Despite many health dangers that can be caused by smoking during pregnancy, as much as 20% of young mothers in the United States continue to smoke during pregnancy. But that evidence, those reasons not to, keep building. The latest comes from the University of Newcastle in Australia, a study in which researchers found that smoking during pregnancy can negatively affect the fertility of sons later on in life.
Led by Professor Eileen McLaughlin, the researchers noticed in their Human journal publication that, until now, the effects of smoking during pregnancy on male offspring fertility – as well as the mechanisms behind this – have been unclear, due to a lack of animal studies with carefully controlled environments and exposure to toxic chemicals.
However, their latest study has used a comprehensive animal model to better examine just how smoking during pregnancy can affect the fertility in male offspring. This model used mice, which best mimics human smoking without deliberately exposing pregnant mothers and their offspring to cigarette toxins, McLaughlin said.
To conduct their study, researchers used a machine that pulls smoke into a nose piece and then blows it into the airways of the mice. It was placed on 27 females who inhaled the smoke into their lungs at a rate that is equivalent to 24 cigarettes a day in humans for six weeks prior to conception. Another group of 27 mice, a control group, were exposed only to normal air during that time. Exposure to either normal or smoke filled air continued on through pregnancy and lactation, right up until the point that their pups were weaned.
From birth on into adulthood, researchers examined the 108 male mice offspring regularly, inspecting damage to the DNA of cells involved in producing sperm, sperm counts, sperm shape, how well the sperm swam, and the ability of the male offspring to reproduce. What they found was that the smoking mothers had produced male pups with fewer sperm that swam poorly, were abnormally shaped, and didn’t bind well to eggs during in vitro fertilization.
“Consequently, when these pups reach adulthood, they are subfertile or infertile,” McLaughlin told Medical News Today. “This is the first time we have been able to prove conclusively that male baby exposure to cigarette toxins in pregnancy and early life will damage later life fertility.”
McLaughlin went on to explain how it is already known that cigarette toxin exposure can affect stem cell population in the testes and reduce the amount of sperm produced. Additionally, the oxidative stress from cigarette toxins can damage cells in the testes, which can result in sperm with “abnormal head and tails that are unable to swim properly or successfully bind and fuse with eggs.”
Of course, there are some limitations to the study, including the fact that it was conducted on mice instead of humans. Still, McLaughlin says that it does have human implications and that the model does stimulate human cigarette exposure. And we do have some real life evidence – men currently in their 30s and 40s that were exposed to cigarette toxins in utero back when the negative health effects of smoking during pregnancy were less well known.
“These men have difficulty conceiving and this is associated with production of low numbers of poor quality sperm in their semen,” McLaughlin said. “Unfortunately, about 25% of young women today continue to smoke when they are pregnant or breastfeeding – thereby potentially damaging their sons’ fertility.”
To remedy the potential issue, McLaughlin and her team say that smoking cessations programs should continue to advocate that women need to avoid smoking during pregnancy and breastfeeding. In the meantime, she and her team plan to test the effect of cigarette exposure in the sons, grandsons, and even great-grandsons of mice mothers who smoked during pregnancy. They also plan to place some emphasis on the health implications for the eggs of female offspring when smoke exposure has occurred.
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