Older Parents, 1st Born Child: Autism More Likely?
October 25, 2008 by Kristina Chew, PhD
Filed under Health
1st born child—-older mother—-older father: Such a child is three times more likely to develop autism than third- or later-born offspring of mothers who are 20–34 years and fathers who are less than 40 years old, according to a study published in the October 21st American Journal of Epidemilogy (full text can be accessed here and this is a PDF file; another summary at the Daily Telegraph). Researchers reached these conclusions after studying records for more than 253,347 children born in 1994 of whom 1,251 have autism.
Researchers note that there has been a decline in average family size in recent decades:
The results of this study raise the question of whether some portion of the recent rise in ASD prevalence may be linked to recent trends in parental age and family size. A further question is whether a modest increase in prevalence associated with advancing parental age and low birth order may have contributed to a greater awareness of ASD and, in turn, increases in measured prevalence. The tendency for older parents of firstborn children to have higher levels of educational achievement and resources than other parents could further contribute to increased awareness and an expansion of the diagnosis of ASD.
While it’s not clear how advanced parental age might contribute to increased risk for autism, the researchers note that the “probability or selection of [gene] mutations increases as men age”; in older mothers, “age-related chromosome changes, pregnancy complications, or environmental exposures during pregnancy” are possibilities. Also noted is the potential role of infertility treatments or assisted reproductive technologies,” the use of which has increased recently and among “women and men of advanced reproductive age,” and, too, the “psychopathology or behavioral traits of parents that may result in both delayed parenthood and genetic susceptibility to autism in offspring.” Two other studies that have found increased risk of autism in first-born children are cited.
Charlie is our first-born (and our only child). I was between 20–34 years old when he was born and Jim was less than 40 years old.
These studies all end up looking like waffle to me. We’re trying to find these causes to a bunch of symptoms that add up to autism, probably caused by at least half a dozen different things.
Our sample of one; Hubby and I were both under 25 when we had our children and only our second child is Autistic (not our first).
I also wonder whether or not the age of the baby is a factor.
Most babies? Born at the age of zero. But I have such a terrible sense of direction that I didn’t pop out till the age of 14.
(which was a huge relief for my mother. despite the difficult birth, she was finally able to understand why one diet after another had failed).
Anyway. I just wonder if that’s related to my diagnosis. Hmm. Pondering ensues.
Had TH when we were both 32. Had Dubya when we were 34. Had our youngest when we were 38. Really, our least “spectrumy” child is the middle one.
@M: ROFL!
@M, as I read your comment, I kept envisioning the birth of Athena (full grown, fully armored) from Zeus’ head……..
20 to 34 is a huge age gap. Since when is 21 too old to have a first kid.
I don’t think this study means anything.
They just pick ages most people have children.
Maybe they got it wrong and the first born is more likely to be autistic of most age groups.
There may be different factors at work for women vs. men in the association between advanced parental age and autism in their children. In the case of women, those over 35 years old usually undergo additional ultrasound scans. Mouse experiments have shown that prenatal ultrasound disrupts neuronal migration, which “wires” the brain. Older first-time mothers would be more likely to undergo prenatal ultrasound scans for many reasons, such as to view follicle development during fertility treatments, to confirm pregnancy at only five or six weeks of gestation, or for genetic testing such as chorionic villus sampling or amniocentesis, all of which may subject the developing embryo to increased risk. Older mothers are also more likely to have assisted reproduction, which is guided by ultrasound. If ultrasound is a factor in causing autism, it would explain why the population of older first-time mothers is more likely to have children with autism than younger mothers.
In the case of men, something as apparently frivolous as the style of underwear favored by a particular age group could be a factor, as it is known that jockey briefs, for instance, damage sperm production by causing the testes to be held so close to the body that they become overheated. Studies that indicate an association do not necessarily prove causation. However, the discovery of an association does indicate where researchers should focus additional attention.