Changes in bone mineral density and body composition during pregnancy and postpartum. A controlled cohort study.

In a controlled cohort study, bone mineral density (BMD) was measured in 153 women pre-pregnancy; during pregnancy; and 0.5, 4, 9, and 19 months postpartum. Seventy-five age-matched controls, without pregnancy plans, were followed in parallel. Pregnancy and breastfeeding cause a reversible bone loss, which, initially, is most pronounced at trabecular sites but also involves cortical sites during prolonged breastfeeding.
INTRODUCTION: Conflicting results have been reported on effects of pregnancy and breastfeeding on BMD and body composition (BC). In a controlled cohort study, we elucidate changes in BMD and BC during and following a pregnancy.
METHODS: We measured BMD and BC in 153 women planning pregnancy (n = 92 conceived), once in each trimester during pregnancy and 15, 129, and 280 days postpartum. Moreover, BMD was measured 19 months postpartum (n = 31). Seventy-five age-matched controls, without pregnancy plans, were followed in parallel.
RESULTS: Compared with controls, BMD decreased significantly during pregnancy by 1.8 ± 0.5% at the lumbar spine, 3.2 ± 0.5% at the total hip, 2.4 ± 0.3% at the whole body, and 4.2 ± 0.7% at the ultra distal forearm. Postpartum, BMD decreased further with an effect of breastfeeding. At 9 months postpartum, women who had breastfed for <9 months had a BMD similar to that of the controls, whereas BMD at the lumbar spine and hip was decreased in women who were still breastfeeding. During prolonged breastfeeding, BMD at sites which consist of mostly trabecular bone started to be regained, whereas BMD at sites rich in cortical bone decreased further. At 19 months postpartum, BMD did not differ from baseline at any site. During pregnancy, fat- and lean-tissue mass increased by 19 ± 22% and 5 ± 6% (p < 0.001), respectively. Postpartum, changes in fat mass differed according to breastfeeding status with a slower decline in women who continued breastfeeding. Calcium and vitamin D intake was not associated with BMD changes.
CONCLUSION: Pregnancy and breastfeeding cause a reversible bone loss. At 19 months postpartum, BMD has returned to pre-pregnancy level independently of breastfeeding length. Reversal of changes in fat mass depends on breastfeeding status.