Pregnant women who take painkillers may be harming the fertility of their unborn sons as well as daughters, researchers have warned.
Scientists have previously said ibuprofen and paracetamol reduce the number of cells that would eventually become ovaries.
But now a British team has discovered they have the same effect on cells that would later produce sperm in boys.
Painkillers may also affect the fertility of future generations by triggering changes in DNA structure which can be inherited, the research found.
The findings add to the growing body of evidence that pregnant women should be wary of taking painkillers.
Current guidelines state they should avoid ibuprofen – due to its link with a range of complications. They can take paracetamol, but ideally at the lowest possible dose, for the shortest possible duration.
Aspirin is thought to be safe in low doses and some women are prescribed daily pills to reduce the risk of miscarriage.
In the latest study, Edinburgh scientists looked at the effects of paracetamol and ibuprofen on foetal samples of the testes and ovaries.
They found that after one week of being exposed to paracetamol, the number of egg-producing cells was reduced by 40 per cent.
The effect of ibuprofen was even greater and the number of egg-producing cells was almost half.
Scientists also found that paracetamol and ibuprofen reduced the number of sperm-producing cells by a quarter.
The British study is the first to examine the effects of painkillers on girls’ and boys’ fertility, and to try to identify what is happening to cells.