Bone-mass peak in multiparity and reduced risk of bone-fractures in menopause

Objectives: Pregnancy has been proposed as a risk factor for the development of osteoporosis; however, the results are controversial. Women in Colombia are multiparous, and therefore they represent an ideal population for the investigation of the effect of parity on osteoporosis. Methods: The study included 1855 post-menopausal Hispanic women from Barranquilla, Colombia who were referred to our osteoporosis clinic for a routine evaluation of their bone mineral status. Bone mineral density (BMD, g/cm²) was measured using dual energy X-ray absorptiometry. Total body, femoral and lumbar areas were scanned. Results: BMD of total body, hip and legs (P < 0.0001), Ward's area (P < 0.002) and intertrochanteric area (P < 0.003) was high in women with at least one delivery in comparison with nulliparous women. Total mineral and calcium body contents were also high in women after second delivery. A history of fractures was found in 22.9% (n = 425) of the study women. The relative risk for bone-fractures was high (O.R. 0.41; P < 0.000002) in nulliparous women in comparison to multiparous women. In addition, osteopenia (O.R. 2.01; P = 0.008) and osteoporosis (O.R. 3.99; P = 0.0004) were most often present in nulliparous women in comparison to multiparous women. Conclusions: Pregnancies in this population appear to be a protective factor against development of osteoporosis. The increase in total mineral and calcium contents was related to the number of pregnancies, suggesting the existence of a bone mass peak during pregnancy.