Common pain killers consumed by mother during pregnancy can affect the long term reproductive function of her son.

These pain killers are easy to get, over-the-counter drugs approved for usage before public awareness campaigns began on their detrimental side effects on hormone function and reproductive health.

The lead author of this study claims that the effect of a single 500mg paracetamol tablet during entire pregnancy is greater than the combined effect of exposure to 10 naturally found chemicals.

The physiological explanation given is that the same mechanism of operation of painkillers that cures headaches among others impacts the male fetus by affecting testosterone production.

Although most women delivered healthy boys, this study found that the risk of cryptorchidism in infant boys is slightly elevated if mother consumed paracetamol, aspirin or ibuprofen.

Cryptorchidism is the scientific word for undescended testicles at birth. Henrik Leffers team at University Hospital of Copenhagen, Denmark followed pregnancies of 834 women. Comparing the results, Cryptorchidism risk was found to be slightly raised (42 children out of 834).

With pain killers, the risk multiplied by a factor of 1.43. Interestingly, this condition also occurred when painkillers were not taken (in 15 of 42 boys). Healthy boys were delivered by 249 women on painkillers. In a separate analysis, Scientists calculated an increase in the risk rate (by 2.47%) when the dosage was brought up or while taking more than one painkiller.

In a Danish study, risk of cryptorchidism multiplied by 1.33% when paracetamol is consumed during pregnancy.

Testosterone is required for formation of male testis. Its production reduced by 50% in pregnant rats given the same dosage prescribed for pregnant women.

Dr Leffers advocates no paracetamol during second trimester of pregnancy when testicles develop. He adds that women withholding information was the main reason an earlier study in Finland study found no relation between painkillers and cryptorchidism. The Denmark study succeeded because of its questionnaires and telephonic interviews.