Fig. 2.

Stratified multivariable analysis of the association between WHR and infertility according to baseline characteristics. Each stratification adjusts for all factors (age, ethnicity, educational level, marital status, family poverty income ratio, physical activity, dietary supplements taken, smoking status, alcohol drinking status, hypertension, diabetes, regular menstrual periods, and trouble sleeping) except for the stratification factor itself. The likelihood ratio test was used to examine interactions among subgroups and WHR and statistical significance was set at a two-tailed p value of <0.05. PIR, family poverty income ratio; WHR, waist-hip ratio.