Fertility decreases progressively with age in adult men. In older men, progressive testicular tissue atrophy, decreased daily sperm production, morphological changes in testicular reproductive tissues (e.g., increased atypical spermatogonia and abnormal spermatocytes, increased interstitial fibrosis of the varicoceles and increased desquamation of immature germ cells) and increased cellular mutations or heteroploidy may occur, resulting in decreased sperm quality (especially motility), decreased conception rates, increased abortion rates, and increased autosomal regions in the offspring. (i.e., Apert syndrome, chondrodysplasia, Marfan syndrome, Wardenburg disease, etc.) and increased fetal mortality. For sperm function, there were no significant differences between older and younger men, except for a slight decrease in sperm motility in the older male group, which was almost close to normal levels according to WHO standards. Cytogenetic analysis of semen specimens from sperm donors showed an increase in the number and structural aberrations of sperm chromatin in men aged 59-74 years compared to men in the 23-29 age group. These data suggest that paternal age may influence sperm chromatin structural aberrations. The California Study 5000 women showed that the probability of first early spontaneous abortion and second early spontaneous abortion increased when paternal age was 35 years or older. Another study noted that the increased risk of miscarriage depended on the age of both parents. All of the above reports were for men in their reproductive years, with some reported at ages younger than 35 years and most reported at ages older than 40 years or older than 50 years. Some studies suggest that the risk of miscarriage is increasing in men aged 40 years and older, especially when the mother is 35 years or older. A Danish study showed that paternal age over 50 years affected early fetal mortality two times more than paternal age was 45 years alone. The mechanism is currently unknown and these results may be due to increased sperm aneuploidy or sperm DAN quality.