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Obstet Gynecol. 2017 Jul;130(1):171-180. doi: 10.1097/AOG.0000000000002096.

Associations of Parity, Breastfeeding, and Fractures in the Women's Health Observational Study.

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Department of Medicine, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, California; the Women's Health Initiative Clinical Coordinating Center and the Cancer Prevention Program, Fred Hutchinson Cancer Research Center, Seattle, Washington; the Department of Epidemiology, University of Pittsburgh, Pittsburgh, Pennsylvania; the Department of Medicine, Division of Preventive Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; the Department of Epidemiology and Prevention, Wake Forest School of Medicine, Winston-Salem, North Carolina; the Department of Preventive Medicine and Public Health, University of Kansas School of Medicine-Wichita, Wichita, Kansas; the Departments of Epidemiology and Pediatrics, University of Iowa, Iowa City, Iowa; and the Departments of Medicine and Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, California.



To examine associations of several aspects of parity and history of lactation with incident hip fractures and clinical fractures and, in a subset of women, with bone mineral density.


In this observational study, we analyzed data from 93,676 postmenopausal women participating in the Women's Health Initiative Observational Study and all bone density data from the subset of participants who underwent bone density testing at three clinical centers. At baseline, participants were aged 50-79 years. Using Cox proportional hazards regression analysis, we examined associations of fracture incidence and bone density with several aspects of parity (number of pregnancies, age at first pregnancy lasting 6 months or greater, and number of pregnancies lasting 6 months or greater) and breastfeeding (number of episodes of breastfeeding for at least 1 month, number of children breastfed, age when first breastfed, age when last breastfed, total number of months breastfed).


The mean baseline age (standard deviation) of participants was 64 (±7.4) years (mean follow-up 7.9 years). During follow-up, the incident rate of hip fracture was 1.27%. Ten percent of participants were nulligravid. In fully adjusted models, number of pregnancies, parity, age at first birth, number of children breastfed, age at first breastfeeding, age at last breastfeeding, and total duration of breastfeeding were not statistically significantly associated with hip fracture incidence. There were no consistent associations of parity or lactation characteristics with overall clinical fracture risk or bone density. However, compared with never breastfeeding, a history of breastfeeding for at least 1 month was associated with a decreased risk of hip fracture (yes compared with no, hazard ratio 0.84, 95% confidence interval 0.73-0.98).


Patterns of parity and history of lactation were largely unrelated to fracture risk or bone density.

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