Shorter Gap Between Pregnancies Linked to Increased Autism Risk

[Guest guest]

By KATIE MOISSE

ABC News Medical Unit

Shorter Gap Between Pregnancies Linked to Increased Autism Risk

Study Supports Role for Environmental Risk Factors During Pregnancy Jan. 10,

2011

The rising prevalence of autism in the United States

suggests that environmental risk factors growing in p

rominence are at play. New research adds to a

growing body of evidence that the risk is conferred

well before affected children show symptoms, such as

impairments in communication and social interaction

during pregnancy.

According to the study published in Pediatrics,

children conceived within one year of a sibling were

three times more likely to be diagnosed with autism

than those conceived after three years or more. The

association held true even when the study authors

controlled for variables such as parental age, preterm

birth and low birth weight – all factors known to

increase autism risk.

" We've identified a really robust association, " said

Bearman, director of the Lazarsfeld Center for

the Social Sciences at Columbia University and senior

author of the study. " When you see something so

robust and so stable, it provides an important clue as

to what we should be looking at next. "

The risk of autism among children conceived 1-2

years after an older sibling was almost double, the

researchers reported.

The study focused on over 660,000 second-born

sibling children born in California between 1992 and

2002. During that period, the proportion of births

occurring within 24 months of a previous birth

increased from 11 percent to 18 percent, according

to the researchers.

" Closely spaced births occur in some part because of

unintended pregnancies but also by choice,

particularly among women who delay childbearing, "

they wrote.

The mechanism by which closely spaced pregnancies

may boost autism risk remains unclear, but the

authors offered two possible explanations: Autistic

behaviors might be more noticeable when there's an

older sibling close in age for comparison; or a

biological factor, such as maternal depletion of

nutrients like folate, -- important for brain

development -- could put the developing fetus at

risk.

" I think it's likely both, " said Bearman. " The next step

will be to decompose this and figure out which piece

of puzzle is explained by what. "

Autism on the Rise

Over the last 40 years, the prevalence of autism

spectrum disorders – a group of conditions that

includes autism, Asperger syndrome and pervasive

developmental disorder – has risen 10-fold to

roughly one in 110 children, according to CDC data

from 2006.

Work done by Bearman and colleagues has shown

that awareness increases the odds of a child receiving

a diagnosis of an autism spectrum disorder. But

awareness unlikely to account for the dramatic,

ongoing rise in prevalence, according to Dr.

Insel, Director of the National Institute of Mental

Health.

" You might have called these kids something different

before, but you would have called them something, "

said Insel. " I think awareness contributes on the

modest end. "

As for Bearman and colleagues' theories about the

association between closely spaced pregnancies and

autism risk, Insel is skeptical.

" Most parents don't forget when their children started

talking, " he said, explaining that an extra year or two

between children is unlikely to make missed

milestones go unnoticed. " I don't think that's it. "

But the folate depletion hypothesis doesn't stack up

either, Insel said.

" The reality is, there were real issues with folate and

iron deficiency 40 years ago, and that's not when we

had autism, " Insel said. " This paper adds one more

edge piece to the very large jigsaw puzzle. "

Autism is a complex set of disorders with overlapping

genetic and environmental -- both social and

biological -- contributors, making it difficult for

researchers to understand its underlying causes and

develop appropriate treatments.

" I think we've made tremendous progress over the last

couple years in areas of genetics and what's

happening in the brains of children with autism, "

Insel said. " Now we need to focus on environmental

factors. "

Pregancy: Risky Period?

This study supports the idea that whatever

environmental factors are leading to the increase in

autism, they're probably active during pregnancy,

Insel said. Research linking autism and early

childhood vaccination published by

Wakefield and colleagues a decade ago was deemed

fraudulent in a Jan. 5 editorial published in the British

Medical Journal.

But until researchers uncover specific risk factors,

parents who are expecting or planning to get

pregnant shouldn't worry about autism risk, Insel

said.

" This is still an odd and rare occurrence, " Insel said.

Although 1,188 children conceived within 12 months

after a sibling were diagnosed with autism, 154,846

children were not.

" Even with a closely spaced pregnancy, 99 times out

of 100 you're not going to have a child with autism, "

Insel said.

" I think it's likely both, " said Bearman. " The next step

will be to decompose this and figure out which piece

of puzzle is explained by what. "

Over the last 40 years, the prevalence of autism

spectrum disorders – a group of conditions that

includes autism, Asperger syndrome and pervasive

developmental disorder – has risen 10-fold to

roughly one in 110 children, according to CDC data

from 2006.