Influence of number of pregnancies on bone mineral density in postmenopausal women of different age groups.

As data on the relationship between parity and bone mineral density often seem to be controversial, ultimately, a comprehensive research study was thought to be necessary. This study focused on examining the influence of the number of pregnancies on bone mineral density and investigating the relationship between pregnancy and bone mineral density at four sites in postmenopausal women of different age groups. A total of 509 postmenopausal women, varying from 45 to 86 years of age (mean age of 60.85 +/- 7.53 years) were considered for the study. A standardized interview was employed to obtain information on demographics, lifestyle, and, reproductive and menstrual histories. Patients were separated into four groups according to the number of pregnancies, i.e., nulliparae (52 patients), one to two parity (66 patients), three to five parity (178 patients), and more than five parity (213 patients). The patients were further classified into two age groups, 40-59 years (233 patients) and 60-80 years (276 patients), respectively. The number of pregnancies was found to range from 0 to 17 (with an overall mean of 5.42 +/- 3.68), with 4.29 +/- 2.74 (range, 0-16) accounting for live births, while 1.02 +/- 1.53 (range, 0-14) were abortions. There were no significant differences among the groups with respect to parameters such as, age, body mass index (BMI), age at menarche, age at menopause, and years since menopause (P > 0.05) in all of the 509 women and in the 40- to 59- and 60- to 80-year groups. When all the patients were considered, the bone mineral density (BMD) values of the spine and the trochanter for the more-than-five-parity group, were found to be significantly lower than those of the other groups (P < 0.05), while the BMD values of the spine and the femur (neck, trochanter) appeared to decrease with increasing parity. In the 40- to 59-year group, the BMD of the spine in both the nulliparae and one-to-two-parity groups was significantly higher than that of the more-than-five-parity group (P < 0.05). No significant differences were found among the groups with respect to the BMD values at any femur sites. The nulliparae patients in the 60- to 80-year group exhibited significantly higher trochanter and Ward's BMD values than those of the more-than-five-parity group (P < 0.05), whereas in the one-to-two-parity group, spine BMD values appeared to be significantly higher than those of the more-than-five-parity group (p < 0.05). Significant correlations were found between the number of pregnancies and BMD values for the spine (r = -0.23; P < 0.01), trochanter (r = -0.16; P < 0.01), and Ward's triangle (r = -0.14; P < 0.05), with no significant correlation for femur neck BMD (r = -0.08; P > 0.05) values. In conclusion, the present study suggests that the number of pregnancies has an effect on the BMD values and that this situation shows a variation in different age groups. In addition, our study indicates that there is a significant correlation between the number of pregnancies and the spine, trochanter, and Ward's triangle BMD, but there is no correlation for the femur neck BMD.