Paracetamol is recommended for pain relief during pregnancy. But recent results have indicated that prenatal exposure may affect development of the male brain and reproductive tract.
In a study in Reproduction
(online, 30 May 2017), researchers exposed pregnant mice to paracetamol or a precursor, aniline, from seven days after conception to delivery.
They found that male adult offspring exposed to the highest dose of paracetamol had around a 50% reduction in neurons in a region of the hypothalamus critical for brain masculinisation, compared with male mice born to control-treated mothers. Paracetamol-exposed mice also showed altered sexual behaviour, including changes in urinary marking behaviour, reduced territorial aggression towards other males and failure to ejaculate during mating.
Given that the highest dose of paracetamol was less than the equivalent taken by women during pregnancy, the researchers say these findings indicate that its use during pregnancy could have effects on male brain development in humans.
 Hay-Schmidt A, Ejlstrup Finkielman O, Jensen B et al. Prenatal exposure to paracetamol/acetaminophen and precursor aniline impairs masculinisation of male brain and behaviour. Reproduction 2017;154:145–152. doi: 10.1530/rep-17-0165