Doctors are already facing worried women asking whether taking Tylenol during pregnancy can cause autism in their children just days after US President Donald Trump urged women to "fight like hell" to not take it.

Trump, at a White House press conference on Monday flanked by Health Secretary Robert F. Kennedy Jr. and senior health officials, warned women of the autism link, despite scant scientific evidence, and said his administration would add warnings to drug labels to highlight the risk.

The day after the press conference, Dr. Rana Alissa, a paediatrician in Jacksonville and president of the Florida Chapter of the American Academy of Paediatrics, was covering a shift in her hospital's newborn nursery along with an obstetrician-gynaecologist.

"Pregnant women were asking about Tylenol actively," she said. "'What should I do? Do you think it's safe? I just took Tylenol last month. Do you think I already hurt my baby?' These are examples of the questions we're hearing."

Dr. Rachel Blake, an obstetrician-gynaecologist based in New York and New Jersey, said she had reassured several pregnant patients on Tuesday that it was still safe to take Tylenol despite Trump’s repeated admonitions.

“There has been no new research that suggests there should be a change in that guideline,” she said.

Blaming pregnant women creates guilt

Linking use of Tylenol during pregnancy to autism heaps blame on pregnant women, who already have a lot of guilt and fear if they have to take anything while pregnant, said Dr. Sindhu Srinivas, president of the Society for Maternal-Fetal Medicine.

"Patients are definitely asking about it," she said, referring to Trump's warnings. "If they have taken it already or took it at some point in the pregnancy, there is a lot of concern," she said.

Her group is among the dozens of medical, research and autism advocacy groups - including the American College of Obstetricians and Gynecologists and Tylenol maker Kenvue - who have decried the president's comments.

Kenvue has said independent, sound science shows taking the drug does not cause autism. It is sold by generic drugmakers as acetaminophen in the U.S. and paracetamol in other nations.

On Monday, the U.S. Centers for Disease Control and Prevention updated its website and the U.S. Food and Drug Administration sent letters to providers warning of a risk, with the caveat that no causal relationship between acetaminophen and autism had been established.

Since Monday, European Union health officials, British health agencies and the World Health Organization have rushed to correct the record. All said there is no conclusive evidence linking use of the painkiller during pregnancy and autism.

Srinivas's approach to counseling patients is to share some of the shortcomings and nuances about the research supporting an association between Tylenol during pregnancy and autism.

Some of the studies, she said, had "a lot of limitations" and failed to take into account the reasons a pregnant woman might need to take acetaminophen, such as fever, which has been linked with autism.

"What we know is there is really no causal link between acetaminophen and autism," Srinivas said.

Untreated fever raises birth defect risk

Acetaminophen is the only pain reliever considered safe for pregnant women. Doctors already urge them to use the least amount of the drug for the shortest possible duration to control pain and fever during pregnancy.

Untreated fever and pain during pregnancy are known to increase the risk of birth defects, preterm birth, low birth weight and miscarriage and other health problems.

"The risk of fever in pregnancy is very real," said Dr. Caitlin Baptiste, maternal fetal medicine specialist at Columbia University Irving Medical Center in New York.

"Certainly in the first trimester, we know it can cause congenital birth defects and can raise the risk of neurodevelopmental disorders," she said.

Baptiste said she is glad for the increased focus on autism, but does not think it's helpful to add unfounded worries about Tylenol use. "We need to focus efforts on where the science is," she said.

Caring for children with conditions like autism can already be “exhausting, terrifying, alienating,” said Erin Erenberg, the CEO and co-founder of Chamber of Mothers, a maternal rights advocacy group with more than 100,000 members across the United States.

Erenberg, who herself has a “medically complex” child, said the Trump administration’s continuing erosion of trust in evidence-based health guidance “leaves women vulnerable to misinformation."