A study published yesterday in the journal Pediatrics reports a surprising finding about autism risk within families: when a second child is born too close to the older sibling, the incidence of autism goes up.
It’s a result that surprised researchers, but the population of California children studied was very large — more than a half-million — and the effect remained even after other risk factors like age of the parents were taken into consideration.
The study found that children born less than two years after their older sibling were considerably more likely to be diagnosed with autism than those who were born at least three years after their older sibling.
Here’s why the researchers say closely-spaced kids could be at higher risk for autism:
One possibility is that pregnancy depletes the body of certain nutrients, like folate, and that could put moms at risk for not having sufficient stores the second time around. Studies have already shown that closely-spaced births are more likely to result in low birth weight or premature babies, which could be tied to folate as well.
The other possibility is that with babies close in age, the parents are more likely to see the differences in development and catch on to bumps in the road early. If there is only 18 months between kids, things like speech delays could be more obvious.
But autism is a complicated puzzle, and this is just a signpost for researchers to put up and continue their work. We don’t know why this result came up, and it hasn’t been replicated — nonetheless, it’s an interesting piece to add to the picture.
But the researchers also said that closely-spaced siblings (under two years apart) are becoming more common in this country — in 1995 it was 11 percent, and in 2002 it was 18 percent. That could be because more couples are waiting to have children, and if they want more than one, they might have them closer together because of age.