How has survival improved for children with Down syndrome?

One measure of the remarkable improvements in the quality of life experienced by people with Down syndrome is childhood survival rates:

  • In the 1920s, only 20% of children with Down syndrome survived to 10 years of age
  • By 2010, over 90% of children with Down syndrome (in more developed countries) were living beyond the age of 10 years

survival-rates-children-down-syndrome-1917-2003

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Source: de Graaf G., Buckley F., Skotko B. G. (2016). Estimation of the number of people with Down syndrome in the United States. Genetics in Medicine, advance online publication. https://doi.org/10.1038/gim.2016.127

How many babies would be born with Down syndrome each year in the UK in the absence of prenatal screening?

Given we can quite accurately estimate the number of babies expected to be born given the ages of their mothers[1,2], and as we have a good idea how many babies are actually being born, it is fairly straightforward to calculate how many births are being prevented as a result of prenatal screening.

Here are estimates for the UK, based on live births data from the Office for National Statistics for England and Wales, and from National Records of Scotland and the Northern Ireland Statistics and Research Agency:

figure-births-babies-down-syndrome-uk-prenatal-screening-terminations-1991-2015

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This shows the number of live births of children with Down syndrome in each year (green bars) and the 5-year moving average live births of children with Down syndrome (red line). It also shows the additional number of live births we would expect each year had there been no prenatal diagnoses and subsequent terminations (blue bars) and the 5-year moving average for total UK births in the absence of screening (orange line). The reduction rate (the proportion of babies not born as a % of all babies expected to be born), averaged over 5 years, is also provided (yellow dashed line).

Year Live births of babies with Down syndrome 5-year UK average births Additional births in the absence of selective terminations Total births in the absence of selective terminations 5-year UK average births in the absence of selective terminations 5-yr UK average reduction rate (%)
1991 841 326 1167
1992 753 430 1183
1993 704 485 1189
1994 727 485 1211
1995 675 740 546 1222 1194 38%
1996 691 710 569 1260 1213 41%
1997 779 715 518 1297 1236 42%
1998 716 718 605 1321 1262 43%
1999 688 710 641 1329 1286 45%
2000 678 710 663 1341 1310 46%
2001 654 703 710 1365 1331 47%
2002 645 676 757 1402 1352 50%
2003 687 671 804 1492 1386 52%
2004 755 684 813 1567 1433 52%
2005 835 715 773 1608 1487 52%
2006 842 753 843 1685 1551 51%
2007 817 787 943 1760 1622 51%
2008 841 818 965 1806 1685 51%
2009 895 846 907 1803 1732 51%
2010 815 842 1030 1844 1780 53%
2011 844 842 1034 1879 1818 54%
2012 867 853 1027 1894 1845 54%
2013 814 847 1023 1837 1851 54%
2014 848 838 1006 1854 1862 55%
2015 861 847 1022 1884 1870 55%

Some observations:

  • Between 1991 and 2015, an estimated 18,925 fewer babies with Down syndrome were born in the United Kingdom as a result of prenatal screening and diagnosis and subsequent decisions to terminate pregnancies
  • In the absence of prenatal screening, we would currently expect an average 1,870 babies to be born each year with Down syndrome in the UK (compared to the 847 actually born)
  • The average reduction rate has risen from 38% in the early 1990s to 55% today (the rate at which the expected live birth rate is reduced as a result of screening and pregnancy decisions)

A common question:

  • Given registry data suggests that around 23,600 pregnancies diagnosed with Down syndrome were terminated between 1991 and 2015, how could only 18,925 fewer babies have been born? This is because a relatively high number of pregnancies with Down syndrome result in miscarriage or stillbirths. In other words, many of the terminated pregnancies would not have resulted in a live birth if not terminated.

Once again, I must acknowledge helpful discussions about the data with my colleague Gert de Graaf. However, any errors are all mine!

References

  1. Morris JK, Mutton DE, Alberman E. (2002) Revised estimates of the maternal age specific live birth prevalence of Down’s syndrome. Journal of Medical Screening, 9, 2-6. http://msc.sagepub.com/content/9/1/2.full.pdf
  2. Wu J, Morris JK. (2013) Trends in maternal age distribution and the live birth prevalence of Down’s syndrome in England and Wales: 1938–2010. European Journal of Human Genetics, 21, 1016–1019. https://doi.org/10.1038/ejhg.2012.294

How many babies with Down syndrome are currently born each year in the United Kingdom?

I am not sure why, but the figure most often quoted for the number of babies with Down syndrome born each year recently in the UK is 750. I am guessing this figure is drawn on data published the National Down Syndrome Cytogentic Register.  However, this is does not cover the whole of the UK – only England and Wales.

England and Wales is fortunate to have a registry recording the births of babies with Down syndrome. It has reported live births, prenatal diagnoses and pregnancy outcomes since 1989 with a high degree of accuracy. In fact, it offers probably one of the most useful datasets available anywhere in the world.

Rather irritatingly, the work of NDSCR has recently been transferred the National Congenital Anomaly and Rare Disease Registration Service (NCARDRS) and the Congenital Anomaly Register and Information Service (CARIS) for Wales. The move around means no data for 2014 or 2015 has been published for England. I am told it will be next year before this appears. CARIS only appears to be reporting total cases, which is unhelpful. Hopefully, the NCARDRS and CARIS will pool their data to continue to publish the England and Wales data series.

Scotland reports live births back to 1991, though apparently not prenatal diagnoses and pregnancy outcomes. Northern Ireland does not seem to publish data on live births of babies with Down syndrome.

Drawing on these data sources, we can compile a total for UK live births going back to 1991:

figure-births-babies-down-syndrome-uk-england-wales-scotland-northern-ireland-1991-2015

As Northern Ireland does not seem to publish a count of live births of babies with Down syndrome, I have estimated them by taking published data on all live births broken down by age of mother and multiplying these by the formula expressing the maternal-age-related chance of having a baby with Down syndrome (to get the expected number of ‘natural’ live births in the absence of selective terminations). I have then reduced this number at the same rate as ‘natural’ live births have been reduced by terminations in each year in England and Wales. To estimate births in 2014 and 2015 for England and Wales, and for 2012-15 for Scotland I have again calculated the expected ‘natural’ live births and reduced by the recent average reduction rates in each area. (Of course, the reduction rates may have risen in the past few years with the private availability of NIPT, but we do not have the data yet to see this.)

Given these assumptions, we can calculate that the average annual live births of babies with Down syndrome in the United Kingdom over the past 5 years is 847.

Year England and Wales Scotland Northern Ireland UK 5-year UK average
1991 737 75 29 841
1992 663 65 25 753
1993 621 60 23 704
1994 639 64 24 727
1995 581 73 21 675 740
1996 607 62 22 691 710
1997 667 88 24 779 715
1998 633 60 23 716 718
1999 604 63 21 688 710
2000 594 64 20 678 710
2001 580 54 20 654 703
2002 589 36 20 645 676
2003 616 51 20 687 671
2004 665 68 22 755 684
2005 747 64 24 835 715
2006 764 53 25 842 753
2007 723 70 24 817 787
2008 754 61 26 841 818
2009 793 76 26 895 846
2010 737 53 25 815 842
2011 758 61 25 844 842
2012 779 63 26 867 853
2013 728 62 24 814 847
2014 759 64 25 848 838
2015 774 62 26 861 847

As ever, I must acknowledge helpful discussions about the data with my colleague Gert de Graaf. As soon as we can get the most recent data I hope we will publish a larger historical births and populations dataset. However, any errors are all mine!

Births and populations of people with Down syndrome

Over the past few years, I have been privileged to work with colleagues Gert de Graaf and Brian Skotko looking at the data on births and trends in populations of people with Down syndrome.

We have now published three papers together. The first looked at the births of babies with Down syndrome in the USA from 1900 to 2010. The second reported a similar analysis for the state of Massachusetts. The third, recently published online ahead of publication in Genetics in Medicine, estimated the population of people living with Down syndrome in the USA from 1950 to 2010. This work builds on the previous work of Gert and colleagues developing a model for estimating the population prevalence of Down syndrome.

We have produced a freely downloadable factsheet with some of the key figures from our papers.

Our findings include:

  • The live birth prevalence of Down syndrome in the US in most recent years (2006–2010) was 12.6 per 10,000, with around 5,300 births annually
  • During this period, an estimated 3,100 Down syndrome related elective pregnancy terminations were performed in the US each year
  • As of 2007, the estimated rate at which live births with Down syndrome were reduced in the US as a consequence of Down syndrome related elective pregnancy terminations was 30%
  • The number of people with Down syndrome living in the US grew from 49,923 in 1950 to 206,366 in 2010
  • The population of people with Down syndrome living in the US includes 138,019 non-Hispanic whites, 27,141 non-Hispanic blacks, 32,933 Hispanics, 6,747 Asians/Pacific Islanders, and 1,527 American Indians/American Natives
  • The population prevalence of Down syndrome in the US, as of 2010, was 6.7 per 10,000 inhabitants (or 1 in 1,499)
figure-births-down-syndrome-usa-1900-2010
Live births of babies with Down syndrome in the USA, 1900-2010
figure-population-down-syndrome-usa-1950-2010-ages
The population of people living with Down syndrome in the USA, 1950-2010
figure-population-down-syndrome-usa-2010-immigration-terminations
The population of people living with Down syndrome in the USA, 2010, and the effects of immigration and selective terminations of pregnancies

We are hopeful this work will provide a baseline from which we can track the impact of new screening technologies and changing social attitudes on future populations of people with Down syndrome.