A new study has found that women who smoke during pregnancy or breast feeding may harm the fertility of their sons.
While it was known that smoking during pregnancy could have a number of harmful effects on the developing foetus, the study, led by the researchers of University of Newcastle, is the first comprehensive animal model to show the mechanism by which smoking can affect the fertility of male offspring.
The team developed a machine that drew smoke into a nose piece; 27 female mice were placed in the machine with their noses introduced into the nose piece and they inhaled the smoke into their lungs in exactly the same way as a human would when smoking a cigarette. The amount of smoke inhaled represented the equivalent of a pack of 24 cigarettes a day in humans. Another 27 mice were exposed to normal air. After six weeks all the mice were placed with males to produce litters.
Exposure to cigarette smoke continued in the "smoking" mice throughout pregnancy and lactation until the pups were weaned. The 108 male mice offspring were examined regularly through to adulthood. The researchers investigated damage to the DNA of cells that are involved in the process of producing sperm, sperm counts, the shape of the sperm and how well they swam, and they also investigated the ability of the male offspring to produce their own offspring.
Professor Eileen McLaughlin said that their results showed that male pups of 'smoking' mothers had fewer sperm, which swam poorly, were abnormally shaped and failed to bind to eggs during in vitro fertilisation studies. Consequently, when these pups reach adulthood they were sub fertile or infertile.
The researchers say that even if male offspring were not exposed to cigarette smoke again after they had been weaned, the permanent damage to sperm DNA caused by smoke exposure in the womb and during breast feeding could give rise to an increased susceptibility to cancer and congenital malformations in offspring of these mice.
The study is published online in Human Reproduction.