National Institute for Health and Clinical Excellence (NICE)
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Smoking in pregnancy linked to fertility problems
The findings add further weight to calls for mothers to stop smoking before trying for a baby, and follows the release of NICE guidance on helping women give up smoking in pregnancy and following childbirth.
The guidance recommends that midwives assess every woman's carbon monoxide levels at their first antenatal appointment by encouraging women to have a special breath test.
This can determine whether women smoke or are being exposed to passive smoking, thereby ensuring that they receive appropriate support for the good of their unborn baby.
For this latest study, researchers at the University Hospital of Copenhagen, in Denmark, looked at 24 embryonic testes obtained after women had undergone legal termination between 37-68 days after conception.
They also took blood and urine samples and questioned the women about their lifestyle during pregnancy, including smoking and drinking habits.
The study, published online in the journal of Human Reproduction, found that a mother's smoking during early pregnancy halved the numbers of germ cells (the cells that form eggs in females and sperm in males) and reduced the number of somatic cells (the cells that form every other part of the body) by more than a third in the developing foetus. It is believed that this may have an adverse effect on the fertility of the baby in later life.
A greater reduction in germ and somatic cells was seen in embryos from the mothers who smoked the most. This remained the same, even after adjusting for other risk factors such as coffee and alcohol consumption.
Lead researcher Claus Yding Andersen, Professor of Human Reproductive Physiology at the University Hospital of Copenhagen, said: "As the germ cells in embryos eventually develop to form sperm in males and eggs in females, it is possible that the negative effect on the numbers of germ cells caused by maternal smoking during pregnancy may influence the future fertility of offspring."
"In addition, the reduction in the number of somatic cells also has the potential to affect future fertility, as somatic cells in the testes support the development of germ cells to form functional sperm. If the somatic cell number is reduced, fewer functional sperm will be produced."
Professor Andersen added that the study results in combination with the other known negative effects of cigarette smoke during pregnancy "further emphasises that pregnant mothers should refrain from smoking."
Dr. Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield said that the study "elegantly provides further support for the theory that the most critical time which determines how fertile an adult will be is actually in the time before they were born."
"This is a hard concept to grasp, but given the knowledge that women are born with the entire supply of eggs, and men are born with the number of sperm producing cells, they will ever have means that what mothers are exposed to during pregnancy can be vitally important for the reproductive health of their children when they reach adulthood."
"Once a woman is pregnant, is it vitally important that she does not smoke and that the baby is not exposed to the harmful chemicals contained in cigarette smoke whilst it is developing."
"It breaks my heart to see pregnant women having a crafty cigarette outside the Maternity hospital in Sheffield where I work. That is not the best start in life for any baby. But equally we need to recognise that for some people stopping smoking is hard and we need to support them to give up," added Professor Pacey.