It's unclear just how many children born prematurely will develop autism. The study, in the November issue of Pediatrics, included 1216 children with autistic disorders and 6080 without.
When Dr. Susanne Buchmayer and colleagues from the Karolinska Institute, Stockholm, took various factors into account, children who were born at 31 weeks of pregnancy or earlier were about 1.5 times as likely to develop autism compared to babies born at full term. Those born from 32 to 36 weeks were about 1.3 times as likely to develop the condition.
However, when they took complications of pregnancy and early life into account, there were no significant differences between babies born at 36 weeks and earlier and those born later, suggesting that the complications themselves, and not the prematurity, were the link.
For example, preeclampsia - a life-threatening condition marked by high blood pressure, fluid retention and protein in urine -- was associated with greater than 50% increased risk of an autistic disorder in children.
Other complications linked to an increased risk: babies born small for the length of pregnancy, low infant blood sugar, birth defects, and infant seizures.
The also authors point out that the majority of children with autism were born at term, and call for research into whether preventing the complications of birth could prevent the disorder.