I am newly pregnant (seven weeks), I am 35, and my partner is 51. I read Expecting Better and can see all the risks of my being 35 relating to chromosomal defects. But what about my partner being 51 — is there good data on the risk of his sperm “causing” defects because of his age? Or is it too hard to look at both factors (mom and dad) at the same time in studies?
—Emily
Obviously, as you note, the most challenging problem with your question is the difficulty of separating maternal and paternal age. We know that maternal age is a risk for birth defects, and people tend to have children with partners of similar ages.
Of course, the ages aren’t usually identical, so it is possible to do this analysis.
The most consistent set of findings about paternal age are about autism or other neurological disorders. Children born to older fathers are more likely to have diagnosed autism. One meta-analysis puts the risk at 2.5 times as high for fathers over 50 relative to those 20 to 29. A more recent review showed similar impacts.
These analyses do try to adjust for maternal age, but it’s challenging to do that well. A closely related concern is that men who have children at older ages differ in other ways — ways that might change the incidence of autism (and its diagnosis rate). I thought this paper summarized the overall picture well: it’s clear that the rate of these issues goes up with paternal age, but we do not have any real sense of mechanisms, and it’s very difficult to know how much is selection and how much is (say) more mutations in older sperm.
I wrote much more about this in FiveThirtyEight years ago, so if you want to read a lengthy discussion, I’d direct you to that article. I also talk there about impacts on fertility (limited) and engage in a long-form rant about a particular paper that tries to address the link with neurological disorders using a sibling fixed-effects analysis.
I wish I had a better answer! These questions are hard.
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