Date Published: May 27, 2021
Children who were born prematurely are much more likely to be diagnosed with autism than children who were born on time, according to research.
In a large analysis, researchers found that 7 percent of premature babies were later diagnosed with autism.1 That’s significantly higher that the U.S. autism rate of 1.8 percent of children. The researchers, who were based in Australia, analyzed the results of 18 scientific studies that included 3,366 premature and low-birthweight babies in various countries.
Premature, or preterm, birth increases the risk of medical complications and death. The earlier a baby is born, especially before 32 weeks, the greater the chance of breathing, developmental, vision, or hearing problems, according to the U.S. Centers for Disease Control and Prevention (CDC). The average pregnancy is 40 weeks long. A premature baby, or preemie, is born before 37 weeks.
The link between prematurity and autism does not mean that one necessarily causes the other.
“The two may be seen together but caused by another factor, such as a gene abnormality,” says Paul H. Lipkin, M.D., a pediatric neurodevelopmental specialist and director of medical outpatient services at Kennedy Krieger Institute in Maryland. “Is a gene abnormality causing preterm birth; is it causing the neurodevelopmental problems seen in autism?” asks Lipkin, who was not involved in that study.
Genes and other factors may contribute to autism, together or separately. The stress of prematurity on a developing baby’s brain may work together with a “biological vulnerability” to increase the likelihood of autism in some children, according to the Australian researchers’ study.1
A different study of prematurity and autism found that the autism rate increased for each additional week that a baby was premature.2 For example, almost 23 percent of the children born at 25 weeks received an autism diagnosis, compared with 6 percent of the children born at 31 weeks, according to those researchers. This tended to happen more in girls.
That research team studied 416 preemies who were born in Israel and followed for 2 to 14 years. Eventually, 43 children, or 10 percent, received an autism diagnosis. The autism group had a higher percentage of girls than typically found in autism studies.
In 2019, 1 in 10 babies were born prematurely in the United States, according to the CDC. Being pregnant with twins or multiple babies, having a history of premature delivery, pregnancy complications, smoking, and substance use each increase the risk of an early delivery. But some mothers give birth prematurely even when none of these factors apply to them. Researchers are interested in possible genetic and environmental factors that affect preterm birth.3
About 12 percent of SPARK research participants who have autism were preemies, according to information they or their parents shared. Almost one-fifth of that group was very premature, having been born at 31 weeks or earlier.
Other pregnancy-related factors may contribute to the chance of a child having autism. These factors include having older parents, prenatal exposure to some pesticides or air pollution, very low birth weight, birth complications, and a mother’s diabetes, immune system problems, or obesity during pregnancy, according to the National Institute of Environmental Health Sciences (NIEHS). “But these factors alone are unlikely to cause autism. Rather, they appear to increase a child’s risk for developing autism when combined with genetic factors,” NIEHS says.
Read “The Preemie with a Fighting Spirit” about a SPARK participant who was born at 27 weeks.