A new study that combines data from over 20 million births has claimed that a caesarean section delivery is associated with autism spectrum disorder (autism) and attention-deficit hyperactivity disorder (ADHD).

The research from Sweden published in the journal JAMA Network Open linked caesarean births with neurodevelopmental disorders, specifically a 33 per cent higher chance of autism.

The report said:

"In this systematic review and meta-analysis of 61 studies comprising more than 20 million deliveries, birth by caesarean delivery was significantly associated with autism spectrum disorder and attention-deficit/hyperactivity disorder."

But obstetrician, Dr Alex Polyakov says the study is weak and urges people to take it cautiously.

"The statistical analysis that was performed in this research may have shown an association. It does not mean that the caesarean section is the cause of the disease," he says.

Queensland obstetrician Gino Pecoraro backs this sentiment and urges people to not be alarmed by the research.

"Unfortunately what sounds like a good scientific study does not really help the situation but just creates anxiety and panic," he says.

"This study is certainly interesting and begs further prospective research be undertaken to try and answer the question of whether delivery by caesarean section increases the burden of mental health issues in children.

Ultimately, this study does not answer this question, but merely comes up with the correct recommendation that 'further research is required'."

Gino says this research should not affect a woman's decision to have a c-section.

"This shouldn't put women off having a caesarean section if they need to have one," he says.

Caesarean sections are common, with one in three Australians born this way.

It can be a lifesaving intervention for women with complicated pregnancies and births.

One in three Australians are born via c-section.

What is autism?

According to Autism Spectrum Australia, 1 in 70 Australians are diagnosed with autism spectrum disorder.

The word spectrum reflects the wide range of difference that people on the spectrum experience and the extent to which they may be affected. No two people on the autism spectrum are alike, and all have unique strengths and interests.

All people on the autism spectrum are affected to some degree in two main areas: social communication and repetitive patterns of behaviour. Autism is also often characterised by sensory sensitivities. Autism is a lifelong developmental condition.

• Characteristics of Autism Spectrum Disorder (ASD) can include:

• Language – absent, delayed or abnormal patterns

• Play – isolated, repetitive, a preference for predictable play, difficulty with flexible thinking

• Body movements – behaviour such as flapping and toe walking, and other behaviours that may cause self-injury, such as hand biting

• Tantrums – in a bid to express extreme confusion, stress, anxiety, anger and frustration when unable to express their emotions

• Sensory sensitivities – to certain sounds, colours, tastes, smells and textures

What is ADHD?

ADHD is a term used to describe a neurodevelopmental disorder with a recognised and persistent pattern of behaviour. It is thought to be an inherited genetic disorder.

A neurodevelopmental disorder is a condition which usually manifests early in a child's development, often before the child enters primary school, and are characterised by developmental deficits that produce impairments of personal, social, academic, or occupational functioning.

ADHD is characterised by developmentally inappropriate levels of inattention, impulsivity, and hyperactivity.

Key features of ADHD are:

• Inattention

• Distractibility

• Hyperactivity

• Impulsivity