Taking common painkillers including paracetamol during pregnancy could make grandchildren infertile, research suggests.

Previous studies have found that the drug ibuprofen could harm the fertility of girls. Women are advised to avoid the medication during pregnancy, and told that if pain relief is needed, they should take paracetamol, but for as little time as possible.

However, the new study found that both drugs could harm future fertility of subsequent offspring - with an impact on boys as well as girls. Estimates suggest around one in three will take such drugs during pregnancy.

The study found that the medication made marks on the DNA, with permanent consequences. Ovaries exposed to paracetamol for one week had more than 40 per cent fewer egg-producing cells. After ibuprofen exposure, the number of cells was almost halved.

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Testicular tissue exposed to painkillers in a culture dish had around a quarter fewer sperm-producing cells after exposure to paracetamol or ibuprofen.

Scientists at the University of Edinburgh looked at the effects of paracetamol and ibuprofen on samples of human fetal testes and ovaries.

They found similar effects using several different experimental approaches, including lab tests on human tissue samples and animal studies.

Human tissues exposed to either drug for one week in a dish had reduced numbers of cells that give rise to sperm and eggs, called germ cells.

Girls produce all of their eggs in the womb, so if they are born with a reduced number it could lead to an early menopause.

The team also tested the effects of painkiller treatment on mice that carried grafts of human fetal testicular tissue. These grafts have been shown to mimic how the testes grow and function during development in the womb.

After just one day of treatment with paracetamol, the number of sperm-producing cells had dropped by 17 per cent. After a week of drug treatment, there were almost one third fewer cells.

The scientists found that exposure to paracetamol or ibuprofen triggers mechanisms in the cell that make changes in the structure of DNA, called epigenetic marks.

These marks can be inherited, helping to explain how the effects of painkillers on fertility may be passed on to future generations.

The study, published in Environmental Health Perspectives, was funded by the Medical Research Council, Wellcome and the British Society of Paediatric Endocrinology and Diabetes.

Dr Rod Mitchell, who led the research at the University of Edinburgh, said: "We would encourage women to think carefully before taking painkillers in pregnancy and to follow existing guidelines - taking the lowest possible dose for the shortest time possible."