Re-categorization of body mass index to achieve andrological predictive power: a study in more than 20 thousand patients

Abstract

Body mass index (BMI) increase has been frequently associated with disturbances in semen quality. Nevertheless, it isn’t well established from which BMI values these negative effects are significant. Furthermore, since BMI scale has been prepared in relation to cardiovascular risk, it is not necessarily applicable to reproductive function.

The objectives were to characterize semen quality according to BMI in 20565 patients from the “Laboratorio de Andrología y Reproducción de Córdoba” (11/2006 to 12/2017); to evaluate their risk of suffering semen pathologies, and to establish one or more reference values in BMI scale, from which the risk of suffering sperm alterations is statistically elevated.

After signing the informed consent, patients’ BMI and semen quality were evaluated. Data were analyzed by ANOVA, Chi-square and Generalized Linear Models. Reference values were calculated by Multivariate Conglomerate Analyses K-means. Finally, a table with expected values of abnormalities for each new group resulted from BMI re-categorization was built.

Morbidly-obese and/or underweight patients showed the highest decrease in semen quality (in parameters like sperm concentration, total sperm count, motility and morphology; p<0,05) and higher chances of suffering semen abnormalities (oligozoospermia: 23,2% y 30,3% vs 14,6% in morbidly-obese, underweight and normal weight respectively; teratozoospermia: 47,5% y 55,4% vs 41,7% respectively y asthenozoospermia: 49,8% vs 34,7% respectively; p<0,05). The smallest summatory in sperm abnormalities were found at BMI=27kg/m2. Four reference points were identified, re-categorizing BMI in groups according to the risk of suffering semen disturbances. From lowest to highest: group1=BMI between 20 and 32kg/m2; group2=BMI<20 and BMI>32 to 37kg/m2; group3=BMI>37 to 42kg/m2 and group4=BMI>42kg/m2.

In conclusion, having a BMI below 20 or above 32kg/m2 is detrimental for semen; these negative effects increase from BMI>37kg/m2 and even further, from BMI>42kg/m2. The BMI re-categorization carried out in this study has andrological predictive power.