After conducting tests on human tissues, researchers from the University of Edinburgh in the United Kingdom have found that painkillers taken by pregnant women may affect their unborn child's fertility later in life.
Researchers stressed advice for pregnant women remained unchanged.
As of now, guidelines say that, if necessary, paracetamol - also known as acetaminophen - should be used at the lowest possible dose for the shortest possible time. Ibruprofen, meanwhile, should be avoided during pregnancy.
"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", said Dr. Rod Mitchell who led the research in the MRC Centre for Reproductive Health at the University of Edinburgh.
According to the Australian government's Health Direct website, "Paracetamol, which is not a Nonsteroidal anti-inflammatory drug (NSAID), is usually recommended as a safer choice than ibuprofen but check the reason for pain with your midwife, doctor or pharmacist". "However, over the previous year, a growing number of reports have suggested that we might need to take a closer look at their safety in unborn babies".
Scientists at the university studied the impact of paracetamol and ibuprofen across a series of tests created to establish how they impact on the unborn child. Germ cells refer to the reproductive cells in the body, which are egg cells in females and sperm cells in males.
The study looked at the effects of Paracetamol and ibuprofen on samples of human foetal testes and ovaries.
After just one day of treatment with a human-equivalent dose of Paracetamol, the number of sperm-producing cells in the graft tissue had dropped by 17%.
Human tissue exposed to either drug for one week in a dish had reduced numbers of germ cells that give rise to sperm and eggs, cells, the study found.
The researchers also found that ovaries exposed to paracetamol for one week had more than 40 percent fewer egg-producing cells, and those exposed to ibuprofen had a almost 50 percent reduction in cells. After ibuprofen exposure, the number of cells was nearly halved.
Experts said this was important because 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 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. This affected their fertility and the fertility of females in subsequent generations.
Testicular tissues exposed to paracetamol or ibuprofen had around a quarter fewer sperm-producing cells, the scientists said. These marks can be inherited, helping to explain how the effects of painkillers on fertility may be passed on to future generations.
The team also found that painkillers could have an effect on germ cells by affecting hormones called prostaglandins, which play a key role in the functions in the ovaries and testes.