Parity and Osteoporosis Risk
Much of the research reports an increase in bone density with increasing parity (the number of pregnancies a woman delivers past 28 weeks gestation.) The positive effect on bone density has been seen in both pre and postmenopausal women. Parity appears to have a protective effect against fracture, as well. In an arm of the Leisure World study, Paganini-Hill and others concluded that women with three or more children had a 30-40 percent reduction in hip fracture risk when compared to nulliparous women (those who have never given birth). The validity of studies that use nulliparous women as controls has been criticized, however. Many have suggested that nulliparous women may not be appropriate studies of parity since they have not demonstrated the ability to conceive and to support fetal growth and development. Such women may have a hormonal environment that impedes conception and negatively impacts bone density.