The most common reasons the women in the study used acetaminophen in pregnancy was to treat pain, fever and flu.
The study - led by the Norwegian Institute of Public Health in Oslo - is published in the International Journal of Epidemiology.
Acetaminophen - also known as paracetamol - is one of the most widely used of all drugs. It is used to relieve fever and pain, including headache, muscle ache, backache, toothache, sciatica and arthritis pain. Common brand names include Tylenol, Calpol and Panadol.
First author of the new study, Dr. Maria Magnus, notes that "uncovering potential adverse effects is of public health importance, as paracetamol is the most commonly used painkiller among pregnant women and infants."
Previous research has linked acetaminophen exposure in pregnancy and infancy to asthma development, but it has not been clear if this link is independent of the reason for taking the medication.
For their study, Dr. Magnus and colleagues analyzed data from the Norwegian Mother and Child Cohort Study. Altogether, the study covered 114,500 children and their mothers.
Early acetaminophen exposure, childhood asthma independently linked
The researchers compared links between several conditions during pregnancy - with and without use of acetaminophen - and asthma developing at age 3-7 years in the children.
In their analysis they also investigated the likelihood of the link being due to the most common reasons for acetaminophen use by pregnant women: pain, fever and influenza.
The team found that 5.7% of the children had asthma at age 3, and 5.1% had it at age 7.
The analysis showed that overall, asthma at 3 years was independently linked to prenatal acetaminophen exposure and use of acetaminophen during infancy (age 0-6 months). The results were consistent for asthma at 7 years.
The strongest link between prenatal exposure to acetaminophen and having asthma at age 3 was with the mother using the drug for more than one reason.
Other studies have found no link between asthma in offspring and mothers' use of acetaminophen outside pregnancy or fathers' use of the drug.
The new study confirms these previous findings and supports the conclusion that the results are not due to underlying factors or health behaviors shared by the parents but due to the drug itself.
Findings warrant no changes to current recommendations
After a recent review of pain medication use in pregnancy - including acetaminophen - the Food and Drug Administration (FDA) did not change their advice that pregnant women "should always consult with their health care professional before taking any prescription or OTC [over the counter] medicine."
The authors of the new study were keen to emphasize that their findings do not warrant making changes to recommendations regarding the use of acetaminophen in pregnancy.
Acetaminophen is an active ingredient in hundreds of OTC and prescription medicines, and it is also combined with other active ingredients in medicines that treat allergy, cough, colds, flu and sleeplessness.
The drug can cause serious liver damage if used more than directed.
In the 1980s, acetaminophen became the mainstay pain reliever and fever reducer for children after aspirin was linked to Reye's syndrome, an extremely rare condition that can cause serious liver and brain damage.
Meanwhile, Medical News Today recently learned of some good news for chocolate-loving mothers-to-be: it appears that eating 30 g chocolate a day during pregnancy may benefit fetal growth and development.