiter, respectively). Parathyroid hormone (PTH) was measured by two methods to assess the possible effect of PTH fragments. PTH(1-84) (Roche) showed little change during the pregnancy, whereas the Nichols assay [(1-84) and(7-84) PTH fragment], revealed increases paralleling the changes in bone resorption. This young woman's bone turnover showed an exaggerated response to pregnancy, with bone resorption predominating over formation. PTH fragments may have partially mediated this effect.