Relationship between parity and bone mass in postmenopausal women according to number of parities and age

To investigate the impact of multiple pregnancies on postmenopausal bone mineral density (BMD).

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, 4-7, and > 7 parity groups as well as in age groups of < 65 and 65 in age groups of < 65 and > or = 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.

A total of 264 women with mean age of 63 +/- 8.7 and mean menopausal duration of 15.8 +/- 10.2 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 4-7 (vs. < or = 3) increased BMD nonsignificantly, but > 7 significantly decreased LS-BMD and FN-BMD as compared with 0-7 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 (> or = 65 vs. < 65 years) by 1.3% (p = 0.77) and -10.1% (p = 0.009) as compared with 0-7 parity group by -9.5% (p = 0.001) and -15% (p = 0.0001), respectively.

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.