Transient osteoporosis of the hip in pregnancy: natural history of changes in bone mineral density.

A 31-year-old white female developed severe bilateral hip pain during the third trimester of pregnancy that persisted after parturition. Laboratory abnormalities (elevated alkaline phosphatase and erythrocyte sedimentation rate) and radiographic changes (faint demineralization of the femur in the more symptomatic hip on plain films with evidence of bone marrow oedema and small joint effusions bilaterally on MRI) in the absence of other causes of focal osteoporosis were consistent with the diagnosis of transient osteoporosis of the hip in pregnancy. Although loss of bone mineral density (BMD) characterizes this syndrome, serial BMD measurements in symptomatic transient osteoporosis of the hip in pregnancy have not previously been reported. In the case reported here, serial bone density measurements were obtained over a 4-year period following the onset of symptoms. BMD in both femoral necks, which initially was approximately 20% lower than the average for age matched controls, increased markedly during the first year, plateaued during the following year, and then rapidly increased again following cessation of lactation. Unexpectedly, BMD in the lumbar spine, an asymptomatic site, was also markedly decreased at the time of presentation (31% lower than the mean of age-matched controls). Recovery of spinal density did not occur during the first year. However, spinal BMD did begin to increase during the second year and continued to rise after the cessation of lactation. In contrast to the marked reduction in bone density at these site of trabecular bone, cortical bone density in the forearm was normal. Possible aetiologies of pregnancy associated osteoporosis are discussed.