How does autism vs Down syndrome risk compare with advanced parental age?

PostedDecember 2, 2025

UpdatedDecember 2, 2025

ByMy Patient Advice

Author: Hannah Smith, MSc | Reviewed by: Dr. Rebecca Fernandez, MBBS

When discussing autism vs Down syndrome risk, it is important to understand how advanced parental age affects the likelihood of both conditions. While both autism and Down syndrome risk increase with age, the magnitude of risk differs considerably.

Autism vs Down syndrome risk varies significantly, with Down syndrome showing a sharper and more predictable rise with maternal age, while autism risk increases more modestly. For example, the absolute autism vs Down syndrome risk for mothers over 40 is higher for Down syndrome, with the risk reaching approximately 1 in 84 at age 40, compared with 1 in 100 or higher for autism. However, although autism risk does rise with age, it still remains relatively low.

Comparing the two risks

Here’s how autism vs Down syndrome risk plays out for older parents:

Down syndrome risk increases sharply

For mothers over 40, the risk of having a child with Down syndrome rises significantly, increasing from around 1 in 1,000 at age 30 to 1 in 84 by age 40.

Autism risk increases more modestly

For autism, advanced parental age typically raises the relative risk by 40-50% for mothers over 40, but the absolute risk remains lower in comparison, at around 1 in 100 or 1 in 200, depending on specific population studies.

Genetic conditions comparison

The genetic conditions comparison highlights that while Down syndrome is strongly and directly tied to maternal age, autism is influenced by a mixture of genetic and environmental factors. Therefore, while prenatal risk statistics show a moderate increase in autism risk, it is not nearly as dramatic as the rise in Down syndrome risk.

Visit providers like Autism Detect for personalised consultations that provide context around both autism vs Down syndrome risk, supporting informed prenatal risk statistics discussions grounded in clinical guidance on autism principles.

For a deeper dive into the science, diagnostic nuances, and full developmental outlook, read our complete guide to Advanced Parental Age.

Hannah Smith, MSc

Author

Hannah Smith is a clinical psychologist with a Master’s in Clinical Psychology and over three years of experience in behaviour therapy, special education, and inclusive practices. She specialises in Applied Behavior Analysis (ABA), Cognitive Behavioural Therapy (CBT), and inclusive education strategies. Hannah has worked extensively with children and adults with Autism Spectrum Disorder (ASD), ADHD, Down syndrome, and intellectual disabilities, delivering evidence-based interventions to support development, mental health, and well-being.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the author's privacy.

Dr. Rebecca Fernandez, MBBS

Reviewer

Dr. Rebecca Fernandez is a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence-based approaches such as CBT, ACT, and mindfulness-based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well-being.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the reviewer's privacy.