Something missing from this analysis is that the expected probability of these conditions for any given pregnancy is not the same as the incidence in the population at large. The factor that I’ve most often heard about is increasing age being highly associated with increasing incidence of Down syndrome, though there may be others, and I’m not sure whether there are known correlates with the other conditions you mention.
That might also relate to the last point about incidence of these conditions in the wider population and the incidences that study reported. It could be that older pregnant people are more likely to opt for the test, knowing that they are at elevated probability.
You finish by suggesting people think about prevalence differences shifting by a factor of two, but from a quick Google, it looks like age can shift prevalences by orders of magnitude. The first table that popped up suggested 1 in 2000 at age 20, increasing to 1 in 100 at age 40 and 1in 10 at age 49.
(Also not medically trained.)
Something missing from this analysis is that the expected probability of these conditions for any given pregnancy is not the same as the incidence in the population at large. The factor that I’ve most often heard about is increasing age being highly associated with increasing incidence of Down syndrome, though there may be others, and I’m not sure whether there are known correlates with the other conditions you mention.
That might also relate to the last point about incidence of these conditions in the wider population and the incidences that study reported. It could be that older pregnant people are more likely to opt for the test, knowing that they are at elevated probability.
You finish by suggesting people think about prevalence differences shifting by a factor of two, but from a quick Google, it looks like age can shift prevalences by orders of magnitude. The first table that popped up suggested 1 in 2000 at age 20, increasing to 1 in 100 at age 40 and 1in 10 at age 49.