The goal of this observational study is to investigate the impact of underpants fit among Thai males attending the Infertility Clinic, whether alone or with their spouses. The main questions it aims to answer are:

• Assessing the effect of underpants fit on basic semen parameters and sperm DNA integrity.
• Determining the prevalence of preferred type of underpants worn by Thai males.

The participants will need to provide informed consent, complete a questionnaire consisting of 28 questions, and provide a semen sample.

This research aims to investigate the impact of underpants fit on basic semen parameters, with secondary objectives including an examination of its effect on sperm DNA integrity and an assessment of the prevalence of different underpants types among Thai male partners. The study will enroll approximately 120 Thai male partners, aged 20-55 years, attending the Reproductive Biology Unit (Infertility Clinic) at King Chulalongkorn Memorial Hospital in Bangkok, Thailand, either alone or with their spouses. Participants will be required to provide informed consent, complete a 28-question questionnaire, which should take no more than 10 minutes, and undergo semen analysis. The analysis will assess basic semen parameters and sperm DNA integrity, preferably after a 2-7 days abstinence period. The research will be conducted over a single day for each participant.

The data will be divided into two groups based on underpants fit: loosely fitted and tightly fitted. Statistical analysis will be conducted using STATA software version 18, employing regression analysis to assess the independent impact of underpants fit on semen quality. This analysis will control for potential confounding factors such as age, obesity, alcohol and caffeine consumption, cigarette smoking, physical activity, excessive heat exposure, recreational drug use, recent COVID-19 infection, duration of abstinence, previous children, and stress.

This study seeks to build on previous findings, address genital heat stress in Thai male partners, and potentially influence lifestyle changes to reduce male-factor infertility. Future research could explore additional factors such as underwear material and the type of trousers worn by men.

Inclusion Criteria:

• Male partner, Thai citizen
• Age 20 - 55 years
• Participants able and willing to fill in an informed consent form
• Participants capable of completing questionnaire form
• Semen sample collection after 2-7 days of abstinence
• Participants wearing specific type of underpants not less than 8 hours per day

Exclusion Criteria:

• Any congenital factor (e.g. cystic fibrosis, congenital absence of vas deferens, cryptorchidism)
• Any testicular disorder (e.g. varicocele, testicular torsion, testicular trauma)
• Any genital tract disorders/ infections (e.g. prostatitis, epididymitis, urogenital tract obstruction)
• Severe systemic disorder (e.g. liver cirrhosis, renal failure)
• Sexual dysfunction (erectile dysfunction)
• Exogenous factors (chemotherapy, medications, radiation)
• Any surgery comprising vascularization of testis
• Participants wearing both tight and loose-fitted underpants

Gender: Male Eligibility Criteria: Male individuals, aged 20-55 years, and citizens of Thailand.

The study aims to enroll approximately 120 participants, comprising Thai male partners who either alone or with spouses visit the Reproductive Biology Unit (Infertility Clinic) at King Chulalongkorn Memorial Hospital.