Nulliparity and Fracture Risk in Older Women: The Study of Osteoporotic Fractures

Authors

  • Teresa A Hillier MD, MS,

    Corresponding author
    1. Center for Health Research, Kaiser Permanente Northwest/Hawaii, Portland, Oregon, USA
    • Center for Health Research Kaiser Permanente Northwest/Hawaii 3800 North Interstate Avenue Portland, OR 97227-1098, USA
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  • Joanne H Rizzo,

    1. Center for Health Research, Kaiser Permanente Northwest/Hawaii, Portland, Oregon, USA
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  • Kathryn L Pedula,

    1. Center for Health Research, Kaiser Permanente Northwest/Hawaii, Portland, Oregon, USA
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  • Katie L Stone,

    1. Department of Medicine, University of California San Francisco, San Francisco, California, USA
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  • Jane A Cauley,

    1. Department of Epidemiology, School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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    • Drs Bauer and Cauley have served as consultants for Pfizer and Astro Zeneca. All other authors have no conflict of interest.

  • Doug C Bauer,

    1. Department of Medicine, University of California San Francisco, San Francisco, California, USA
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    • Drs Bauer and Cauley have served as consultants for Pfizer and Astro Zeneca. All other authors have no conflict of interest.

  • Steven R Cummings

    1. Department of Medicine, University of California San Francisco, San Francisco, California, USA
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  • Presented in part at the 23rd Annual Meeting of the American Society for Bone and Mineral Research in Phoenix, AZ, October 12-16, 2001.

Abstract

Whether nulliparity increases fracture risk is unclear from prior studies, which are limited by small samples or lack of measured bone mineral density. No study has evaluated whether the effect of parity differs by skeletal site. We prospectively analyzed the relationship of parity to the risk of incident nontraumatic hip, spine, and wrist fractures in 9704 women aged 65 years or older participating in the Study of Osteoporotic Fractures to determine if parity reduces postmenopausal fracture risk, and if so, if this risk reduction is (1) greater at weight-bearing skeletal sites and (2) independent of bone mineral density. Parity was ascertained by self-report. Incident hip and wrist fractures were determined by physician adjudication of radiology reports (mean follow-up, 9.8 years) and spine fractures by morphometric criteria on serial radiographs. The relationship of parity to hip and wrist fracture was assessed by proportional hazards models. Spine fracture risk was evaluated by logistic regression. Compared with parous women, nulliparous women (n = 1835, 19%) had an increased risk of hip and spine, but not wrist, fractures. In multivariate models, parity remained a significant predictor only for hip fracture. Nulliparous women had a 44% increased risk of hip fractures independent of hip bone mineral density (hazards ratio, 1.44; 95% CI, 1.17-1.78). Among parous women, each additional birth reduced hip fracture risk by 9% (p = 0.03). Additionally, there were no differences in mean total hip, spine, or radial bone mineral density values between nulliparous and parous women after multivariate adjustment. In conclusion, childbearing reduces hip fracture risk by means that may be independent of hip bone mineral density.

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