The study found a 79 per cent increased risk of autism and a 24 per cent increased risk of depression in children exposed to infection while in utero, as well as an increased risk of suicide.
Researchers analyzed patient data from pregnant women hospitalized between 1973 and 2014 in Sweden.
From a database of nearly 1.8 million children, researchers used hospital codes to determine which babies were exposed to infection. They then tracked those children and their mental health through the years, with some of the oldest babies now entering their forties.
Researchers divided infections into three categories: the first was any infection at all, the second was “severe maternal infections” and the third was “mild maternal infections” (namely, urinary tract infections).
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“We thought of (severe) infections as things that would cause a whole bunch of inflammation in the mother,” researcher Benjamin J. S. al-Haddad told Global News.
“Things like sepsis (when there’s bacteria in the blood), severe pneumonia (where moms need special help breathing because they have such a severe respiratory infection), meningitis or encephalitis (infections around the brain), pyelonephritis (where the kidneys have bacteria and puss), as well as influenza and chorioamnionitis (where the different parts of the placenta become infected over the course of giving birth).”
Researchers hypothesized that something as mild as a UTI would not be linked to such a high increased risk — but they were wrong.
“From our results, it looks like we see similarly increased risk whether the mother had a UTI or something more severe,” al-Haddad said. “It doesn’t seem to matter what kind of infection it is.”
No link was discovered between exposure to infection in utero and other mental conditions, such as bipolar disorder or psychosis.
Researchers worried about other conditions present in mom (such as asthma or diabetes) that could taint the results.
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However, even when they controlled for such conditions, the link between infection and an increased risk for autism and depression remained.
“The things that we controlled for included maternal age, maternal asthma, maternal diabetes, premature rupture of membranes (which is when the sac holding the liquid that the fetus is in breaks before mom goes into labour), maternal tobacco status (whether mom smoked or not), and then we also did special controls for siblings,” al-Haddad said.
The results of the study suggest that infection can “impart subtle brain injuries contributing to the development of autism and depression,” said researchers.
While these results sound scary, al-Haddad stressed that the increased risk is in addition to the preexisting baseline risk.
“In the United States, the risk of autism is one out of every 59 kids. Our results suggest that on top of that baseline, there would be a 79 per cent increased risk. We don’t know what that number would be, but the extra risk conferred on top of a baseline low risk, in terms of the population, is not high,” said al-Haddad. (Autism Speaks Canada reports that one in every 66 children have autism in Canada.)
“This is just one of a myriad of causes that we think increases risk. This is another piece of trying to understand what the causes of autism are and how we can prevent those causes.”
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What does “increased risk” really mean?
It’s important for parents to understand that the reported 79 per cent increase in risk sounds like a big number, but it’s actually quite a small increase on the pre-existing risk.
“It’s still (less than) 1 per cent in terms of the absolute increase (in risk) a particular child has. Basically, that means almost 98 per cent of kids whose mothers have an infection during pregnancy that would cause hospitalization are not born with autism or another neuro-developmental condition,” Dr. Evdokia Anagnostou. She works as a child neurologist and senior clinician scientist at the Bloorview Research Institute.
“So it’s a small absolute risk, but it’s a big risk biologically in the sense that we are learning that there is a mechanism to do with infection that likely interacts with our genes that may increase the chance of developing autism.”
On its own, exposure to infection during pregnancy is not enough to cause autism, but it can be a contributing factor.
“It’s one of the ways that our environment (in this case, infection) may interact with our genes to somewhat increase our risk,” Anagnostou added.
This study is helpful because it explains one of the many different changes that can happen in the brain and the body that can contribute to autism.
Some findings should be interpreted with caution, says one doctor
“It’s not the first time we’re learning this,” Anagnostou said. “We have lots of evidence from animal-model and previous human studies that significant infection during pregnancy increases risk for neurodevelopmental disorders, including autism.”
However, there are a few findings that should be interpreted with caution, Anagnostou told Global News.
“(Researchers) tried to look at the severity of infection and whether the severity of the infection would change the impact, and… they said that severe infections were not different than a regular urinary infection, but we have to be careful because these people were admitted to hospital.”
For Anagnostou, those admitted to hospital didn’t have a “regular” urinary infection. Only a more severe infection would warrant a hospital stay. In a similar vein, the kids who later developed autism were also hospitalized.
“Both the people who had infection and the kids who had autism were hospitalized, so they are not representative of the larger population,” she noted.
Other factors which can increase your risk of autism
The most robust explanation for autism comes from our genetics, Anagnostou said.
“But our genes and our environment interact… and there’s a series of these environmental exposures that have small but consistent effects.”
One is infection during pregnancy, and some infections are worse than others.
“That’s why we want all moms to be vaccinated. For example, rubella during pregnancy (is linked with) a very high risk of autism.”
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“Other factors could be maternal diabetes, use of certain medications during pregnancy, an increased paternal age… all of these things are robust. We know they’re important to biology, but the actual increase is very small for each one of them… so no parent should be feeling guilt because they happen to develop an infection during pregnancy,” said Anagnostou.
“We have zero evidence that vaccines increase the risk for autism.”
Autism is a difference that comes with both “difficulties and advantages”
According to Anagnostou, autism is a developmental difference that causes the brain and the body to grow and connect in different ways than someone who doesn’t have autism.
“Sometimes, that’s associated with things that cause distress and dysfunction, and we want to treat those things,” said Anagnostou. “But sometimes, it actually comes with unique gifts and unique perspectives.”
Anagnostou said people with autism are more likely to think out of the box and they’re more likely to contribute to innovation.
“Speaking generally, they’re good employees, they have very low absenteeism (rates), they tend not to lie,” Anagnostou explained. “It’s a difference that comes with both difficulties and advantages.
“It’s important that we don’t lose perspective of the things that need to be treated, because a lot of these children need our support, but it’s also important to not lose perspective of all the unique qualities people with autism bring to society.”