Adjusted HRs (with 95% CIs) of miscarriage associated with BMI categories. Hazard ratios were derived from the Cox proportional hazards regression model. The HR of BMI on the categorical scale was calculated as follows: HR = hazard rate [H(t)] of the different BMI categories / [H(t) BMI reference category (normal weight)]. An HR greater than 1 indicates a higher probability of miscarriage per week compared with the reference category. A, Main analysis for women with adjustment for participant’s age, ethnicity, educational level, smoking, alcohol consumption, parity, and history of miscarriage. The survival curve was derived from the unadjusted model. B, Main analysis for men with adjustment for participant’s age, ethnicity, educational level, smoking, and alcohol consumption. The survival curve was derived from the unadjusted model. Several sensitivity analyses were performed, excluding episodes with assisted reproductive technology (eTable 18 in Supplement 1), including only first episodes of participants (eTable 19 in Supplement 1), and including partner’s BMI as a covariate (eTable 20 in Supplement 1). NR indicates not reached.