Male fertility problems, testicular cancer and common genital disorders may all be linked to hormone levels early in pregnancy, suggests a new study on rats.
Researchers already knew that male hormones - or androgens - such as testosterone work during foetal development to programme the reproductive tract.
However, it had been believed that any problems with reproductive development only kick in during a later stage of pregnancy when there are low levels of these androgens.
These problems could include testes not descending properly into the scrotum (cryptorchidism) or the urinary tract opening in the wrong place on the penis (hypospadias).
Now, the new study by boffins at the Medical Research Council Human Reproductive Sciences Unit shows that the critical "window" that determines future reproductive health may, in humans, be at 8 to 12 weeks into the pregnancy.
"We know from other studies that androgens work during foetal development to programme the reproductive tract. But our assumption was that it would be much later in pregnancy," the BBC quoted Lead author Dr Michelle Welsh, as saying.
She added the anogenital measurement i.e. distance between the base of the penis and the anus could be an early warning system of future reproductive problems in boys.
"Say a clinician were to examine a 30-year-old man with testicular cancer - previously there would have been no way of knowing what hormones he was exposed to in the womb. We would suggest that this measurement, even at this later stage in life, could offer an indication of hormone exposure," she said.
"For example, the shorter the distance, the less confident we can be that hormones have acted correctly and at the right time."