Association of hypertension with parity and with the interaction between parity and body mass index in rural Chinese women

A cross-sectional study was conducted; information for 9247 women living in rural China was collected by questionnaire interview and anthropometric and laboratory measurements during July to August 2013 and July to October 2014. Multiple logistic regression analysis was used to examine the association between parity and hypertension, estimating odds ratios and 95% confidence intervals (CIs). The biological interaction between parity and body mass index was estimated by the relative excess risk due to interaction, attributable proportion due to the interaction, and synergy index. In our study, the prevalence of multiparity and hypertension was 93.10% and 22.90% in premenopausal women and 98.04% and 51.06% in postmenopausal women, respectively. For premenopausal women, parity hypertension was not associated with hypertension. And for postmenopausal women, as compared with para 0-1 status, para 2, 3, 4, and ≥ 5 were positively associated with hypertension: adjusted odds ratios (95% CI) was 2.04 (1.24–3.38), 2.25 (1.32–3.82), 2.41 (1.34–4.36), and 2.10 (1.04–4.22), respectively. The interaction effect between multiparity and overweight/obesity on hypertension was additive (relative excess risk due to interaction [95% CI]: 1.59, 0.19–3.00; attributable proportion due to the interaction [95% CI]: 0.34, 0.02–0.67) only in postmenopausal women. Parity was independently related to hypertension, and the interaction effect between multiparity and overweight/obesity on hypertension was additive in rural postmenopausal women.