According to the latest study, premature birth may give rise to autism.
Extremely preterm neonates survive at increasingly early gestation periods, thanks to the advances made in intensive care in the past decades.
They are exposed to numerous stress factors during a period critical to brain development, and it is possible that this plays a key part in the development of ASD.
In the US, about 1 in 68 children have been identified with ASD, according to the Centers for Disease Control and Prevention (CDC).
The condition is reported to occur in all racial, ethnic and socioeconomic groups, but it is almost five times more common among boys (1 in 42) than among girls (1 in 189).
ASD is generally attributed to genetic factors, even if no specific autism gene has been identified.
Of extremely preterm children, 30% developed ASD symptoms
Researchers from Karolinska Institutet and Karolinska University Hospital in Sweden examined over 100 babies who had been born extremely prematurely, in other words, before week 27, the beginning of the third trimester.
With the parents' permission, the team looked at the growth of the babies' brains using magnetic resonance imaging (MRI) during the neonate period and then screened the children for autistic features when they were 6 years old.
Almost 30% of the extremely preterm-born children had developed ASD symptoms, compared with babies who are born full-term, where the rate is 1%, suggesting that birth weight and complications can increase the risk of autism.
In addition, among children born prematurely, those who developed ASD were more likely to have had complications such as surgery during the neonatal period.
Long before signs of ASD appeared, during the neonatal period, there were observable differences between the brains of extremely preterm babies who later developed ASD and those who did not.
Among the babies who later developed ASD, diminished growth was seen in the parts of the brain involved in social contact, empathy and language acquisition. All these functions are impaired in children with autism.
Researcher Ulrika Ådén says:
"Our study shows that environmental factors can also cause autism. The brain grows best in the womb, and if the developmental environment changes too early to a life in the atmosphere, it can disrupt the organization of cerebral networks. With new therapeutic regimes to stimulate the development of such babies and avoid stress, maybe we can reduce the risk of their developing ASD."
The researchers hope that early detection of the structural alterations seen in the brain may allow the early identification and intervention of children at risk of ASD.
Medical News Today recently reported that children whose mothers take antidepressants during pregnancy are more at risk of autism.