Paracetamol (acetaminophen) is the most commonly used medicine in pregnancy, yet there are very few studies that have investigated the possible long-term consequences for the child.
The new study from the Norwegian Institute of Public Health used data from the Norwegian Mother and Child Cohort Study to investigate the effect of paracetamol during pregnancy on psychomotor development, behaviour and temperament at 3 years of age.
Almost 3,000 sibling pairs were included in the study.
By comparing children who were exposed to paracetamol during pregnancy with unexposed siblings of the same sex, researchers could control for a variety of genetic and environmental factors, in addition to other important factors such as infections, fever, use of other medications, alcohol intake and smoking.
The study found that children who had been exposed to paracetamol for more than 28 days of pregnancy had poorer gross motor skills, poor communication skills and more behavioural problems compared with unexposed siblings.
The same trend was seen with paracetamol taken for less than 28 days, but this was weaker.
To investigate whether the underlying illness could be the cause of the effect on the children, and not paracetamol itself, the researchers examined a different type of analgesic with another type of mechanism of action (ibuprofen).
The researchers did not find any similar long-term effects after use of ibuprofen.
"The results strengthen our concern that long-term use of paracetamol during pregnancy may have an adverse effect on child development, but that occasional use for short periods is probably not harmful to the foetus," said Professor Hedvig Nordeng at the School of Pharmacy, University of Oslo.
"Importantly, we cannot assume that there is a causal relationship between maternal use of paracetamol during pregnancy and adverse effects in children from an epidemiological study.
"Since this is the only study to show this, there is a need for further research to confirm or refute these results," Nordeng said.
The study was published in the International Journal of Epidemiology.