Prematurity seems to be a significant risk factor for developing autism. About 13% of all births are premature, although these stats vary by higher- vs. lower-income countries. In higher-income countries, approximately 9% of babies are born premature .
Because preemies’ organs are developmentally immature for the demands of their ex utero lives, they are prone to respiratory distress due to low levels of lung surfactant. They are also prone to necrotizing enterocolitis due to poor blood supply to the GI tract, a condition in which parts of the bowel may die off. And finally, they are prone to intraventricular bleeds in the brain. These bleeds are more likely to occur the more extreme the prematurity. Infants with grades III-IV (more extreme) intraventricular hemorrhages are also most likely to develop cerebral palsy.
As I’ve discussed before, autism shares a strong link with prematurity, and the more extreme the prematurity, the stronger the link. However, research suggests that prematurity per se may not be the primary risk factor but the extent of intracranial bleeds.
In fact, researchers have found that infants who have intraventricular bleeds that lead to enlargement of the ventricles have almost a 7 fold higher risk for autism than preemies who have normal cranial ultrasounds.
Presumably major intraventricular bleeds damage the surrounding tissues due to increased pressure, and this damage may be key in the development of autism. How this these vents predispose towards autism is still not well understood, although damage likely results in a loss of functional brain tissue.