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

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.

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/cm(2)) was measured using dual energy X-ray absorptiometry. Total body, femoral and lumbar areas were scanned.

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.

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.