Taking paracetamol during pregnancy has been linked to fertility problems in unborn children, a study has suggested.
The research was conducted on rats which have similar reproductive systems to humans.
Pregnant rats who were given paracetamol and indomethacin, a drug similar to aspirin, gave birth to offspring which had fewer eggs than those who were not.
Scientists at the University of Edinburgh's MRC Centre for Reproductive Health also found that the rats had smaller ovaries, and produced less babies.
Infant male rats, meanwhile, created fewer cells that give rise to sperm, but fertility reached a normal level when the animals reached adulthood.
Paracetamol is commonly used to treat mild to moderate pain, including headaches and the symptoms of colds.
Indomethacin, however, is only available on prescription and for pain in arthritis as well as reducing inflammation.
Professor Richard Sharpe, from the University of Edinburgh's MRC Centre for Reproductive Health, who co-led the study published in the journal Scientific Reports, said: “It's important to remember that this study was conducted in rats, not humans. However, there are many similarities between the two reproductive systems.
Further research is now needed to understand how the drugs affect a baby’s reproductive development in the womb.
Co-author Professor Richard Anderson, also from the University of Edinburgh, said: ”These studies involved the use of painkillers over a relatively long period. We now need to explore whether a shorter dose would have a similar effect, and how this information can be usefully translated to human use.“
Professor Adam Balen, chairman of the British Fertility Society, called the study "interesting" but said caution must be taking when exptrapolating the findings to humans.
"It is sensible for pregnant women to minimise use of paracetamol and other painkillers and seek medical advice if they experience problems with significant pain in pregnancy."
The Medicines and Healthcare products Regulatory Agency (MHRA), which issues guidance on medicines, said the study findings would be "carefully evaluated".
A spokesman said: "Women should avoid taking medicines during pregnancy unless absolutely necessary and should speak to their doctor, midwife or pharmacist before doing so.
"Paracetamol is generally considered to be a safe treatment for pain relief during pregnancy but should be taken at the lowest possible dose for the shortest time."
Researchers gave rats the drugs over several days, and saw changes in between one to four days, as rats have faster foetal development than humans.
The drugs appeared to affect the mother’s offspring, but also created changes that lasted into the granddaughters of the animals.
Scientists believe that some painkillers may change the way that “germ cells” – which later become eggs and sperm – grow in the womb.
The drugs may alter hormones known as prostaglandins which control ovulation, as well as the menstrual cycle and labour.
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