Pregnancy-associated osteoporosis: does the skeleton recover?

Osteoporosis in pregnancy is a rare clinical problem of unknown cause. If the bone loss results from the pregnancy alone it should improve toward normal after delivery; in contrast, where bone density was low before pregnancy, due to some other secondary cause, significant postpartum improvement might not be expected. Thirteen women (age 23-37 years) with pregnancy-associated osteoporosis presenting with either pain in the back and vertebral collapse (8 subjects) or pain in the hip (5 subjects) had consecutive dual-energy X-ray absorptiometry measurements of bone mineral density (BMD) for up to 8 years after an affected pregnancy. The BMD results were expressed as a Z-score in relation to an age-matched mean. The mean initial (0-6 months postpartum) BMD was low in both groups and at both sites. In the back pain group the mean spine Z-score (Ll-L4) was -3.34 (range -2.25 to -4.66) and mean total hip Z-score was -2.41 (range -1.44 to -3.82). In the hip pain group the mean spine Z-score was -2.00 (range -1.48 to -2.65) and mean hip Z-score was -2.19 (range -1.12 to -3.26). Subsequent mean hip and spine BMD increased significantly toward the lower end of the normal range. We conclude that a reversible part of the bone loss is related to the pregnancy itself. A low BMD before pregnancy cannot be excluded. Knowledge that the bone density increases after an affected pregnancy, combined with the known rarity of recurrent symptoms in subsequent pregnancies, is important in prognosis.