New evidence says pregnant women who had the flu or a fever lasting more than a week may be at a higher risk of developing a child with autism.
The large Danish study looked at nearly 97,000 children born between 1997 and 2003.
The mothers in the study were screened to see if they had any infections, used antibiotics or had long periods of fever during their pregnancies.
Researchers found no association between autism and minor infections, such as respiratory ailments, or urinary infections.
But, when it came to influenza, the risk of being diagnosed with an autism spectrum disorder before the age of three was twice as high in children when compared to mothers who did not have the flu during pregnancy.
In mothers who had a fever lasting more than a week, the risk was three times greater for developing autism.
Researchers also found mothers who took antibiotics during their pregnancy had a small risk of having a child with autism.