There is no single blood test or scan that confirms cerebral palsy. It is a clinical diagnosis, meaning doctors piece together findings from physical exams, standardized movement assessments, and brain imaging to determine whether a child’s motor difficulties fit the pattern. The process typically unfolds over several well-child visits, and while cerebral palsy has traditionally been diagnosed between 12 and 24 months of age, newer assessment tools can reliably identify it before a baby’s first birthday.
Developmental Monitoring and Screening
Testing for cerebral palsy usually begins with routine checks your pediatrician already performs. At each well-child visit, the doctor tracks your child’s growth and development by asking about your concerns, updating your child’s developmental history, and watching how your child moves during the exam. This ongoing tracking is called developmental monitoring, and it is the first layer of detection.
If anything looks off, a short screening test is the next step. Some screenings are parent questionnaires, like the Ages and Stages Questionnaire, where you answer questions about what your child can and cannot do. Others are brief tasks the doctor gives directly to the child. The American Academy of Pediatrics recommends formal developmental screening at 9 months, 18 months, and 24 or 30 months. These ages are chosen deliberately: many movement issues are visible by 9 months, milder delays become clearer by 18 months, and most motor delays can be detected by 24 to 30 months.
A failed screening does not mean a child has cerebral palsy. It means the child needs a closer look through a formal evaluation.
Specialized Movement Assessments for Infants
Two tools stand out for identifying cerebral palsy early, and they work best at different ages.
General Movements Assessment (Under 5 Months)
The Prechtl General Movements Assessment is considered the best clinical tool for predicting cerebral palsy in infants younger than 5 months. It is remarkably simple: a clinician records a short video of the baby lying on their back and moving freely, then analyzes the quality of those spontaneous movements. Healthy infants produce complex, fluid movements that vary in speed, force, and direction across the arms, legs, neck, and trunk. Between 3 and 5 months, these movements shift into small, continuous “fidgety” patterns. Babies who never develop these fidgety movements have a high risk for cerebral palsy, while babies whose fidgety movements look normal almost always develop typically, even if their brain ultrasound showed earlier concerns.
The accuracy is striking. Studies report 98% sensitivity and 91% specificity, meaning the assessment catches nearly every infant who will go on to develop cerebral palsy while producing relatively few false alarms. When an abnormal General Movements result is combined with a brain MRI showing damage to motor areas, the prediction is accurate more than 95% of the time.
Hammersmith Infant Neurological Examination (2 to 24 Months)
For babies older than 5 months, the Hammersmith Infant Neurological Examination takes over as the primary standardized tool. It includes 26 scored items covering five categories: cranial nerve function, posture, movements, tone, and reflexes. The examiner observes the baby and assigns a global score. A score below 73 at 6, 9, or 12 months indicates risk for cerebral palsy. Scores below 40 are found almost exclusively in children who develop severe cerebral palsy.
The age-specific thresholds get slightly more nuanced. Scores at or below 56 at 3 months, 59 at 6 months, 62 at 9 months, and 65 at 12 months predict cerebral palsy with at least 90% sensitivity and 85% specificity. When paired with an abnormal MRI, a Hammersmith score below 73 predicts cerebral palsy about 90% of the time.
Brain Imaging
An MRI of the brain is the most informative imaging test for cerebral palsy. It does not confirm the diagnosis on its own, but it can reveal the type and timing of brain injury, which helps doctors understand the cause and anticipate what challenges a child may face.
Doctors look for three broad patterns. The first is brain maldevelopment, where the brain’s structure formed abnormally during the first or second trimester. This includes conditions where the brain’s surface folds are too few, too small, or absent. The second pattern is white matter injury, which typically arises in the early third trimester and is especially common in children born premature. Periventricular leukomalacia, a type of white matter damage near the brain’s fluid-filled chambers, is one of the most frequently seen findings. The third pattern is gray matter injury affecting deeper brain structures, which tends to occur late in pregnancy or around birth in full-term babies.
Timing matters for the MRI itself. Mild white matter damage may not show up on a scan done before the brain’s insulating coating has fully developed, and subtle injuries to deeper structures can be missed during a transition phase in the first year. Doctors sometimes repeat imaging if an early scan looks normal but clinical suspicion remains high. CT scans and cranial ultrasound are occasionally used, but MRI provides the most detailed picture.
Ruling Out Other Conditions
A core part of the diagnostic process is making sure the child’s symptoms are not caused by something else entirely. Cerebral palsy is nonprogressive, meaning the underlying brain injury does not get worse over time. Progressive neurological conditions, where a child steadily loses skills, require different treatment and must be excluded.
Doctors rule out inborn errors of metabolism through newborn screening results or additional metabolic tests. If the child’s history and MRI do not clearly point to a cause, laboratory testing can check for storage disorders that affect movement, such as Tay-Sachs disease or metachromatic leukodystrophy, and metabolic conditions involving amino acid or organic acid processing. Nerve conduction studies or electromyography may be used if a progressive condition affecting the nerves is suspected. The goal is to ensure the child is not being treated for cerebral palsy when a treatable or fundamentally different condition is responsible.
Genetic Testing
Genetic testing has become an increasingly important piece of the puzzle. Research involving over 1,800 individuals with cerebral palsy found that 27% had an identifiable genetic cause, a much higher proportion than previously assumed. Among the genes identified, 58 were classified as “actionable,” meaning the genetic finding could change how the child’s condition is managed.
Current evidence suggests genetic testing can be valuable for all patients with cerebral palsy, even when there is a clear explanation for the brain injury, such as premature birth or oxygen deprivation. A genetic variant may have made the brain more vulnerable to that injury in the first place, or it may point to associated conditions that need monitoring.
How Severity Is Classified
Once cerebral palsy is diagnosed, doctors classify its severity using the Gross Motor Function Classification System, a five-level scale. It focuses on what a child actually does in everyday settings, at home, school, and in the community, rather than what they can do under ideal conditions.
- Level I: The child walks without restrictions but may have difficulty with advanced motor skills like running or jumping.
- Level II: The child walks in most settings but may struggle with uneven surfaces, long distances, or crowded spaces.
- Level III: The child walks with a handheld assistive device indoors and uses wheeled mobility for longer distances.
- Level IV: The child uses wheeled mobility in most settings and needs physical support from others for transfers.
- Level V: The child has very limited ability to move independently, even with assistive technology.
This classification helps families and therapists set realistic goals and plan for the equipment and support a child will need.
How Early Can a Diagnosis Happen?
The gap between when cerebral palsy can be detected and when it historically has been detected is significant. In settings that have adopted the newer assessment tools, the average age of diagnosis has dropped to around 9 months, compared to roughly 17 months in the same settings before those tools were implemented. That represents an 8-month head start on targeted therapy during a period when a young brain is most adaptable.
In practice, the pathway depends on the child’s age. For a baby under 5 months with risk factors like prematurity or a complicated birth, the combination of the General Movements Assessment and a brain MRI offers the fastest, most accurate route. For an older infant, the Hammersmith Exam paired with MRI provides comparable confidence. Even without access to MRI, the Hammersmith alone is 90% predictive of cerebral palsy between 2 and 24 months, making early identification possible in a wider range of clinical settings.
Children with cerebral palsy frequently have related conditions, including seizures, intellectual disability, and vision, hearing, or speech problems. A full evaluation typically screens for these as well, because catching them early opens the door to interventions that can make a meaningful difference in a child’s daily life.