Basic characteristics of participants according to the number of live births
Basic characteristics of participants according to the number of live births are shown in Table 1. Compared with participants with one live births, both participants with zero and five or more children were more likely to be non-white with higher levels of Townsend deprivation index, and a higher percentage of asthma but a lower percentage of use of oral contraceptive pills. Meanwhile, childless participants were more likely to have a higher levels of education, and lower levels of BMI and moderrate activity time, and a lower percentage of current smoking rate but a higher percentage drinking rate; as well as a lower prevalence of diabetes, hypertension, emphysema and chronic bronchitis, and history of stillbirth, spontaneous miscarriage or termination. Reversely, participants with five or more children were more likely to have a lower level of education, and higher levels of BMI and moderrate activity time, and a higher percentage of current smoking rate but a lower percentage drinking rate, as well as higher prevalences of diabetes, hypertension, asthma, emphysema and chronic bronchitis, and history of stillbirth, spontaneous miscarriage or termination, comparied with correspondings in women without child. The age at menarche, age at menopause (last menstrual period), and the length of menstrual cycle are relatively average in each group, which are nearly 13 years old, 50 years old, and 27 days, respectively.