Lumbar bone mineral density changes during pregnancy and lactation

Objective: To elucidate the change of bone metabolism in the lumbar trabecular and its relationship with serum hormonal changes in pregnancy and lactation. Study design: In a cross-sectional study, we measured the bone mineral density (BMD) of 2-4 lumbar vertebrae of 571 puerperae at days 3-5 postpartum and 341 healthy, non-pregnant women (control subjects) of approximately the same age by dual energy X-ray absorptiometry. In a longitudinal study, we also measured the BMD of 111 puerperae at 3 and 6 months after delivery. Results: The mean BMD at days 3-5 postpartum was significantly lower than that of the control (1.013 +/- 0.005 vs. 1.032 +/- 0.006 g/cm(2), P = 0.019). The lactating group showed BMD decrement to 95.1 +/- 0.5% (n = 69) and 94.1 +/- 0.7% (n = 61) at 3 and 6 months postpartum, respectively, compared with days 3-5 postpartum, and the amenorrhea group showed the same tendency. The non-lactating group and resumption of menses group did not show a BMD decrement postpartum. In the lactating group, serum estradiol was significantly lower than in the non-lactating group at 3 months postpartum, serum prolactin and bone alkaline phosphatase levels were higher than in the non-lactating group at 3 and 6 months postpartum. Conclusions: Pregnancy may cause a decrease of lumbar BMD, and the lactation and amenorrhea also cause a decrease of BMD. In addition to lactation status, the ovarian dysfunction is one of the factors in bone loss during lactation. (C) 1998 International Federation of Gynecology and Obstetrics.