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