An Australian research has shown that overweight men are less likely to father children.
While it has been known for some time that obesity reduces the chances of a female conceiving, this is understood to be the first study to show the effects of a male's weight.
The study, which involved more than 300 couples, showed that as a man's weight increased, his chances of fathering a child decreased.
"Clinical pregnancy rates were significantly reduced as paternal body mass index increased," stuff.co.nz quoted Dr Hassan Bakos, of the University of Adelaide, as saying.
"Clearly. . . lifestyle choices should not be confined to the female partner when a couple is striving to achieve their dream of having a healthy baby," Dr Bakos added.
Couples participating in the study were either undergoing IVF treatment or an alternative sperm injection procedure, and almost 80 per cent of the men involved were either overweight or obese.
Dr Bakos said that the man's weight was found to have no bearing on the earliest phases of the fertilised embryos that were produced.
"However, by day four or five of the embryo cell division - when paternal genetic influence comes into play - there was evidence of impaired development," he said.
"Current studies in our laboratory suggest that DNA damage and oxidative stress may be involved," he added.
IVF processes involve the selection of the most viable fertilised embryos for implantation in the womb.
Dr Michelle Lane, from the Adelaide IVF clinic, where the study was conducted, said it provided clear evidence of the vital role a man's weight played for fertility.
"A healthy weight for women undergoing assisted conception improves clinical pregnancy rates.
However, the effects of male obesity on pregnancy outcomes has until now not been so clear," said Dr Lane, scientific director at Repromed.
The research results are to be presented at the Annual Scientific Meeting of the Fertility Society of Australia, which gets under way in Perth next week.