Pregnancy and lactation are periods of high calcium demand for skeletal growth and maternal milk production. Approximately 25-30 g of calcium are transferred to the fetus during pregnancy, and breast-feeding mothers secrete 200-240 mg/day of calcium in breast milk every day. During pregnancy, major physiologic adaptations include increased both calcium intestinal absorption and rate of maternal bone turnover; during lactation, there is a contribution of renal calcium conservation, but temporary maternal bone demineralization is the main mechanism to meet calcium requirements. Data on bone mineral density assessed by dual energy x-ray absortiometry (DXA) are sparse mainly due to concern about potential risk of radiation exposure to the fetus. Other radiation-free techniques like quantitative ultrasound have been used to assess maternal bone mass changes during pregnancy. Maternal bone los...