Many studies from recent years have started to examine the potential long-term effects of taking certain painkillers during pregnancy. 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.

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

"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.

The researchers tested the effects of paracetamol and ibuprofen on samples of human fetal testes and ovaries. After an exposure period of one week, a reduction in the number of germ cells was observed. Germ cells refer to the reproductive cells in the body, which are egg cells in females and sperm cells in males.

While the paracetamol exposure led to a 40 percent decrease in these cells, the ibuprofen exposure resulted in a 50 percent decrease. Researchers point to the effect this has on the future of female children as all their eggs are produced in the womb. Girls are typically born with around two million eggs in their ovaries. This supply is slowly depleted over the course of 40 to 50 years. However, being born with a reduced number of eggs could lead to an early menopause.

In the case of unborn male children, sperm-producing cells reduced by nearly 25 percent after the testicular tissue was exposed to paracetamol or ibuprofen. Similar results were observed in tests conducted on mice that carried grafts of human fetal testicular tissue. While a single day of exposure to human doses of paracetamol led to a 17 percent decrease of sperm-producing cells, a week of exposure saw almost one third fewer cells.

According to the researchers, the painkillers act on molecules called prostaglandins which have important functions in the ovaries and testes. It is believed that paracetamol or ibuprofen may leave inheritable marks (known as epigenetic marks) that make changes to the structure of DNA, passing on the effects of the painkillers to future generations.

Current guidelines in the U.K. recommend that pregnant women limit their use of paracetamol and avoid ibuprofen. The researchers stated that this advice remains unchanged.

Dr. Patrick O’Brien, consultant obstetrician and spokesman for the Royal College of Obstetricians and Gynaecologists, added that further research was required before firm conclusions could be drawn. 

"Women should not be alarmed by the results of this study. Paracetamol is widely accepted as a safe painkiller for pregnant women to take, and can be very beneficial when a pregnant woman is suffering with a migraine, for example," he stated.