MUMS who rush to get pregnant again shortly after giving birth are 50 per cent more likely to have a child with autism, experts have warned.
Those who wait too long between kids face the same risk.
Children conceived between 18 months and five years after a previous birth are less likely to suffer from the developmental condition.
Experts say women may be unable to replenish their body with the nutrients a foetus needs if they fail to wait long enough between pregnancies.
And a long gap may indicate underlying fertility issues, which is an established risk factor.
The Centers for Disease and Control Prevention, in Atlanta, US, analysed data on 356 children with autism spectrum disorder and 524 without.
Kids conceived very soon after a sibling was born were twice as likely to have severe autism than those born within the 18 months to five year time frame.
And those conceived a long time after a sibling was 1.8 times more likely to be severely autistic.
Autism is a lifelong, developmental disability that affects how a person communicates with and relates to other people, and how they experience the world around them.
Around 700,000 people are on the autism spectrum in the UK, which is around 1 per cent of the population.