Researchers at the University of Toronto, Canada, have discovered a link between smoking before and after pregnancy and subsequent infertility in the offspring, particularly in female children born to mothers who smoke.
It has been known for decades that if a mother smokes during pregnancy, she puts her child at risk of birth defects, respiratory conditions like asthma, lung cancers, nicotine addiction and even an increased risk of crib death, stillbirth and premature delivery.
However, doctors had discovered that those mothers who smoked before conception (but gave up during pregnancy) and then continued to smoke after the birth have a risk of causing infertility in their daughters.
Smoking produces substances called polycyclic aromatic hydrocarbons (PAHs), which are toxins found in cigarettes. The researchers injected these PAHs into mice before conception and during lactation. Another group of mice was not exposed to PAHs at all, and a final group were only exposed during lactation and not during pregnancy.
The mice in the first group who were exposed during pregnancy all had normal litters of mice pups who were apparently healthy, but it was found that their female pups had reduced follicles which meant they were unable to produce a healthy number of eggs. Their follicles were reduced by a massive 70%. This finding could be significant (especially if followed up with human studies) in explaining why the infertility rate in humans has increased so much in the last few decades. The other groups had normal pups.
Researchers then transplanted human ovarian tissue into the first group of mice to see if the PAHs have a similar effect on human tissue. The PAHs caused the ovarian tissue to die.
Dr. Andrea Jurisicova, the lead researcher, said
‘Mice mothers exposed to PAHs (environmental pollutants found in cigarette smoke, car exhaust fumes, smoke produced by fossil fuel combustion as well as in smoked food) before pregnancy and during breastfeeding, but not during pregnancy, can cause a reduction in the number of eggs in the ovaries of their offspring by two-thirds. This limits the window in which the daughter will be able to reproduce.’
These mice offspring will continue to be monitored to see if they go through menopause early and to see if any pups they bear have similar inherited fertility problems.
Girls aren’t the only ones to inherit infertility problems. Another recent study in the Journal of Epidemiology showed that boys born to mothers who smoke have lower sperm counts.