April 16th, 2014

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Relationship Between Parity and Bone Mass in Postmenopausal Women According to Number of Parities and Age
Authors:  Behzad Heidari, M.D., Parnaz Heidari, Haj Ghorban Nourooddini, M.D., and Karim Ollah Hajian-Tilaki, Ph.D.
  OBJECTIVE: To investigate the impact of multiple pregnancies on postmenopausal bone mineral density (BMD).

STUDY DESIGN: BMD at the femoral neck (FN) and lumbar spine (LS) was measured by dual energy X-ray absorptiometry (DXA) method. Diagnosis of osteoporosis (OP) was confirmed by World Health Organization criteria. Women were stratified according to number of parity as <3, 47, and >7 parity groups as well as in age groups of <65 and ≥65 years. BMD values and frequency of OP were compared across the groups according to age. Multiple logistic regression analysis with calculation of adjusted odds ratio (OR) was used for association.

RESULTS: A total of 264 women with mean age of 638.7 and mean menopausal duration of 15.810.2 years were studied. LS-OP and FN-OP were observed in 28% and 58.3% of women, respectively. There were significant differences in BMD values across different parity groups at both sites of LS and FN (p=0.011 and p=0.036, respectively). Parity 47 (vs. ≤3) increased BMD nonsignificantly, but >7 significantly decreased LS-BMD and FN-BMD as compared with 07 parity (p=0.006 and p=0.009, respectively). Parity >7 increased the risk of LS-OP by OR=1.81 (95% CI 1.03 3.1, p=0.037) and FN-OP by OR=1.67 (95% CI 0.97 2.8, p=0.063). In addition, women with high parity had lower BMD decline at LS and FN by age (≥65 vs. <65 years) by 1.3% (p=0.77) and 10.1% (p=0.009) as compared with 07 parity group by 9.5% (p=0.001) and 15% (p=0.0001), respectively.

CONCLUSION: Parity >7 is associated with spinal trabecular bone loss in younger postmenopausal women as well as an osteoprotective effect against age-related bone loss, which counteracts the early negative effect. Therefore, parity should not be considered as a risk factor for postmenopausal osteoporosis.
Keywords:  bone density; bone loss, age-related; bone mineral density; osteoporosis; parity; spine
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