Why has the prevalence of Down’s syndrome births increased in the US, but not the UK?
It is not much of a surprise to see that the number of children born with Down’s syndrome has increased in the US, according to a recent study. What is surprising is the rate of increase. According to new data from the Centers for Disease Control and Prevention published in Pediatrics, “From 1979 through 2003, the prevalence of DS at birth increased by 31.1%, from 9.0 to 11.8 per 10000 live births in 10 US regions.”
That is an enormous increase. Consider that, according to UK statistics, the number of children born with Down’s syndrome in the England and Wales decreased 1% between 1989/90 and 2007/2008, while the number of diagnoses increased 72%.
Comparing with data on total births from the Office of National Statistics we find that the prevalence in the UK in both 1990 and 2007 was 10.7 per 10000 live births.
One of the reasons given for the increase in US rates is higher maternal age, which is certainly the major factor in the increase in diagnoses. But why is it that the prevalence of Down’s syndrome live births has increased to such a degree in the US, while remaining flat in the UK?
An obviously explanation would be a lower rate of abortions in the US, but reports in the US and UK (and elsewhere) are pretty consistent in showing a 90+% termination rate. The only other thing that springs to mind is that the US figures span 1979-2003 while UK figures span 1990-2007.
Doubtless there was an increase in the quality of care and medication between 1979 and 2003 that would have contributed to greater numbers of children with Down’s syndrome making it to term. Likewise between 1990 and 2007. Could the rate of improvement in quality between 1979 and 1990 have been higher than between 1990 and 2007? Quite possibly. I’m not sure that would be enough to explain the variation between US and UK figures, however.
UPDATE – WTI was honoured with a visit from Frank Buckley, CEO of Down Syndrome Education International (if I’d known he was coming I’d have tidied up a bit) who points out that since the early 1990s the trends are strikingly similar.
These trends appear to support the suggestion that there were dramatic improvements in the US between 1979 and the early 1990s – but also suggest that there was a considerable decline in the UK between 1990 and 1995. They also indicate that the result you get depends on where you start measuring. – UPDATE