Why We Know So Little About Medicines During Pregnancy

"I explained to the baby's mother that I planned to order acetaminophen-commonly sold over the counter as Tylenol-every six hours, because the baby had an obvious source of pain. If pain still kept the baby from eating, sleeping, or calming down, the mother could ask for an opioid. I was just leaving the room when the mother stopped me to ask about the acetaminophen."

"When I sat down at a hospital computer, I was surprised to find that the mother's question had a basis in mainstream research. Small studies had associated acetaminophen exposure in utero with a baby's risk of developing autism. But this wasn't the same as saying that Tylenol caused autism. Perhaps whatever the drug was treating-for example, fevers, infections, or painful chronic conditions-contributed to autism, and acetaminophen did not."

"For babies under three months, as for pregnant women, Tylenol is considered the safest medicine for fever. I continued to order it for patients, if a little more cautiously. Then, in 2024, a more rigorously controlled study of more than two million children born in Sweden found no connection between acetaminophen and neurodevelopmental disorders. As the epidemiologist Katelyn Jetelina has written, "the evidence leans heavily towards correlation, not causation. (Tylenol is not the cause.)""

A pediatrics resident admitted a two-month-old infant for observation after minor surgery and discussed scheduled acetaminophen dosing every six hours with the mother, offering opioids if pain persisted. The mother asked whether acetaminophen causes autism. Small studies had associated in utero acetaminophen exposure with increased autism risk, but correlation and causation were distinguished, and underlying conditions treated by acetaminophen could contribute to outcomes. Tylenol remains considered the safest fever medicine for pregnant women and infants under three months, while NSAIDs carry kidney risks. A 2024 Swedish study of over two million children found no link to neurodevelopmental disorders.

Read at The New Yorker