Changes in bone mineral density during pregnancy and postpartum: Prospective data on five women

Areal bone mineral density (BMD, g/cm(2)) of five healthy women (aged 26-30 years) was measured at the lumbar spine, right femoral neck and dominant d istal radius with dual-energy X-ray absorptiometry before pregnancy, immedi ately after delivery, 1 month after the resumption of menses and 1 year the reafter. Because of the small number of subjects, only individual changes i n BMD that were greater than 2(root)2 times the short-term in vivo precisio n were considered as significant changes. To obtain a further perspective, the reproduction-related BMD changes were compared with twice the standard deviation (SD) of the BMD changes in healthy premenopausal women (about +/- 5%), and with the SD of the BMD in a cross-sectional sample of young health y women. The duration of postpartum amenorrhea (PPA) and of lactation in ou r subjects ranged from about 2 months to 1 year and from 5 months to almost 2 years, respectively, No clear association between PPA and lactation coul d be seen. The magnitudes of reproduction-related BMD changes in general se emed not to differ substantially from about +/-5% variability in BMD change s in healthy nonpregnant and nonlactating women. There was, however, some t endency toward systematic bone loss at the lumbar spine (about -3%) during pregnancy and at the femoral neck during PPA (about -5% as compared with pr epregnancy data). Some individuals can yet show large, systematic bone loss es comparable to 1 SD in magnitude. The site-specific reproduction-induced bone loss and consequent recovery are apparently multifactorial phenomena t hat may be related not only to duration and magnitude of lactation and/or d uration of postpartum amenorrhea, but also to prevailing biomechanical and dietary factors, and other yet unknown individually modulated factors.