Using antidepressants during the second or third trimester is associated with an increased risk of autism spectrum diseases (ASD), according to a new study from Canada.

The study included 1,054 children with ASD aged, on average, 6.2 years at the end of follow-up. Boys outnumbered girls by about 4:1. After adjusting for potential con-founders, the 31 offspring of mothers who took antidepressants during the second or third trimester or both were found to be 87 per cent more likely to have ASD than those who were not exposed to antidepressants.

Taking selective serotonin reuptake inhibitors (SSRIs) during the second or third trimester or both doubled the risk of ASD (hazard ratio 2.17) overall and after controlling for maternal history of depression (hazard ratio 1.75).

The association seems biologically plausible. SSRIs can cross the placenta and serotonin modulates numerous developmental processes, including cell division, neuronal migration, cell differentiation and synaptogenesis. (JAMA Pediatr doi: 10.1001/ jamapediatrics.2015.3356)

A UK study has reported a link between antidepressants and mania or bipolar disorder. See BMJ Open 2015;5:e008341.