Socioeconomic disparities in the association of age at first live birth with incident stroke among Chinese parous women: A prospective cohort study

Stroke has become a significant public health issue in China. Although studies have shown that women's age at first live birth (AFLB) might be associated with incident stroke, there is limited evidence on this relationship among Chinese parous women. Likewise, the nature of this association across urban-rural socioeconomic status (SES) has yet to be explored. In this prospective study, we sought to investigate the associations of women's AFLB with the risk of incident stroke and its subtypes (ischaemic stroke, intracerebral haemorrhage, and subarachnoid haemorrhage) and to explore the differences of these associations as well as the population-level impacts across SES classes. We used data on 290 932 Chinese parous women from the China Kadoorie Biobank who were recruited in the baseline survey between 2004 and 2008 and followed up until 2015. We used latent class analysis to identify urban-rural SES classes and Cox proportional hazard regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for AFLB's association with incident stroke. We then calculated population attributable fraction (PAF) to demonstrate the population-level impact of later AFLB on stroke. Around 8.9% of parous women developed stroke after AFLB. Compared with women with AFLB