The influence of fit of underpants worn on semen quality

Background: Infertility in general has seen an upward trend in recent period. Male infertility has an estimated increase rate of 0.291% per year since 1990. Several factors have been studied as a cause of male infertility including idiopathic factors. One of the idiopathic factors in concern is clothing, which may increase intra-scrotal temperature. The genital heat stress has been reported to influence semen quality. Based on this factor, the previous studies done to discover association between type of underwear and semen quality have shown varying results that cannot be generalized to over-all population. This study aimed to assess the influence of fit of underpants worn by Thai male partners on semen quality in a single Infertility Center and discern proportion of Thai male partners wearing different type of underpants. Method: This cross-sectional study included 116 Thai male partners, aged 20-55 years, from the Reproductive Biology Unit (Infertility Clinic) at King Chulalongkorn Memorial Hospital in Bangkok, Thailand. Participants completed a 28-questionnaire form and provided semen samples for basic semen parameter assessment and sperm DNA integrity evaluation. Statistical analysis was conducted using STATA version 18, with linear and logistic regression analyses performed to control for confounding factors. Results: In our study, 93.1% of participants preferred tight underpants during the day, while 74.14% opted for boxers or none at night. Both univariate and multivariate regression analyses found significant associations: higher semen volume with loose-fitted underpants worn day and night (univariate p=0.006, 95% CI 0.352-2.036; multivariate p=0.004, 95% CI 0.406-2.057) and higher normal sperm morphology with tight-fitted underpants worn day and night (p=0.031 for both analyses; univariate 95% CI 0.046-0.952; multivariate 95% CI 0.044-0.937). These consistent findings suggest an association between the fit of underpants worn and semen quality.