Painkillers in pregnancy linked to sons' fertility

New preliminary research suggests a possible link between the use of mild painkillers during pregnancy and the birth of male children with congenital cryptorchidism, more commonly known as undescended testes, a condition which reduces male fertility. The rates of undescended testes seen in the study remained relatively low.

The researchers found that the risk of congenital cryptorchidism was not significantly increased by overall use of mild analgesics such as paracetamol, ibuprofen or aspirin during pregnancy compared with no use. However, the researchers also studied several subgroups and found that while there was no link between use of painkillers in the first trimester and the condition, use in the second trimester more than doubled the likelihood of male babies being born with the condition. The risk of the disorder was also increased in women reporting using painkillers for more than two weeks.

Professor Richard Sharpe, from the Medical Research Council, explained that the second stage of pregnancy was the final stage of testes development, where disruption was most likely. But he told the Daily Mail: 'It is important to say it was prolonged use of painkillers that had the biggest effect. Taking one or two painkillers occasionally for a headache is not going to affect the baby'.  

The study featured an analysis of pregnant women's medication use and animal research looking at the fetal development of rats under exposure to painkillers. In the first phase, the researchers surveyed the medication use of 2,297 Danish and Finnish pregnant women and assessed the prevalence of cryptorchidism in the newborn male babies. The majority of the women were questioned using a written questionnaire during their third trimester and a relatively small number undertook a telephone interview.

More women reported using mild painkillers when interviewed over the telephone and the main findings were based on these 491 women. In the second phase of the study, the researchers assessed the impact of exposure to painkillers on the development of rat fetuses. They found that exposure to painkillers reduced the anogenital distance, the size of the perineum, in the males of the litters, suggesting a reduced exposure to testosterone.

Dr Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield, explained that to date there have been relatively few concrete examples of the effects chemicals a mother may be exposed to during pregnancy on the reproductive health of male babies and much of the research so far has been 'theoretical'. 'Clearly further research is needed as a matter of priority', he said.

Current guidance advises pregnant women to avoid medication and, if needed, to use paracetamol rather than ibuprofen or aspirin. The collective results, soon to be published in Human Reproduction, suggest that the use of mild painkillers in pregnancy may have an effect on fetal development but due to the small size of the study, the evidence does not yet point to a definite link.