Cerebral palsy is not always caused at birth. While birth complications are a well-known risk factor, the brain damage behind most cases actually occurs before labor begins. A smaller number of cases develop after birth, during infancy or early childhood. Understanding when and how these injuries happen helps clarify why cerebral palsy is far more complex than a single birth event.
Most Cases Begin Before Birth
The majority of cerebral palsy cases trace back to problems that develop during pregnancy, long before labor starts. The developing brain is vulnerable to a range of prenatal insults, and disruptions during critical growth periods can cause the kind of lasting damage that leads to cerebral palsy.
Infections during pregnancy are one of the most established prenatal risk factors. When a pregnant person contracts certain infections, the immune response floods the baby’s brain and blood with inflammatory proteins called cytokines. These proteins can damage developing brain tissue directly. Viruses linked to cerebral palsy include chickenpox, rubella (German measles), and cytomegalovirus (CMV). Bacterial infections of the placenta, fetal membranes, or maternal pelvic area also raise the risk.
Premature birth is another major prenatal pathway. Babies born before 37 weeks of gestation have immature brains that are especially vulnerable to injury. The white matter, which carries signals between brain regions, is particularly fragile in preterm infants. Bleeding inside the brain (intraventricular hemorrhage), inflammation, and oxygen deprivation can all damage this white matter and disrupt normal cortical development. The earlier a baby is born, the higher the risk.
What Happens During Birth
Birth complications do cause some cases of cerebral palsy, but the proportion is smaller than many people assume. The idea that oxygen deprivation during delivery is the primary cause of cerebral palsy is deeply embedded in popular understanding, yet research paints a more nuanced picture. Across 23 studies examining the link between birth asphyxia and cerebral palsy, the proportion of cases attributed to oxygen loss during delivery ranged from less than 3% to over 50%, depending on how “birth asphyxia” was defined. That enormous range reflects how difficult it is to pin a case of cerebral palsy on a single moment during labor.
That said, serious birth complications can and do cause brain injury. Prolonged oxygen deprivation during labor, often called hypoxic-ischemic encephalopathy, is the most recognized birth-related cause. This can happen when the umbilical cord is compressed, the placenta separates too early (placental abruption), or labor is severely prolonged. When the brain is starved of oxygen for long enough, neurons begin to die, and the resulting damage can produce the motor impairments characteristic of cerebral palsy.
For babies who do experience significant oxygen deprivation at birth, a treatment called therapeutic hypothermia (brain cooling) can reduce the severity of injury if started quickly. The baby’s body temperature is lowered to about 33 to 34 degrees Celsius for 72 hours. This slows the cascade of brain cell death that follows oxygen loss. Whole-body cooling reduces the odds of developing cerebral palsy by roughly 30 to 40% compared to standard care, and it also lowers the risk of death and neurodevelopmental delay at 18 months. The treatment needs to begin within the first six hours of life to be most effective.
Cerebral Palsy Can Also Develop After Birth
A small number of children develop what’s called acquired cerebral palsy, meaning the brain injury occurs more than 28 days after birth. The causes are distinct from prenatal and birth-related factors and typically involve a clear event during infancy or early childhood.
Brain infections like meningitis and encephalitis can cause severe inflammation and permanent damage. Strokes, which can occur even in infants due to blood clotting problems, abnormal blood vessels, sickle cell disease, or heart defects present at birth, are another cause. Head injuries from car accidents, falls, or child abuse round out the list of postnatal causes. While acquired cerebral palsy accounts for a minority of all cases, it’s a reminder that the window of vulnerability extends well beyond delivery.
Genetics Play a Larger Role Than Once Thought
For decades, cerebral palsy was understood almost entirely as the result of environmental injury: an infection, a lack of oxygen, a traumatic event. That picture is shifting. Researchers have found that spontaneous genetic mutations, ones that appear in the child but aren’t inherited from either parent, can directly cause cerebral palsy. These “de novo” mutations disrupt genes involved in brain development and have been identified in multiple cases where no obvious environmental cause was present.
Beyond single-gene mutations, a 2021 genome-wide study of over 600 people with spastic cerebral palsy (the most common type) found that many common genetic variants, each with a small effect, may collectively increase risk. This supports the idea that cerebral palsy can be a polygenic condition, caused by the combined influence of multiple genes rather than a single mutation.
Perhaps most interesting is the emerging view that genetics and environment interact. Certain genetic variants may make a developing brain more susceptible to the same insults, like infection or oxygen loss, that another baby’s brain would weather without lasting damage. Two babies exposed to the same stressor during pregnancy or birth might have very different outcomes depending on their genetic makeup. This helps explain why many babies experience difficult births without developing cerebral palsy, while some with seemingly uncomplicated deliveries do.
When Cerebral Palsy Is Diagnosed
Regardless of when the brain injury occurs, cerebral palsy is generally diagnosed during the first or second year of life. The condition affects movement and muscle coordination, and these problems become more visible as a child reaches developmental milestones. By 9 months, many movement issues are noticeable. Mild delays may become clearer around 18 months. By 24 to 30 months, most movement delays can be identified. In cases where symptoms are subtle, a confirmed diagnosis may take a few years longer.
This gap between when the brain injury happens and when the diagnosis is made adds to the confusion about causes. Parents often look back at the birth for an explanation, even when the injury may have occurred weeks or months earlier during pregnancy, or after birth during a childhood illness. The truth is that cerebral palsy has no single cause and no single moment of origin. It’s the result of brain damage that can happen at many different points, from early pregnancy through infancy, through a wide variety of mechanisms.