What causes autism during pregnancy?

Autism spectrum disorder (ASD) is a neurodevelopmental condition that can affect how a child communicates, interacts with others, and experiences the world around them. While autism is usually diagnosed in early childhood, it actually begins much earlier - during those crucial stages of brain development in pregnancy.

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One of the biggest misconceptions about autism is that there’s a single cause. But research shows it’s not that simple. Instead, autism is thought to develop through a mix of different factors – like genetics, environmental influences, and maternal health. No one thing can fully explain why some children are diagnosed and others aren’t.

For parents wondering if something they did during pregnancy caused their child’s autism, the answer is no.

Autism is not the result of poor prenatal care, diet choices, or a single medication. Instead, scientists believe that a combination of genetic conditions, pregnancy-related factors, and environmental exposures may increase a child’s risk. But even then, having these risk factors doesn’t mean a child will be autistic. In fact, many children exposed to the same things aren’t diagnosed at all.

This article explores how autism develops, what research suggests about pregnancy-related and environmental risk factors, and what expectant mothers can do to support a healthy pregnancy.

How does autism develop?

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Autism develops as the brain forms and grows, starting in the earliest stages of fetal development.

Scientists believe that autism spectrum disorder results from a mix of genetic and environmental factors that influence neurological development before birth.

While every autistic person is unique, research suggests that autism affects how different areas of the brain communicate with each other.

The role of genetics

Genetic factors play a major role in how autism develops. While there isn’t one specific gene that causes autism, researchers have identified a number of genetic variants and mutations that may contribute to a diagnosis.

We also know that autism can run in families. Children with a family history of autism – or other neurodevelopmental conditions like fragile X syndrome or ADHD – may have a higher likelihood of being diagnosed themselves.

Prenatal genetic testing can screen for certain conditions during pregnancy, such as Down syndrome, but it can’t currently detect autism before birth. However, ongoing research continues to shed light on the genetic links behind autism, helping us better understand the many factors that may be involved.

Brain development in the womb

The brain develops rapidly during pregnancy, with billions of neurons forming in just the first trimester.

Scientists believe that autism may begin during this critical period when certain brain cells grow or connect differently than usual.

Areas of the brain responsible for social communication, sensory stimuli processing, and emotional regulation may develop uniquely in autistic people.

The influence of prenatal and environmental factors

While genetics lay much of the groundwork, they’re not the only factor at play. Environmental influences during pregnancy, like maternal infections, age, or exposure to certain toxins, may slightly increase the chances of a child being diagnosed with autism.

But it’s important to remember: these factors alone don’t cause autism. Many children exposed to the same conditions are not autistic. What the research suggests is that autism likely develops through a mix of genetic and environmental influences, rather than any single cause.

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Pregnancy-related risk factors for autism

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While autism spectrum disorder is primarily influenced by genetics, certain pregnancy-related factors have been linked to an increased risk of autism. Again, we have to emphasise that correlation does not necessarily mean causation. These factors don’t guarantee an autism diagnosis for your little one.

Maternal health conditions

Certain maternal health conditions during pregnancy may impact fetal brain development and contribute to an autism diagnosis. These include:

Gestational diabetes
Some studies have found a possible link between gestational diabetes and a higher likelihood of autism. Researchers believe this may be due to the way gestational diabetes can affect brain development in the womb.

High blood pressure (preeclampsia)
Conditions like preeclampsia may impact blood and oxygen flow to the developing baby, which could influence how the brain forms and functions.

Maternal infection
Viral or bacterial infections during pregnancy. especially in the first or second trimester, may play a role in shaping the developing brain. Some research points to the body’s immune response during infection as a possible factor in increased autism risk, though more studies are needed to fully understand this link.

Pregnancy and birth complications

Some complications during pregnancy and delivery have been explored for their possible connection to autism, including:

Preterm birth
Babies born before 37 weeks may have a slightly higher chance of being diagnosed with autism, possibly due to the way premature birth can affect brain development.

Low birth weight
Some studies suggest that babies with lower birth weight might be at increased risk, although the exact reasons aren’t yet fully understood.

Oxygen deprivation during birth (perinatal hypoxia)
A reduced oxygen supply during labour or delivery has been associated with a higher likelihood of neurodevelopmental differences, including autism.

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Possible environmental risk factors for autism during pregnancy

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Researchers have also examined how environmental exposures during pregnancy might contribute to autism risk. While no single factor has been proven to cause autism, some studies suggest that long-term exposure to specific pollutants could have a small impact on fetal brain development.

Air pollution and toxins

Exposure to high levels of air pollution, particularly fine particulate matter (PM2.5) and traffic-related pollutants has been linked to a slightly increased risk of autism. Some studies suggest that prolonged exposure during pregnancy could affect fetal development, but more research is needed.

Other environmental toxins that have been investigated for their potential impact include:

• Heavy metals such as lead and mercury
• Pesticides used in agriculture
• Endocrine-disrupting chemicals found in plastics and household products

Maternal stress and its potential impact

Chronic stress during pregnancy has also been explored as a potential risk factor. Stress hormones like cortisol can cross the placenta and may influence how the fetal brain develops. That said, this area of research is still evolving and it’s important to remember that most pregnancies involve some level of stress, with no negative impact on the baby.

While avoiding all environmental influences is impossible, minimising exposure to known toxins where possible may support your overall health – and your baby’s too.

Medications and substances that may influence autism risk

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Some medications and substances have been studied for their potential link to autism when taken during pregnancy.

Some studies have suggested a possible connection between autism and certain medications taken during pregnancy, including:

Valproic acid

Used to treat epilepsy and bipolar disorder, valproic acid has been linked in some studies to a higher chance of autism when taken during pregnancy.

Some antidepressants

Some antidepressants – Selective serotonin reuptake inhibitors (SSRIs) have been studied for a potential link to autism, though findings remain inconclusive. However, untreated depression during pregnancy carries risks, so medication decisions should be made with medical guidance.

Please note that no medication has been proven to directly cause autism, and in many cases, the benefits of treatment outweigh any potential risks. Pregnant women should always consult their doctor before stopping or changing any prescribed medication.

Substance use during pregnancy

Alcohol and tobacco

Heavy alcohol consumption and smoking during pregnancy have been linked to various neurodevelopmental effects, though their direct link to autism remains unclear.

Illicit drugs

Some studies suggest that prenatal exposure to drugs like cocaine or opioids may influence brain development, but more research is needed on their connection to autism.

Can autism be prevented during pregnancy?

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There is no known way to prevent autism, as it is primarily influenced by genetics (you can look into prenatal genetic testing) and complex developmental factors.

However, some research suggests that certain prenatal health practices may support optimal foetal development and lower certain risks, including intellectual disabilities.

Steps to support a healthy pregnancy

Maintain regular prenatal care

Routine check-ups help monitor maternal and foetal health, allowing early intervention if needed.

Take prenatal vitamins

Folic acid, taken before and during pregnancy, has been linked to healthy brain development and may lower the risk of some neurodevelopmental conditions.

Manage maternal health conditions

Conditions like gestational diabetes and high blood pressure should be carefully monitored.

Reduce exposure to harmful substances

Avoiding smoking, excessive alcohol, and illicit drugs can support overall foetal health.

Follow medical advice on medications

Always consult a healthcare provider before stopping or changing prescribed medications during pregnancy.

Wrapping it up

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While some pregnancy-related risk factors have been identified, there’s no single known cause of autism – and no way to fully predict or prevent it.

For mums-to-be, the best thing you can do is focus on looking after your health during pregnancy. That includes keeping up with regular prenatal check-ups, managing any existing medical conditions, and following your doctor’s advice when it comes to medications or environmental exposures. But it’s important to remember: autism isn’t caused by one action or decision during pregnancy.

Rather than trying to prevent autism, the focus should be on supporting healthy pregnancies and helping parents recognise the early signs, so children diagnosed with autism or other developmental disabilities can access support as early as possible. Autistic children, like all children, thrive with the right care, understanding and encouragement. Early intervention can make a world of difference in helping them grow, learn and shine in their own unique way.

Sources

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Botelho, R. M., Silva, A. L. M., & Borbely, A. U. (2024). The Autism Spectrum Disorder and Its Possible Origins in Pregnancy. International journal of environmental research and public health, 21(3), 244.

Lu, J., Wang, Z., Liang, Y., & Yao, P. (2022). Rethinking autism: the impact of maternal risk factors on autism development. American journal of translational research, 14(2), 1136–1145.

Love, C., Sominsky, L., O’Hely, M. et al. (2024). Prenatal environmental risk factors for autism spectrum disorder and their potential mechanisms. BMC Med 22, 393.