Yang Liu-Qing, Pian Jing
A significant U-shaped relationship was observed overall between abstinence duration and normal sperm morphology (quadratic term p = 0.002), with an inflection point at 4.62 days (nadir: 3.01% on Day 5). This relationship was significant in the ≤ 35-year group (p = 0.013, inflection 4.60 days) but not in the > 35-year group (p = 0.075). Age-abstinence interaction was non-significant (p = 0.878). No significant U-shaped or linear relationship was found between abstinence duration and sperm motility (progressive/total) in all groups.
BACKGROUND: Semen analysis is core to male fertility assessment, with abstinence duration being a key modifiable factor. Current evidence on its nonlinear effect on sperm morphology and age-related modifications remains scarce.
OBJECTIVES: To investigate the U-shaped effect of abstinence duration on normal sperm morphology rate and analyze age's modifying role, and further explore the differential effects of abstinence duration on various semen parameters.
MATERIALS AND METHODS: A retrospective analysis of 1262 males (2023-2024) with 2-7 days of abstinence was conducted. Quadratic regression models examined the abstinence-morphology relationship in the overall cohort and age-stratified groups (≤ 35 years, n = 996; > 35 years, n = 266), with U-curve inflection points calculated as -b1/(2b2). The effect of abstinence duration on sperm motility was also analyzed with the same model. The study was approved by the Ethics Committee (TAFY-LL-LW202601) and complied with the Helsinki Declaration.
RESULTS: A significant U-shaped relationship was observed overall between abstinence duration and normal sperm morphology (quadratic term p = 0.002), with an inflection point at 4.62 days (nadir: 3.01% on Day 5). This relationship was significant in the ≤ 35-year group (p = 0.013, inflection 4.60 days) but not in the > 35-year group (p = 0.075). Age-abstinence interaction was non-significant (p = 0.878). No significant U-shaped or linear relationship was found between abstinence duration and sperm motility (progressive/total) in all groups.
DISCUSSION AND CONCLUSION: Abstinence duration shows a U-shaped effect on normal sperm morphology rate in the overall population and in younger men (≤ 35 years). However, the age-abstinence interaction was not significant, indicating that the age-related difference should be interpreted with caution. Young men should avoid Day 5 of abstinence for accurate sperm morphology assessment, providing a comprehensive reference for personalized clinical semen analysis protocols.