Using the painkiller paracetamol during pregnancy for prolonged periods of time could contribute to reproductive disorders in male babies, according to scientific research.
Although paracetamol remains the painkiller considered safest for pregnant women, a study by scientists at the University of Edinburgh adds to existing evidence that too much paracetamol during pregnancy may reduce testosterone levels.
Reduced exposure to testosterone in the womb has been linked to an increased risk of infertility, testicular cancer and undescended testicles.
Pregnant women should continue to follow current NHS guidance that they take paracetamol at the lowest effective dose for the shortest possible time, according to Dr Rod Mitchell from the University.
Dr Martin Ward-Platt from the Royal College of Paediatrics and Child Health, said: "The findings of this study send a clear message - expectant mothers should not prolong paracetamol use during pregnancy, only taking it when necessary and as per current NICE guidelines."
NICE is the UK's National Institute for Health and Care Excellence.
Dr Ward-Platt also pointed out that study concerned paracetamol use over several days and that there could be times during pregnancy when limited paracetamol use might be necessary.
"There are times where one or two doses is needed to treat one-off episodes of fever for example," he said.
The University of Edinburgh study used mice carrying grafts of human testicular tissue.
The mice were given three doses of paracetamol a day over a period of either 24 hours or seven days.
The study found there was no effect on testosterone production following 24 hours, but that after a week of exposure the amount of testosterone produced was reduced by 45%.
(Additional reporting by PA)