Scientists are warning men to freeze some of their sperm before having a vasectomy because the procedure may damage sperm.
According to fertility expert Professor Nares Sukcharoen, of the Chulalongkorn University in Bangkok, a vasectomy can be reversed and men have fathered children afterwards, but such men may have an increased risk of damaged sperm.
As many as 40,000 vasectomies are carried out in Britain each year, and around 2,500 men later want the surgery reversed often because they wish to have a family with a new partner.
Vasectomy is a quick and minor surgical procedure which is done under local anaesthetic and involves sealing the tubes, or vas deferens, that carry sperm.
As a rule it does not affect a man's sex drive or performance.
In reversal surgery the tubes are rejoined but the operation is not always successful.
Professor Sukcharoen and his team carried out a small study of men who had a vasectomy reversal and found that they had a 10 times higher number of chromosome abnormalities in their sperm than men who had not had the surgery.
The researchers tested 21 sperm samples from 18 men and found that 3.3% of their sperm had genetic defects, including abnormally high rates of chromosomal defects called sexual aneuploidies, where sperm had an extra X or Y chromosome which cause a number of medical conditions in children, such as Klinefelter syndrome, in which boys are born with an extra X chromosome and often develop abnormally proportioned bodies and experience learning difficulties.
Another rarer condition found called Triple X syndrome, affects around one in 2,000 girls, and is caused by sperm carrying two X chromosomes instead of the usual one.
It can lead to women developing symptoms including seizures and infertility.
Professor Sukchareon who led the study, says he believes a pressure build-up in the vas deferens disrupts the normal production of sperm in men who have had vasectomies and says the study shows that a vasectomy can cause abnormalities in sperm.
He says if a couple conceive naturally after the man has had a vasectomy reversal, the woman's body might select only the best sperm.
However if the sperm were used in artificial fertilisation, the genetic defects might be passed on to the child.
Sukcharoen says more research and larger studies are needed to confirm his results and to answer other questions regarding reversal surgery and the related problems.
The research was presented this week at a European Society of Human Reproduction and Embryology (ESHRE) meeting.