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Autism risk increases with back to back pregnancies

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by  Aimee Keenan-Greene 

A new study in the journal Pediatrics suggests children born close in age could be at a greater risk for developing autism.  

Autism is a neurological disorder that affects the functioning of the brain, specifically social interaction and communication skills. Children and adults with autism typically have difficulties in verbal and non-verbal communication, social interactions, and leisure or play activities. 

Autism is the most common of the Pervasive Developmental Disorders, affecting an estimated 2 to 6 per 1,000 individuals, according to a document released in 2001 by the U.S. Centers for Disease Control and Prevention. This means as many as 1.5 million Americans today are believed to suffer some form of autism, according to the Autism Project of Rhode Island.

The U.S. Department of Education estimates autism is growing at a rate of 10-17 percent per year.

The number of children with autism in Rhode Island's public schools increased more than 1,500 from 1992 to 2002.

Keely Cheslack-Postava, PhD, coauthor of the study and colleagues from the Robert Wood Johnson Foundation Health and Society Scholars, Columbia University, and Paul F. Lazarsfeld Center for the Social Sciences, Columbia University, concluded shorter interpregnancy intervals (IPI), especially with pregnancies spaced less than a year apart, put an infant at an increased risk of developing autism.

The researchers looked at pairs of first and second-born singleton full siblings identified from all California birth records spanning 1992 to 2002. Diagnoses were identified by using linked records of the California Department of Developmental Services. IPI was calculated as the time interval between birth dates minus the gestational age of the second sibling. 

The study found an inverse association between IPI and odds of autism among 662,730 second-born children.  Specifically, IPIs of under 12 months,  12 to 23 months, and 24 to 35 months were associated with odds ratios, 95 percent confidence intervals, for autism - 3.39 (3.00–3.82), 1.86 (1.65–2.10), and 1.26 (1.10–1.45) relative to IPIs of more than 36 months. 

The association was not affected by preterm birth or low birth weight and persisted across sociodemographics, with some attenuation in the oldest and youngest parents.

Scientists say logistic regression models were used to determine whether odds of autism in second-born children varied according to IPI. 

According to the Autism Project of Rhode Island, autism is four times more prevalent in boys than girls. 

For more information on Autism in Rhode Island, click here.

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