I read an article by the GREAT Dr Sarah Buckley, who had some other information backing her up that these stats are skewed because of the demographic of people seeking fertility treatment.
Now, it was a while ago that I read this, but I think the gist of it was that we have thought of older women as having more chance of a having a baby with 'defects' because when there are not so many in that age range having babies as younger women the 'defects' cases seem disproportionate, AND these are the women presenting to fertility specialists for tests of their eggs. As opposed to all the other women in that age bracket who AREN'T presenting to fertility specialists asking for their eggs to be tested.
There is some current thinking (outside of the vested interest group of fertility specialists!) that the incidence is no higher in that age range than in any other age range, but with more women in younger age ranges giving birth the incidences are more spread out. As well as these younger women, for the most part, aren't asking for their eggs to be tested because they don't believe they are in a risk category. So, you get younger women who have babies with 'defects' but because they aren't in the traditionally 'risky' age range, other things get looked at instead, like genetics.
So, Buckley is saying it's a bit of a myth that it's older women - it's not like they were testing at age 23 and then at age 41 and noticing a massive jump. Clearly, if you're 41 and at a fertility specialist in the hopes of having a baby, you haven't been having babies since early 20s (and being tested) to notice you're 'output' is 'defective', and if you have, then you'd know it wasn't because of your age
So age is not the thing to be worried about if you're older and considering having a baby or about to have one - if you're eggs are showing up with 'defects', there's something else going on and you're better off chasing more productive lines of inquiry than being fobbed off with the 'age' thing. It's a matter of statistical incidence, and there is no sound population data to base it on.
I mean, how many 'bonus' babies do you see get born in older women who don't have these 'defects' (sorry, I do use the inverted commas because some 'defects' are problematic for me when termed that way), and if properly researched and compared with the younger population, I reckon it would wash up about even. So does Dr Sarah Buckley.
Does that make sense? I'm happy to be challenged, because I'm not going to defend it, I'm just reiterating a line of argument that really resonated with me and gave me a 'light bulb' moment (having had family friends have healthy and some not so healthy babies in older age groups). Read up on Sarah Buckley if you want to know more for some reassurance.