Autism spectrum disorder and birth spacing: Findings from the study to explore early development (SEED).
Laura A Schieve, Lin H Tian, Carolyn Drews-Botsch and 6 others
PMID 29164825WHAT IT FOUND
In second or later births, autism was associated with conception less than 18 months or 60 months or more after a previous birth.
The association was stronger for more severe autism; other developmental delays showed no association.
Key findings
01In children born in second or later births, autism was associated with conception less than 18 months or 60 months or more after the mother's preceding birth.
02Non-ASD developmental delay was not significantly associated with either short or long birth spacing.
03Associations were stronger for more severe ASD and were attenuated and no longer statistically significant for less severe ASD.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
This is an observational case-control study, so it cannot prove that birth spacing caused autism. The analysis included only second or later births, so it says nothing about first births. The study could not fully assess preterm births because sample sizes were small, and the association was not seen among preterm births. Some families initially targeted for recruitment could not be located, so selection bias cannot be ruled out. The general population control group was not fully screened for disabilities except autism, which could slightly weaken some associations. The study adjusted for several factors, but it lacked data on possible mechanisms such as folic acid and inflammation.
Declared interests
No competing interests were declared. Funding is not reported in the article text.
The easy way to misread this
Do not read the association as proof that birth spacing causes autism. The study compared children with autism, other developmental delays and population controls, so it cannot show that changing the interval between pregnancies would have changed the child's autism risk.