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Do autistic babies grow faster?

Autism spectrum disorder (ASD) refers to a range of conditions characterized by challenges with social skills, repetitive behaviors, speech and nonverbal communication. Autism affects information processing in the brain by altering how nerve cells and their synapses connect and organize. It’s called a “spectrum” disorder because there can be a wide variation in the type and severity of symptoms people experience.

ASD begins early in childhood and eventually affects 1 in 44 children in the United States, according to estimates from the Centers for Disease Control and Prevention (CDC). Boys are four to five times more likely to be diagnosed with autism than girls.

Some parents report differences in their baby’s growth and development as early as 6 months old. While there is limited research on growth rates in autistic infants, some studies suggest autistic babies tend to have accelerated growth in head circumference and body length compared to neurotypical infants.

In this article, we will explore the evidence on growth patterns in autistic infants and address the question: Do autistic babies grow faster?

Key Takeaways on Autistic Infant Growth

– Research indicates autistic infants tend to have accelerated growth in head circumference and body length in their first year.

– Larger head size and increased body growth may be linked to early brain overgrowth in autism.

– More studies with larger sample sizes are needed to confirm accelerated growth patterns in autistic infants.

– Not all autistic infants show accelerated growth. There is significant individual variability.

– Rapid growth does not necessarily predict autism diagnosis or severity of symptoms later in childhood.

– Environmental factors like nutrition and feeding issues can also impact growth rate.

– Growth charts specifically for autistic infants would improve monitoring of development.

Head Circumference Growth

Several studies show evidence that autistic infants tend to have larger heads and accelerated growth in head circumference (HC) compared to typical infants:

– In a study of 59 autistic infants, boys had significantly larger HC than typical boys by 6-14 months. Autistic girls also had increased HC.[1]

– A study of 84 infants found those later diagnosed with autism had increased HC growth velocity from birth to 24 months.[2]

– Autistic infants show brain overgrowth early in development. More neurons, connections, and larger brain volume may drive increased HC.[3]

– Larger HC at 6-9 months has been linked to more severe autism symptoms in early childhood.[4]

However, not all studies have found accelerated HC growth. A 2018 study of 422 infants reported no significant difference in HC growth between autistic and typical infants in the first year.[5]

More research is needed with larger sample sizes and growth curve modeling to clarify HC growth patterns in autistic infants.[2] Relying on parents to recall and report measurements retrospectively can also introduce recall bias.

Body Length Growth

In addition to head size, some studies indicate increased growth in body length among autistic infants:

– A study of 66 autistic infants found greater body length at 6-18 months compared to typical infants.[6]

– Another study reported autistic infants had longer body length through 24 months.[2]

– Accelerated body growth may be linked to early overgrowth in the brain and skeletal system.[3]

However, a large 2018 study did not find significant differences in length growth.[5] As with HC, more data is needed to confirm unusual growth patterns.

Weight Gain

Research on weight gain in autistic infants shows mixed results:

– Several studies report no significant differences in weight between autistic and typical infants.[2][5][6]

– One study found autistic infants weighed more at 6 months but not 12 or 18 months.[1]

– Another reported autistic infants were heavier through 24 months.[2]

– Differences in study methodology may contribute to inconsistent findings.

– More research with larger sample sizes is needed to clarify patterns.

Overall, findings for unusual weight gain seem less consistent than for HC and length growth. But individual differences likely play a role.

Potential Causes of Accelerated Growth

The reasons for potential accelerated growth in some autistic infants remain unclear but may involve:

– Early overgrowth of the brain. Excess neuron production and connections could drive expansion of HC and body growth.[3]

– Dysregulation in proteins that control cell growth and proliferation.[7]

– Differences in the hormonal environment during early development.[8]

– Genetic factors related to regulation of growth.[9]

– Environmental influences like nutrition, feeding issues, and gut health that affect growth.[10]

More research is needed to understand the complex interplay of biological and environmental factors that shape early development and growth in autism.

Individual Variability in Growth Patterns

While group averages may indicate a tendency toward accelerated growth in autism, there is significant variability between individual infants:

– Not all autistic infants show unusual growth trajectories.[5]

– Timing of unusual growth may differ, with some infants showing changes from 6 months and others at 12 or 18 months.[1]

– Other factors like premature birth, low birth weight, and health conditions can also affect growth.[11]

– Differences in gender, genetic background, and environment likely influence growth patterns.[12]

Generalizations about growth in autism should be avoided. More data on individual variation is needed.

Relationship to Symptom Severity

Some studies suggest a link between accelerated infant growth and severity of autism symptoms later in childhood:

– Faster HC growth from 6-12 months associated with more severe social deficits at age 3.[4]

– Increased HC at 6-9 months linked to greater autism severity at ages 2-4.[13]

– However, other studies have not found these relationships.[14]

– Rapid body growth in infancy may also relate to more severe autism features.[15]

While interesting, these findings are quite preliminary. More research is needed on how early growth tracks with later symptom severity.

Growth Monitoring in Autism

Careful monitoring of growth and development is important for all infants but especially for those at high risk for autism:

– The American Academy of Pediatrics recommends autism-specific well-child visits to screen for delays.[16]

– Accelerated or unusual growth may trigger evaluation for autism.

– However, absence of unusual growth does not rule out autism, which has variable expression.

– Growth curves and screening tools designed specifically for autistic infants could improve monitoring.

– Parent education on developmental milestones and when to seek evaluation is also critical.

Early intervention as soon as delays are detected leads to the best outcomes. So careful growth monitoring and screening are priorities.

Implications of Accelerated Growth

The potential implications of accelerated early growth in autism need more research but may include:

– Increased HC and brain size could affect development of skills and behaviors.[17]

– Autism symptoms may emerge or worsen with rapid brain growth in infancy.[18]

– Effects on social communication as neural connections rapidly reorganize.[19]

– Changed nutritional needs and feeding difficulties with accelerated growth.[20]

– Higher risk of co-occurring conditions like gastrointestinal issues.[21]

– Increased risk for bullying if physical size/growth is very divergent.[22]

– Benefits from early intervention to guide development during period of rapid change.

Long-term studies are needed to clarify how accelerated infant growth relates to developmental outcomes. This could inform strategies to improve prognosis.

Key Things for Parents to Know

For parents concerned about their baby’s development and growth, keep these points in mind:

– Unusual growth patterns may indicate risk for autism, but many autistic infants grow typically.

– Accelerated growth does not necessarily mean more severe autism. Outcomes vary.

– Pay attention to developmental milestones like eye contact, babbling, and smiling, not just growth charts.

– Make sure your baby has regular checkups and autism-specific screening.

– Don’t delay evaluation and early intervention if you have any concerns. Waiting reduces benefits.

– Work closely with your pediatrician to monitor growth and development carefully during infancy.

– Reach out for support services like speech therapy, occupational therapy, and feeding assistance if needed.

– Connect with other parents going through similar experiences. You are not alone!


Some research suggests autistic infants may show accelerated growth in head size and body length compared to typical infants in the first year of life. This seems linked to early brain overgrowth. However, findings are mixed, and significant individual variability exists. More studies are needed to clarify growth patterns and their relationship to developmental outcomes in autistic children. Careful monitoring of growth and milestone achievement is essential to support early intervention and improve prognosis. While findings remain preliminary, investigating unusual growth trajectories may yield insights into the biological basis of autism and potential targets for future treatments.