Understanding Autism Risk: What Science Really Says.
Dr. Brian R. Lopez, PhD, BCBA | Article | April 13, 2026
Summary
In this post, Dr. Brian R. Lopez, PhD, BCBA, draws on more than 25 years of clinical experience to explain what modern science knows about the causes of autism and why diagnoses have increased. Autism is not caused by parenting or vaccines—it results from a complex combination of genetic and prenatal factors that shape brain development in different ways for each person. While genetics account for most of the risk, early identification and access to behavioral interventions make the greatest difference in quality of life. The rise in autism diagnoses reflects better awareness, improved screening, and expanded access to services—not a new cause. Dr. Lopez encourages families to focus on early screening and evidence-based supports to help every child reach their full potential.
Families often ask for clear, science-based answers about autism:
What increases risk? What doesn’t? Why do we hear that autism rates are rising?
This post summarizes what the strongest research shows — in plain language — along with practical numbers families can use and guidance on early screening.
Known Risk Factors: What the Numbers Really Mean
1. Sibling Recurrence
Younger siblings of autistic children have a higher chance of being diagnosed themselves.
- About 20% of younger siblings receive an autism diagnosis by age 3.
- The risk is higher when more than one older sibling is autistic and slightly higher for boys.
- Even when not diagnosed with autism, many high-risk siblings show language or developmental delays and benefit from early support.
2. Advanced Parental Age
Research shows a small but consistent increase in autism risk with parental age:
- For mothers, risk rises by about 18% for every 10-year increase.
- For fathers, it rises about 21% per decade.
- In the oldest age groups, overall risk is roughly 40–50% higher than average.
3. Valproate (Depakote) Use During Pregnancy
Valproic acid, a medication used to treat seizures and bipolar disorder, is a well-documented risk factor.
- Large national studies estimate an absolute risk of about 4.4% for autism in children exposed during pregnancy.
- The relative risk is nearly three times higher than in unexposed pregnancies.
- Medical guidelines strongly recommend avoiding valproate in pregnancy when possible.
4. Very Preterm Birth
Babies born very early, especially before 32 weeks, have a higher likelihood of autism compared to full-term peers. This link is consistent across large national and international cohorts.
In short: Genetics explains most autism risk, but factors such as sibling recurrence, valproate exposure, parental age, and prematurity have measurable and consistent effects. The first two — sibling recurrence and valproate — are the most useful for clinical counseling.
What We Know Is Not a Cause
There are a few topics that spread widely online but are not supported by credible science.
Vaccines (Including MMR)
Dozens of large national studies and meta-analyses have confirmed:
Vaccines do not cause autism.
The single 1998 paper that suggested a link between the measles, mumps, and rubella (MMR) vaccine and autism was retracted in 2010 due to serious ethical and methodological flaws. This has been tested repeatedly since, the answer remains the same.
Tylenol (Acetaminophen) During Pregnancy
This topic often circulates on social media, but the evidence doesn’t support a causal connection. Some observational studies have found weak associations, but more rigorous sibling comparison studies do not.
Professional groups such as the American College of Obstetricians and Gynecologists (ACOG) continue to advise that acetaminophen can be used in pregnancy when clinically needed and at the lowest effective dose.
Summary: Neither vaccines nor acetaminophen cause autism. These myths persist because they sound simple — but the science is clear and consistent.
Early Screening: Why Timing Matters So Much
Early identification opens doors to effective supports. The American Academy of Pediatrics recommends autism screening at 18 and 24 months, along with ongoing developmental surveillance.
Validated tools like the M-CHAT-R/F (Modified Checklist for Autism in Toddlers, Revised with Follow-Up) help primary care providers decide when a full evaluation is needed.
Earlier Screening for High-Risk Families
If you already have an autistic child, your next child has higher odds, about 20%, of also being on the spectrum. For these families, screening can start even earlier, often around 10–12 months.
Telehealth-based screening can be especially valuable for high-risk families: it allows a clinician to observe early social attention, imitation, play, and communication in a familiar home setting — often providing a clearer picture of development than brief clinic visits.
If you’re concerned about your infant or toddler’s social engagement, language, or play, don’t wait. You can talk with our Care Team to explore whether a full evaluation is the right next step for your family.
Why Autism Diagnoses Have Increased — and What It Really Means
As a clinician, I’ve seen the steady rise in autism diagnoses over the past two decades. The increase doesn’t reflect a sudden change in biology or environment, it reflects how we identify and support people today.
Here are 10 clear reasons the numbers have risen:
| No. | Driver | What Changed | What It Does |
|---|---|---|---|
| 1 | DSM-5 Spectrum (2013) | Combined multiple labels into one autism spectrum | Fewer missed diagnoses, more consistency |
| 2 | Primary Care Screening | Routine screening at 18 and 24 months | Earlier referrals |
| 3 | Earlier Identification | More diagnoses by age 4 in newer birth cohorts | Detects autism sooner |
| 4 | Greater Awareness | Families and educators recognize signs earlier | More evaluations |
| 5 | Insurance Mandates | State laws expanded autism coverage | More children receive diagnosis and services |
| 6 | School Coding Changes | Diagnostic substitution from "intellectual disability" to autism | Numbers shift categories |
| 7 | More Providers | Growth in specialists and clinics | Improved access, shorter waits |
| 8 | Equity Efforts | Better identification among girls and underrepresented groups | Reduces underdiagnosis |
| 9 | Telehealth Access | Remote evaluations and screenings | Reaches rural and busy families |
| 10 | CDC Surveillance Expansion | More monitoring sites, better methods | More accurate community counts |
In 2022, the CDC’s Autism and Developmental Disabilities Monitoring (ADDM) Network estimated that 1 in 31 8-year-olds met criteria for autism across 16 U.S. sites.
Bottom line: Rising numbers reflect progress in awareness, access, and inclusion, not a new environmental cause.
Where Our Energy Should Go Next
Research into autism’s causes remains valuable, especially for identifying preventable risks like valproate exposure and improving genetic understanding.
But the greatest need is not discovering new risk factors, it’s supporting people who are autistic today.
That means fully funding:
- Early intervention and special education
- Evidence-based behavioral and developmental therapies
- Communication systems and vocational programs
- Mental health care and sensory-friendly environments
- Adult services and independent living options
Decades of research show that comprehensive behavioral interventions yield the strongest improvements in skills and quality of life. Our collective focus should be on access, equity, and lifelong support.
If You’re Concerned About Your Child
If your child is between 10 and 24 months old, has an older autistic sibling, or shows early signs such as:
- Limited eye contact
- Little response to name
- Few gestures or loss of words
- Repetitive or unusual play
- Strong sensory reactions
…it’s time to reach out.
A brief conversation with our Care Team can help you understand what a comprehensive diagnostic evaluation involves — so you can decide whether it’s the right next step for your family.
Early identification opens the door to supports that help your child grow, learn, and thrive.