Autism risk increases with low birth weight

October 20, 2011

Knowledge of a child’s birth weight can be a valuable tool when determining whether to screen for autism spectrum disorder. Patients who weigh less than 2,000 g at birth are 5 times more likely to have autism than the general population. How much does the autism incidence increase with a history of very low birth weight (less than 1,500 g)?

Recent research has found a strong relationship between autism spectrum disorder (ASD) and low birth weight, with the lower the weight at birth, the higher the risk of autism.

Researchers found that patients who weigh less than 2,000 g at birth are 5 times more likely to have autism than the general population. The regional study of 1,105 low-birth-weight infants found a 5% prevalence of ASD. The Centers for Disease Control and Prevention (CDC) report that just under 1% of US 8-year-olds have ASD.

The study followed children born in 3 New Jersey hospitals from 1984 to 1987 who weighed between 500 g and 2,000 g at birth. The World Health Organization defines low birth weight as less than 2,500 g-up to and including 2,499 g-regardless of gestational age.

At 16 years, nearly 19% of the 623 adolescents still in the study had a positive screen for ASD using the Social Communication Questionnaire or the Autism Spectrum Symptoms questionnaire or previous professional diagnosis reported by a parent. Cutoff points on both assessments were set substantially lower than customary for a positive screen.

At 21 years, 60% of participants who had screened positive and 24% of those screened negative were tested using the Autism Diagnostic Observation Schedule or the Autism Diagnostic Interview-Revised.

Of the screen-positive group, 14.3% had ASD, as did 2.5% of the screen-negative group. Researchers calculated that 5% of the total adolescent cohort had ASD.

Researchers found that the lower the weight at birth, the higher the risk of ASD. Among those born weighing less than 1,500 g, the prevalence was 10.6% compared with 3.7% among those weighing between 1,500 g and 2,000 g. Boys were 3 times more likely to have ASD (9.9%) than girls (3.3%). About 3% of US births fall in the 500 g to 2,000 g weight range studied.

A high number of participants were lost to follow-up during the course of the study. Of the initial 1,105 children, 623 remained in the study at 16 years and 189 at 21 years.

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