Study Says Birth Spacing Can Impact Autism Diagnosis

Midsection of a pregnant belly

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Key Takeaways

  • A study notes that waiting at least two-and-a-half years between births may decrease the possibility of a second child receiving an autism diagnosis.
  • There are numerous other factors that can contribute to a child being identified on the autism spectrum.
  • Although autism is generally believed to be genetic, the study results show the impact other factors can have.

The Centers for Disease Control and Prevention estimates that one in 54 children has been diagnosed with autism spectrum disorder. A number of factors can contribute to the brain disorder, including older parental age, pregnancy, or birth complications. According to a new study, the length of time between births may also be a factor.

Published in Autism Research, the study notes that mothers of children with autism who wait at least two-and-a-half years to conceive again reduce the chance of their next child being born on the autism spectrum. While birth spacing alone is not enough to create any definitive outcome, it can foster greater awareness of factors that may contribute to autism.

The Study

Researchers from Curtin University and the Telethon Kids Institute gathered information from over 900,000 births in Denmark, Finland, and Sweden. The data was obtained from health and medical registries from 1998 to 2007. Investigators then followed the next time those mothers gave birth and watched the younger siblings for autism spectrum disorder until 2012.

Combing the specifics allowed them to draw parallels between the two siblings born, the emergence of autism, and the length of time between the births.

Gavin Pereira, PhD

Our research found that risk of autism spectrum disorder was lowest when there was a 30 to 39-month gap between both pregnancies. These findings are important because this result translates to about 5% to 9% of autism cases that might be avoided by optimizing birth spacing.

— Gavin Pereira, PhD

“Our research found that risk of autism spectrum disorder was lowest when there was a 30 to 39-month gap between both pregnancies,” says Gavin Pereira, PhD, a professor at the Curtin School of Population Health and lead author of the study. “These findings are important because this result translates to about 5% to 9% of autism cases that might be avoided by optimizing birth spacing.”

The results also showed that when there was only a three-month gap between the birth of the first child who was diagnosed with autism and conception, the second child was 50% more likely to be diagnosed with autism. However, waiting five years between pregnancies was associated with a 24% greater chance of diagnosis.

There were, however, aspects of the study to consider.

Jason Hangauer, PhD, NCSP

As this was an observational study, we need to be careful about drawing conclusions of causality.

— Jason Hangauer, PhD, NCSP

“As this was an observational study, we need to be careful about drawing conclusions of causality," says Jason Hangauer, PhD, NCSP, a licensed psychologist at Johns Hopkins All Children’s Hospital who specializes in diagnosis and treatment of autism spectrum disorder and other co-occurring conditions. Basically, while the amount of time between pregnancies may be related to a child being diagnosed with autism, that does not mean it causes it.

“The authors are careful to note approximately one-quarter of pregnancies are unintended,” Dr. Hangauer continues. “[They also note] other factors they did not measure, such as undiagnosed psychiatric conditions in parents, parent fertility factors, and pregnancy intention, [which] may be associated with autism spectrum disorder (ASD).”

In spite of the limitations, the findings of the study may serve as the foundation for additional research.

The Autism Spectrum

Individuals who are identified as being on the autism spectrum can have a number of symptoms. Repetitive behaviors, challenges with both spoken and unspoken communication, and difficulties with social skills can possibly be a part of what they experience.

A child can be diagnosed with the condition as early as 18 months old, though signs typically appear by the age of 3. Intervening early and understanding contributing factors can be keys to implementing more beneficial coping outcomes.

“Autism is generally regarded as a condition that arises from genetic predisposition,” Dr. Pereira says. “Our study shows that although autism spectrum disorder may be genetic, it is not completely explained by genetics. The time between pregnancies is influenced by many factors, including the biological ability to reproduce and parental decision-making among others.”

The study was not designed, however, to give specific reasons as to why the spacing may help lessen the possibility of a child being born with autism. Experts hypothesize that a smaller window of time between pregnancies may leave too little time for a mother’s body to replenish necessary nutrients. Additionally, waiting too long increases the age of the biological parents, a known contributor to a child born with autism.

Family Planning

As parents begin the family planning process, there are no shortage of factors that can impact a decision. Birth spacing can be a consideration for a number of reasons, including minimizing the potential of an autistic diagnosis.

However, once a family begins growing, the best-laid plans can often take a back seat. The most important consideration is then to provide love, support, and encouragement to your child.

What This Means For You

This study provides another piece of the puzzle of potential factors that contribute to a diagnosis of autism. While the information may be beneficial, it is important to consult your healthcare provider as you make choices regarding your pregnancies. Ultimately, make decisions that are most beneficial to you and your family, and provide a loving environment for your child.

3 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Autism Speaks. What causes autism?

  2. Pereira G, Francis RW, Gissler M, et al. Optimal interpregnancy interval in autism spectrum disorder: a multi-national study of a modifiable risk factor. Autism Res. Published online August 23, 2021. doi:10.1002/aur.2599

  3. Autism Speaks. What is autism?

By LaKeisha Fleming
LaKeisha Fleming is a prolific writer with over 20 years of experience writing for a variety of formats, from film and television scripts, to magazines articles and digital content. She has written for CNN, Tyler Perry Studios, Motherly, Atlanta Parent Magazine, Fayette Woman Magazine, and numerous others. She is passionate about parenting and family, as well as destigmatizing mental health issues. Her book, There Is No Heartbeat: From Miscarriage to Depression to Hope, is authentic, transparent, and providing hope to many.Visit her website at