But the findings should not be cause for alarm, says study researcher Richard Beasley, MD, professor of medicine at the Medical Research Institute of New Zealand. "It is still considered a safe drug to take and our findings don't alter that recommendation.”
What is not known, he tells WebMD, is whether the link between the use of painkillers during pregnancy and asthma in the child is truly cause and effect.
"The message would be that this study raises some concern, and that it really reinforces the general principle to avoid unnecessary medication during pregnancy," he says. "This [report] does not change the recommendation."
Acetaminophen, called paracetamol in New Zealand, would ''remain as the preferred analgesic'' to bring down fever in a pregnant woman, he says. "But we would caution against the regular use, particularly regular unnecessary use, during pregnancy.”
The report is published in the journal Clinical & Experimental Allergy.
Previous research, including some by the New Zealand researchers, has suggested that use of the painkiller during pregnancy may increase asthma risk in children.
In the new report, Beasley and his colleagues re-evaluated the results of six previously published studies.
Overall, Beasley found that the use of the painkiller by pregnant women during any stage of pregnancy was linked with a 21% increased risk of asthma in their young children.
The increasing use of acetaminophen, some experts say, may have contributed to the rising rates of asthma worldwide. In the U.S., 24.6 million people, about 8.2% of the population, have asthma, according to the CDC.
In the six studies, the children ranged in age from 2 1/2 to 7. Parents were asked if their child had wheezing in the last 12 months.
"'We would say wheezing is a marker for asthma," Beasley tells WebMD.
No information was available on the dose of painkiller taken or how often.
The results from the separate studies vary. One Spanish study, for instance, found a link between the use of acetaminophen by the mother at least once a month during pregnancy and the chance her child had wheezing by preschool age. But the link was only found among mothers without asthma, not those who had asthma.