Bone density changes during pregnancy and lactation in active women: a longitudinal study.

Six healthy active women, aged 28-34, had bone mineral density (BMD) measured (DPA & SPA) at seven sites prior to pregnancy, within 6 weeks of parturition, and after 6 months of lactation. Twenty-five nonpregnant women of the same age, height, weight, activity level and calcium intake were tested during the same period. Average calcium intake during pregnancy was 1526 mg/day; during lactation, 1622 mg/day. The nonpregnant women averaged 1756 mg/day. BMD decreased in the femoral neck (P less than or equal to 0.05) and radial shaft (P less than or equal to 0.05) during pregnancy but increased in the tibia (P less than or equal to 0.05). A 3.3% decrease in lumbar BMD during pregnancy returned to pre-pregnancy values during lactation. Bone loss at the femoral neck continued during lactation (P less than or equal to 0.05). Changes in BMD during pregnancy and lactation may represent changes in mechanical stress as a result of weight gain, changes in posture and/or activity, or some other factor specific to this population of active women.