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 distal radius with dual-energy X-ray absorptiometry before pregnancy, immediately after delivery, 1 month after the resumption of menses and 1 year thereafter. Because of the small number of subjects, only individual changes in BMD that were greater than 2 radical2 times the short-term in vivo precision 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 healthy women. The duration of postpartum amenorrhea (PPA) and of lactation in our 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 could be seen. The magnitudes of reproduction-related BMD changes in general seemed not to differ substantially from about +/- 5% variability in BMD changes in healthy nonpregnant and nonlactating women. There was, however, some tendency toward systematic bone loss at the lumbar spine (about -3%) during pregnancy and at the femoral neck during PPA (about -5% as compared with prepregnancy data). Some individuals can yet show large, systematic bone losses comparable to 1 SD in magnitude. The site-specific reproduction-induced bone loss and consequent recovery are apparently multifactorial phenomena that may be related not only to duration and magnitude of lactation and/or duration of postpartum amenorrhea, but also to prevailing biomechanical and dietary factors, and other yet unknown individually modulated factors.