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.