Men’s sperm quality seems to deteriorate after the age of 35. The proportion of sperm carrying an X chromosome also seems to increase, meaning older dads are more likely to have daughters.

It has been controversial whether the quality and quantity of a man’s sperm deteriorates with age. “However, there is fairly convincing epidemiological evidence that older men do find it harder to conceive a child – regardless of female age – and as men get older their partners are at increased risk of miscarriage,” says Allan Pacey, a fertility specialist at the University of Sheffield, UK. There is also a slightly increased risk of older men fathering children with genetic disorders.

To investigate, Bronte Stone at Reproductive Technology Laboratories in Los Angeles and his colleagues analysed sperm samples from 5081 men aged between 16 and 72. They found a deterioration in sperm quality and quantity after age 35. Some previous studies had suggested that the decline doesn’t start until around five years later (Fertility and Sterility, doi.org/m85).

“Whether it’s 35 or 40, the message from this and other papers is that men should be aware of age-related changes in their reproductive system and if they wish to become fathers they shouldn’t leave it too late,” Pacey says.

The study also found a decrease in the ratio of Y to X-bearing sperm once men hit 55, though it is not clear why.

http://www.newscientist.com/article/mg21929275.500-mens-sperm-quality-decreases-at-age-35.html