Scientists have found an elevated rate of language delay in girls at 30 months old born to mothers who used acetaminophen (also known as paracetamol) during pregnancy.
Acetaminophen is the active ingredient in Tylenol and hundreds of over-the-counter and prescription medicines. It is commonly prescribed during pregnancy to relieve pain and fever.
This is the first study to examine language development in relation to acetaminophen levels in urine.
Information was gathered from 754 women who were enrolled into the study in weeks 8-13 of their pregnancy.
Researchers at Icahn School of Medicine at Mount Sinai in the US asked participants to report the number of acetaminophen tablets they had taken between conception and enrolment, and tested the acetaminophen concentration in their urine at enrolment.
The frequency of language delay, defined as the use of fewer than 50 words, was measured by both a nurse's assessment and a follow-up questionnaire filled out by participants about their child's language milestones at 30 months.
Acetaminophen was used by 59 per cent of the women in early pregnancy, according to the study published in the journal European Psychiatry.
Acetaminophen use was quantified in two ways: High use vs no use analysis used women who did not report any use as the comparison group. For the urine analysis, the top quartile of exposure was compared to the lowest quartile.
Language delay was seen in 10 percent of all the children in the study, with greater delays in boys than girls overall.
However, girls born to mothers with higher exposure - those who took acetaminophen more than six times in early pregnancy - were nearly six times more likely to have language delay than girls born to mothers who did not take acetaminophen.
These results are consistent with studies reporting decreased IQ and increased communication problems in children born to mothers who used more acetaminophen during pregnancy.
Both the number of tablets and concentration in urine were associated with a significant increase in language delay in girls, and a slight but not significant decrease in boys.
Overall, the results suggest that acetaminophen use in pregnancy results in a loss of the well-recognised female advantage in language development in early childhood.
"Given the prevalence of prenatal acetaminophen use and the importance of language development, our findings, if replicated, suggest that pregnant women should limit their use of this analgesic during pregnancy," said Shanna Swan, from the Icahn School of Medicine at Mount Sinai.
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