Risk factors for autism remain elusive: study
A problem in the studies that have focused on factors around the time of birth is that they have generally included relatively small groups of children, Gardener said. So for their study, her team combined the results of 40 studies -- in what's called a meta-analysis.
They found that a number of "perinatal" (around the time of birth) and newborn factors were linked to autism -- that is, infants affected by those factors were relatively more likely to go on to develop autism than unaffected infants.
Along with low birth weight, fetal distress, and umbilical cord-problems (the cord being wrapped around the baby's neck, for instance), other factors included multiple birth, birth injuries to the baby, maternal hemorrhaging during childbirth, anemia or jaundice in the newborn. Another was low Apgar score -- a measure of a newborn's general health that includes heart rate, breathing and muscle tone.
But, the researchers write, there was "insufficient evidence to implicate any one perinatal or neonatal factor in autism etiology."
There was, though, some evidence that exposure to a "broad class" of those factors may contribute to autism risk -- possibly reflecting "general compromises" to a newborn's health.
But even where associations exist, it's not clear why they do.
Take low birth weight as an example. Gardener said it is unlikely that low birth weight, per se, is a risk factor for autism. Instead, low birth weight is a "marker" of problems in fetal development -- it could indicate anything from genetic influences to dysfunction in the womb to poor nutrition.
It's not clear which, if any, of those things might in turn fuel autism development. A big obstacle, Gardener pointed out, is that researchers still do not know what biological mechanisms ultimately lead to autism.
That said, the current study did find that a number of birth factors showed no relationship to autism.
Those included use of anesthesia, forceps or vacuum during childbirth, high birth weight and newborn head circumference.
SOURCE: http://bit.ly/pL6Rey Pediatrics, online July 11, 2011.
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