As advances in medicine and discoveries in health sciences have lead to increased survival of infants born prior to 33 gestational weeks, there is a greater interest in understanding the later health and development of these children as they develop. This year, multiple studies reported findings of increased risk of autism in cohorts of infants born prior to 33 weeks or with very low birth weight (less than 3 lbs, 5 ounces). Researchers studied cohorts from across the globe and screened for multiple behavioral outcomes from age 4-14 years of age, including ADHD, autism, conduct disorders, phobias, cognitive delays and emotional problems. These findings expand and complement previous reports using cross sectional designs that have identified low birth weight and gestational age as risk factors for autism1.
One set of studies followed a cohort in the United Kingdom. Investigators recruited all babies born prior to 26 weeks who were admitted to the neonatal intensive care unit. During follow-up at 2.5, 6 and 11 years, they were compared to classmates born at term. About 23 percent of children born preterm had one of the conditions studied; one of the most common conditions was ASD, which was found in 8% of the children born prematurely by age 112. In a follow up report based on questionnaire data,3it was found that extremely preterm children are especially at risk for ASD behaviors and cognitive delay.
In another study4, very low birth weight children were compared to those who were small for gestational age. At 14 years of age, the children were reexamined and assessed for autism behaviors, attention and emotional problems. Children with low birth weight were more likely to have behavioral difficulties, including problems with attention and social behavior. Another group examined the behavioral development of children who spent time in the neonatal intensive care unit5 after birth. While the prevalence of ASD in NICU graduates was no different than that in the general population, the researchers found that NICU graduates who were diagnosed with ASD were more likely to be preterm or have low birth weight. Children who were later diagnosed with ASD show differences in attention as early as four months of age, suggesting an early marker of later development.
What mechanism can explain why and how prematurity or low birth weight is a risk factor for ASD? Given the wide range of symptoms later found in children who are born extremely premature, influences of prematurity on brain development appear to be variable. The neurobiological impact of preterm birth may be part of a larger profile of cognitive, attention and functional impairments. On the other hand, premature birth may also be associated with greater sensitivity to a number of environmental factors.
2. Johnson S, Hollis C, Kochhar P, Hennessy E, Wolke D and Marlow N (2010) Psychiatric disorders in extremely preterm children: longitudinal finding at age 11 years in the EPICure Study. Journal of the American Academy of Child and Adolecent Psychiatry, 49: 453-463.
3. Johnson S, Hollis C, Kochhar P, Hennessy E, Wolke D and Marlow N (2010) Autism spectrum disorders in extremely preterm children. Journal of Pediatrics, 156: 525-531,
4. Indredavid MS, Torstein V, Evensen KAI, Skranes J,Taradsen G and Brubakk A-M (2010) Perinatal risk and psychiatric outcome in adolescents born preterm with very low birth weight or term small for gestational age. Journal of Developmental and Behavioral Pediatrics, 31: 286-294.
5. Karmel BZ, Gardner JM, Meade LS, Cohen IL, London E, Flory MJ, Lennon EM, Miroshnicknko I, Rabinowitz S, Parab S, Barone A and Harin A (2010) Early medical and Behavioral Characteristics of NICU infants later classified with ASD. Pediatrics, 126: 457-467.