Women's use of paracetamol at the end of their pregnancy could be putting their unborn children at increased risk of autism (ASD) and attention deficit hyperactivity disorder (ADHD), a new study has found.
But some experts say more research needs to be done before mothers-to-be are warned not to take the common over-the-counter painkiller.
Scientists at the Johns Hopkins University Bloomberg School of Public Health in the US tested the amount of paracetamol in the umbilical cords of nearly 1000 kids.
"They found a significant, dose-dependent relationship between cord blood levels of either unaltered paracetamol or several of its metabolites and rates of both ADHD and ASD," said Prof Jeffrey Keelan, deputy director of the Women and Infants Research Foundation at the University of Western Australia.
That was after adjusting for smoking, alcohol and drug use, their weight, education status, ethnicity and other factors.
"The strengths of the study are that, for the first time, we have actual blood paracetamol measurements to link exposure and dose with outcome, rather than indirect evidence of exposure at some point in pregnancy," said Prof Keelan.
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The exact causes of ASD and ADHD are unknown, but they have previously been linked to a wide range of factors, including genetics, the age of the parents, infections, autoimmune diseases, antidepressants and gestational diabetes.
"There is biological plausibility for these findings," said Prof Elizabeth Elliott from the University of Sydney's Faculty of Medicine and Health.
"Paracetamol readily crosses the placenta, in animal models has been shown to damage nerves in the brain, and in humans has been associated with ADHD and other disorders."
But both she and Prof Keelan said we shouldn't jump to conclusions. Prof Elliott said there was a high rate of developmental disabilities in the cohort of children looked at, which had no explanation, and the mothers' drinking habits were boiled down to a 'yes' or 'no' answer, with no details on how often or how heavily they drank.
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Other experts said while the measurements would show paracetamol use at the end of the pregnancy, there was little information on how much the mothers had taken over the previous 40 weeks - especially in the second trimester, which previous research has singled out as the most important period for the baby's developing brain.
"The subgroup analysis suggests higher risks for lead and bottle feeding than for paracetamol, something the authors do not comment on," said neurologist Prof Norman Saunders of the University of Melbourne.
"One must also be cognisant of the fact that a statistical association is not equivalent to causation," said Dr Alex Polyakov, University of Melbourne obstetrician.
"Nothing in this study indicates that an occasional intake of a couple of Panadol tablets while pregnant would have any effect on the risk of ADHD/ASD."
The research was published on Thursday in journal JAMA Psychiatry.
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