Recategorisation of body mass index to achieve andrological predictive power: a study in more than 20 000 patients.

The aim of this study was to recategorise body mass index (BMI) in order to classify patients according to their risk of semen abnormalities. Patients (n = 20 563) presenting at an andrology laboratory were classified into five groups according to BMI: underweight (BMI <20 kg m⁻²), normal weight (BMI 20–24.9 kg m⁻²), overweight (BMI 25–29.9 kg m⁻²), obese (BMI 30–39.9 kg m⁻²) and morbidly obese (BMI >40 kg m⁻²). Semen quality was evaluated to determine: (1) differences between groups using analysis of variance (ANOVA); (2) the chances of semen abnormalities (using generalised linear models, Chi-squared tests and odds ratios); (3) reference BMI values with andrological predictive power (multivariate conglomerate analyses and multivariate analysis of variance (MANOVA)); and (4) expected values of abnormalities for each new group resulting from BMI recategorisation. Morbidly obese and underweight patients exhibited the highest decrease in semen quality and had higher chances of semen abnormalities. The smallest number of sperm abnormalities was found at a BMI of 27 kg m⁻². Four reference values were identified, recategorising BMI into four groups according to their risk of semen abnormalities (from lowest to highest risk): Group1,BMI between 20 and 32 kg m⁻²; Group2, BMI <20 and BMI >32–37 kg m⁻²; Group3, BMI >37–42 kg m⁻²; and Group4, BMI >42 kg m⁻². A BMI <20 or >32 kg m⁻² is negatively associated with semen quality; these negative associations on semen quality increase from a BMI >37 kg m⁻² and increase even further for BMI >42 kg m⁻². The BMI recategorisation in this study has andrological predictive power. Body mass index (BMI) is associated with cardiovascular risk but not necessarily male fertility. So, the aim of this study was to establish, by studying >20 000 patients, one or more BMI reference values that may be used to classify men according to their chance of having semen abnormalities. This recategorisation showed that having a BMI <20 or >32 kg m⁻² is associated with a decrease in semen quality and that these negative associations are increased for BMI >37 kg m⁻² and are even further increased for BMI >42 kg m⁻². [ABSTRACT FROM AUTHOR]