During pregnancy, mineralization of the fetal skeleton creates a demand for approximately 30 g of calcium from maternal sources. We examined whether this fetal demand results in maternal femoral bone mineral loss. Femoral bone mineral density was measured twice by dual photon densitometry, once before conception and again within 15 days of parturition, in 32 white women aged 20-40 years. Femoral bone mineral density was also measured twice in 32 nonpregnant controls matched to the cases for weight, height, age, and parity. There was no significant mean bone mineral density loss in cases compared with controls (P>.63). Pregnant women with smaller body size, expressed as Quetelet index, were more likely to have femoral neck bone mass increase than their matched controls (P<.03). This study provides evidence that fetal demand for calcium has a minimal effect on bone. mineral density at parturition. Smaller women may experience a slight increase in femoral bone mineral density compared with controls. (Obstet Gynecol 77:841, 1991)