Infertility in men may be determined before they are born, between eight and twelve weeks into pregnancy.
A University study has identified a time window between eight and 12 weeks of fetal development during which reproductive problems, including low sperm count, are determined.
Researchers at the Medical Research Council (MRC) Human Reproductive Sciences Unit, at the University, looked at the development of testes in rats.
They equated their findings to the equivalent period of development in humans.
By blocking the action of androgens, which include hormones such as testosterone, they were able to identify which period in development is significant for fertility in later life.
Researchers found that the same time window is significant in determining whether a baby will be born with conditions including cryptorchidism, when the testes fail to drop into the scrotum.
Cryptorchidism is the most common birth defect and is a risk factor for developing testicular cancer as a young man.
What is interesting is that the crucial time in fetal development is some time before the reproductive organs and the testes fully develop. What we need to find out now is why things go wrong, which could for instance be linked to the age, diet or lifestyle of the mother, and eventually how to prevent problems from occurring.
The findings were presented at the Simpson Symposium, named after Edinburgh professor James Simpson, who discovered chloroform.
It is run by the Centre for Reproductive Biology, a collaboration between the University of Edinburgh and the Medical Research Council.