Age
It is well researched that both female and male fertility declines with age – particularly for women as female fertility starts to decline after the age of 35.
The number of eggs decreases with age, and the older the female is, the remaining eggs are more likely to have abnormal chromosomes. The peak reproductive years for a female is between late teens and 30. Studies has shown the quality of sperm produced declines with age. Men older than 40 have fewer healthy sperm than men who are younger.