A virus common in newborn babies may increase their risk of developing autism, a study suggests. 

By examining medical records of nearly 3million infants, researchers found those born with cytomegalovirus (CMV) were two-and-a-half times more likely to be diagnosed with autism in their lives than children without CMV. 

This seemingly harmless cold-like bug affects roughly one in every 200 babies, and is the most common infection present at birth in the US.

Yet doctors don't currently screen for the common virus, which is passed from pregnant women to their fetus in the womb.

Researchers believe the illness may cause inflammation in the fetus' brain that interrupts its development, causing symptoms associated with autism, said Dr Megan Pesch, the study's lead author.

The pediatrician, at the University of Michigan, told DailyMail.com that her daughter was born with CMV and was later diagnosed with autism, despite appearing perfectly healthy at birth. 

She wants to raise awareness about the virus, so that screening during pregnancy might become more common in the US, as it is in other countries. 

This might allow more research into the topic to determine what CMV causes, 'to better understand what congenital CMV comes with so we can better support families.' 

Some studies suggest babies born with the virus are at higher risk of developing other symptoms - like hearing loss and developmental delays. 

Approximately 2.8 percent of American children are diagnosed with autism.

Researchers don't know what causes the condition.

It's thought that genetics might play a role - but so too can injury or other environmental factors. 

Autism results in a host of behaviors, but generally is defined as a condition that affects how people interact, communicate and learn.

Some common symptoms include sensitivity to noises, difficulties interpreting social cues and a delayed language skills.

Most children don't get diagnosed until after age three, according to the NIH. 

Usually, CMV is relatively harmless, and you probably wouldn't even realize your child has it, since many have no symptoms. 

Dr Pesch said some studies suggest up to 90 percent of cases at birth may therefore go undiagnosed. 

It's contracted when someone comes into contact with the saliva of an infected person. 

It's particularly common in toddlers, Dr Pesch said, so she recommends that pregnant women and their partners avoid contact by washing hands frequently.

When a mother gets infected with CMV while pregnant, it's able to pass through the placenta and infect the child. 

This causes inflammation in the fetus' brain. The theory is that inflammation can put pressure on the fragile, developing brain tissue, in turn interrupting normal development and increasing the likelihood of developing autism. 

There are some IV infusions or pills that doctors can give patients diagnosed with CMV - but they reserve those for people with poor immune systems and newborns, and tend not to give it to pregnant people in the US. 

When children do have symptoms, it's similar to a cold - including swollen lymph nodes and a sore throat. 

In about 20 percent of cases, a newborn can develop birth defects or other long term health problems from congenital CMV - like epilepsy, hearing loss or cerebral palsy. 

In her study published in the journal of the American Academy of Pediatrics, Dr Pesch analyzed the insurance claims of around 3 million children through Medicaid or Children's Health Insurance Program. 

Doing so, they found that  baby girls born with CMV were more than four and half times more likely to develop autism than those without it. 

Boys born with CMV were two times more likely to develop autism than those without it. 

Overall the risk across both sexes was two-and-a-half times greater among kids born with CMV. 

In other countries, antivirals are regularly given to treat CMV during pregnancy, and Dr Pesch said its similar to the medication used to treat genital herpes, and is likely harmless. 

Dr Pesch suggests that earlier screening for the virus - when babies are still in the womb - could give doctors a chance at stopping CMV before it harms the child's brain. 

Even making screening at birth standard could help, she said, cluing in new parents for their child's higher risk of developing hearing problems and autism. 

In states like Connecticut, Florida and Kentucky - newborns are already screened for CMV. But she hopes that the US will follow the example of their neighbors to the north - Canada has already implemented pre-birth CMV screenings. 

'If you know that these kids might be at a higher risk for autism you can provide these families with like services and support and watch for symptoms earlier,' Dr Pesch said. 

'I think everyone would agree that kids with autism can benefit from some earlier support, not to change them not to, like, cure them, you know, we don't want that but to like, help them develop language navigate the world.'