Washington - A US study out this week has found that pregnant women who take drugs to speed up their labour may have a higher risk of bearing children with autism.
The study in Jama Pediatrics is the largest of its kind on the matter, but stops short of stating that induced labour is a cause of the developmental disorder which affects as many as one in 88 children in the United States.
Instead, it points to the need for more research, said senior author Marie Lynn Miranda, dean of the University of Michigan School of Natural Resources and Environment.
"The scientific community has long looked for environmental contributors to the rising rates of autism in the United States," she said in a statement.
"This study provides preliminary evidence of an association between autism and labour induction/augmentation, especially among male children."
The study examined records for 625 000 births in the state of North Carolina over an eight-year period, and found that labour that was both induced and augmented was associated with a 35% higher risk of autism in boys, compared with labour that received neither treatment.
A small increased risk was seen in girls born to mothers who had induced, but not augmented, labour.
Women may have their labour induced with drugs for a number of reasons, including a baby past its due date, or medical conditions like an infection, high blood pressure or diabetes.
Researchers said the higher risk linked to induction was similar to that seen in other known risk factors for autism, such as being an older mother or giving birth before 34 weeks.
Michael Rosanoff, associate director of public health research at Autism Speaks, said the "next step is for research to better understand the possible mechanisms behind this relationship".
He added: "It is important to note that this study does not demonstrate a causal relationship between induced or augmented childbirth and autism, and that both have been shown to prevent complications during labour."