動情激素(estrogen)缺乏與鈣質代謝異常爲骨質疏鬆症(osteoporosis)的主要因子。大部份的骨質疏鬆性骨折，發生在缺乏動情激素的停經後婦女。然而懷孕時，胎兒會從母體取走約25-30克的鈣去發展骨骼，且懷孕會伴隨動情激素的減少而使母體骨質大量流失。因此本研究的目的是在於評估停經後的婦女，比較生產胎數的多寡對停經後婦女的骨質密度(Bone Mineral Density； BMD)的影響。141位（年齡範圍50-85歲）皆已停經1年以上，並有生過2胎以上及授乳經驗的女性患者，以雙能X光骨質密度儀(Lunar DPX-L, Madison, WI)測量她們腰椎及股骨頸的BMD值。統計分析的方式是在3個不同年齡層中（50-59歲：60-69歲：70歲以上），以線性迴歸方式，分別觀察胎數（2胎；3胎；4胎；5胎以上）與BMD值的關係。50-59歲及60-69歲族群，其生產胎數與BMD值間爲一反比關係，也就是BMD值是隨著生產胎數的增加而下降的，但在60歲以上族群的研究，卻爲一正比關係。腰椎與股骨頸的BMD高峰值，均出現在50-59歲生產2胎的族群(1.124g/cm^2, p=0.001； 0.850g/cm^2, p=0.007)，而腰椎與股骨頸的最低值則出現在69歲以上且生產5胎以上的族群(0.847g/cm^2, p<0.05； 0.649/cm^2, p<0.05)，其中以50-59歲族群，生產5胎以上的腰椎及股骨頸BMD值，分別較生產2胎者低16%及6%最爲顯著。本研究顯示BMD隨著年齡及胎數的增加而下降的，尤其已停經未超過l0年以上的50-59歲族群最爲明顯。其主要原因爲懷孕期與授乳期皆會造成動情激素及鈣質的大量減少。

Estrogen deficient and calcium metabolism disorder have been proposed as a risk factor for the development of osteoporosis. Most osteoporotic fracture occurs in the group of postmenopausal women with low estrogen level. However, during pregnancy the fetus takes approximately 30 g of calcium from the mother for skeleton development. The associated insufficient estrogen during pregnancy may lead to bone mineral loss. The aim of tjis study was to evaluate the influence of multiple pregnancies on the bone mineral density (BMD) in the postmenopausal women. The study included 141 post-menopausal women (range 50~85 years) who had more than one year menopause history and at least two pregnancies and breastfeeding experience. Lumbar spine and femoral neck bone mineral density (BMD, g/cm^2) was measured using dual energy x-ray absorptiometry (Lunar DPX-L, Madison, WI). The subjects were divided into three age groups (range 50~59, range 60~69, over 69) and BMD data are adjusted for differences in the number of pregnancy (range 2~5). BMD decreased significantly with increasing the number of deliveries in the group of 50~69 years, but not so in the group of age over 69 years. Peak BMD of lumbar spine (1.124 g/cm^2, p=0.001) and hip (0.850 g/cm^2, p=0.007) occurred in the group of 50-59 years with two deliveries. In addition, lowest BMD of lumbar spine (0.847 g/cm^2, p<0.05) and hip (0.649 g/cm^2, p<0.05) was presented in the age over 69 with over 5 deliveries. BMD was significantly lower for lumbar spine (16%) and hip (6%) in women with age of 50-59 and with over 5 deliveries in comparison with women with two deliveries. These findings indicated that BMD were significantly decreased with increasing age and number of pregnancies. We concluded that pregnancies and lactation could be used as risk factors for future osteoporosis.