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.

Why do counts of terminations of pregnancies diagnosed with Down syndrome in England and Wales differ?

Following yesterday’s Mail on Sunday article and my observation that the data quoted was wrong, many people have asked how the Department of Health abortion statistics can be so different from the terminations recorded by the National Down Syndrome Cytogenetic Register.

The Mail on Sunday reported 693 abortions “linked to Down syndrome” in 2014. This figure comes from figures for England and Wales compiled by the Department for Health (DH). These differ from those reported by the National Down Syndrome Cytogenetic Register (NDSCR).

The DH data comes from forms completed by registered practitioners terminating pregnancies. NDSCR collects data from the cytogenetic laboratories that analyse samples obtained through amniocentesis or chorionic villus sampling (CVS) to diagnose (or not) Down syndrome in pregnancies.

The DH data consistently underreports Down syndrome diagnoses:

2011 2012 2013 2014
National Down Syndrome Cytogenetic Register
Terminations of pregnancies diagnosed with Down syndrome 1134 1131 1108
Department of Health
Abortions by principal medical condition 512 544 590 662
Mentions by principal medical condition 570 613 693
Difference
Number not counted in DH data 622 587 518
Number not counted in DH data as % NDSCR count 45% 48% 53%

These differences were investigated in data matching exercise undertaken by the DH and a review undertaken by the Royal College of Obstetricians and Gynaecologists – published last year.

The NDSCR has recently been merged into a new National Congenital Anomaly and Rare Disease Registration Service (NCARDRS). NDSCR data for 2014 is yet to be published. However, my understanding is that not substantial changes have been detected in the data collected by NDSCR for 2014 and that increases in the abortions recorded as due to a diagnosis of Down syndrome in the DH data are a result of efforts to improve reporting by practitioners terminating pregnancies.

 

 

 

 

Selective terminations of babies with Down syndrome have not risen by 35% in three years

piece in the UK Mail on Sunday claims Department of Health statistics show “women choosing to abort babies with Down’s syndrome and other serious disabilities soars 34% in three years” and that “the biggest proportion was linked to Down’s syndrome, with 693 terminations last year compared with 512 in 2011”. Data collected by the National Down Syndrome Cytogenetic Register (NDSCR) shows this is not the case.

UPDATE (15 June): Amended to correct dates. Mail article refers to 2014 Department of Health data, while NDSCR has only reported to 2013. It remains the case that (a) NDSCR data reports 2% drop between 2011 and 2013 – which is not consistent with 35% rise over 3 years, and (b) DoH abortion statistics since 2011 consistently differ from NDSCR data. More here.

There is a remarkable headline in The Mail on Sunday today claiming terminations of babies with Down syndrome have “soared 34% in three years”. It quotes “an investigation into figures published by the Department of Health”.

In England and Wales, there is a national registry collecting data on prenatal and postnatal diagnoses. Their data (collected since 1989) is widely cited in academic studies and is 94% complete. I’m not sure where the Mail on Sunday (and perhaps more worryingly, the Department of Health) are sourcing their information, but it is way off.

The article claims there were 512 terminations of pregnancies diagnosed with Down syndrome in 2011 and 693 in 2014 – a rise of 181 (35%).

NDSCR reports 1,134 terminations of pregnancies diagnosed with Down syndrome in 2011 and 1,018 in 2013 – a fall of 2% over two years. NDSCR has not yet reported on 2014.

This graph shows the number of terminations of pregnancies diagnosed with Down syndrome (columns) and terminations as a percentage of all diagnosed cases (prenatal and postnatal).

down-syndrome-terminations-england-wales-2004-2013

(Note: The % terminated statistic is not the reduction rate – i.e. the rate at which live births are reduced as a result of screening and selective terminations. This is because approximately 23% of the terminated pregnancies would not have resulted in a live birth.)

Terminations of babies with Down syndrome in England

Last weekend, the UK Sunday Times reported that many terminations of babies with Down syndrome are not being correctly recorded by the Department of Health. In many reports that have since appeared online it has been stated that in England 92% of babies with Down syndrome are terminated. This is incorrect.

You would think from some of the reports and comment that have appeared online in the past week that the births of virtually all babies with Down syndrome in England are prevented through prenatal screening and selective terminations. This is not the case:

It is true that 92% of diagnosed pregnancies are terminated. However, this is very different from 92% of all pregnancies. Many people choose not to screen. Many who are screened and receive a ‘high risk’ result choose not to have invasive diagnostic testing as it carries a risk of miscarriage. Some who are screened and do not receive a ‘high risk’ result will, in fact, go on to have a baby with Down syndrome.

Overall, the rate at which live births are reduced due to prenatal diagnosis and selective terminations in England and Wales in recent years was around 50%-55%.

There are around 250,000 people with Down syndrome living in the US – not 400,000

A paper published recently in The Journal of Pediatrics estimates the population of people with Down syndrome alive in the USA in 2008 – not the oft-stated 400,000. Even this may be an overestimate.

It is important to understand the size and the demographics of populations of people with Down syndrome in order to plan services. In an important paper, recently published online by The Journal of Pediatrics, Angela Presson and colleagues present an estimate of the current population of people with Down syndrome living in the USA in 2008, which they calculate to be 250,700 with a 90% uncertainty interval of 185,900-321,700.

This is substantially lower than the 400,000 figure that is often given as the number of Americans living with Down syndrome. It is not clear what this traditional figure is based on, but it seems to confuse birth prevalence with the population (of all ages) prevalence. Because the proportion of babies born with Down syndrome varies over time and because people with Down syndrome do not live as long as other people and longevity trends have been changing over time, birth prevalence and population prevalence are quite different. For example, a study using data from 10 population registries in the US reported a live birth prevalence rate of Down syndrome of 11.8 per 10,000 live births in 2003. If applicable nationally and assumed to be the population prevalence, and given a 2003 population of 290,107,933, then we could estimate a population of 342,327. Still not 400,000, though.

Furthermore, the same 2009 paper reports the population prevalence of Down syndrome among children and adolescents aged 0 to 19 years in 2002 in 10 US regions to be 10.3 per 10,000. Using this as the prevalence rate for the population of all ages in 2003 would give a lower estimate of 298,811. Of course, the prevalence rate Down syndrome among people aged over 19 years will actually be lower, and therefore this is most likely an overestimate.

It could be argued that recent birth and youthful population prevalence rates underestimate historic prevalence rates because of the availability of prenatal diagnosis and selective terminations since the 1970s. However, at the same time many more babies have been conceived as parents choose to have children later in life. Moreover, improved healthcare as markedly improved survival rates for children with Down syndrome over the past 30 years – particularly those with cardiac defects.

There is no national birth registry in the US, and no census data and few studies of the population of people with Down syndrome. So, how did the authors of the study arrive at their estimate for the US population of people with Down syndrome? Put simply, the authors (a) estimated the number of births and (b) estimated the ages at which those born died – and therefore those who were still alive.

The study authors estimated births using (a1) data on the maternal-age-specific chances of giving birth to a baby with Down syndrome combined with (a2) data on all births of babies and the ages of their mothers and (a3) an adjustment for the impact of prenatal diagnosis and subsequent selective terminations. The authors estimated age of death by looking at the average age of death of people with Down syndrome where recorded in death certificate data from 2006 and 2007.

The maternal-age-specific chances of giving birth to a baby with Down syndrome (a1) are known with reasonable certainty and large and reliable data sets on births are maintained (a2) in the US. We can therefore quite accurately calculate the number of babies who would be expected to be born in a given year in the absence of selective terminations. For example, using these methods it is possible to calculate around 350,000 babies would probably have been born in the US in the past 60 years in the absence of selective terminations.

Unfortunately, there is limited data on the impact of prenatal diagnosis policies and technologies since the 1970s in the US. The authors of this study use an adjustment factor based on data reported putting the ratio of live births to live births + terminations at 0.874. They apply this adjustment to their estimates of births in each year from 1980 to 2007.

There are some potential problems with this estimate of the impact of selective terminations on live births. Firstly, the authors assume that the ratio of live births to live births + terminations remained constant during this period. Two factors influence this ratio: the proportion of pregnancies diagnosed prenatally and the choices of expectant parents when receiving the diagnosis. Unfortunately, the paper the authors cite in support of the constancy of this ratio only looks at termination rates – in other words the rate at which expectant parents choose to terminate given a diagnosis. This averages at around 91% (following the decision to have an invasive diagnostic test) and, as far as we can tell, has not fluctuated much over the past 20 years. However, during this time, the availability of prenatal screening tests has changed substantially, with their widespread offer to women of all ages being relatively recent. In England and Wales (where we have a national registry), for example, the ratio of live births to live births + terminations went from 0.71 in 1989 to 0.40 in 2011.

Secondly, the number of terminations is not the same thing as the number of births prevented. This is because quite a high proportion of pregnancies with Down syndrome are lost. In other words, many of the pregnancies terminated would not have resulted in a live birth. For example, in England and Wales, the recent ratio of live births to live births + terminations of 0.40 suggests a live birth reduction rate of 60%. It is, in fact, closer to 50%.

Thirdly, the rate seems very low. The authors assume live births are 12.6% lower from 1980 to 2007 than those expected in the absence of selective terminations. I previously mentioned that a study using data from 10 population registries in the US reported a live birth prevalence rate of Down syndrome of 11.8 per 10,000 live births in 2003. The authors estimate that births in that year would have been around 7,000 in the absence of selective terminations. If correct, this would have been a live birth prevalence of 17.1 per 10,000. If this were the case, the rate of reduction of births resulting from selective terminations would have been 31.0% – not 12.6%. The live births at least for part of the period from 1980 to 2007 may therefore be overestimated.

It should be noted that estimates of population prevalence derived from births and survival estimates do not account for the effects of immigration and emigration. (Migration effects may also distort population samples.) There is (and has been) net immigration in the US and it is therefore possible that such estimates fail to account for immigrants with Down syndrome. However, it seems unlikely that there are (or has been) a high number of immigrants with Down syndrome, nor that the prevalence of people with Down syndrome among immigrants in general is disproportionately high. Indeed, the opposite may be more probable

In conclusion, this study makes it clear that the suggestion that there are 400,000 Americans with Down syndrome is not credible. It is most likely that the number is closer to 250,000 – perhaps as high as 300,000 – perhaps substantially lower than 250,000.

The costs of prenatal screening services in England

In response to question from Fiona Bruce MP, the Department of Health has published estimates of the costs of prenatal screening in England.

The Chair of the UK Parliamentary Inquiry into Abortion on the Grounds of Disability, Fiona Bruce MP, recently tabled a question requesting the costs of prenatal screening for Down syndrome. In reply, the Department of Health provided estimated costs of the National Health Service Foetal Anomaly Screening Programme – which includes screening for Down syndrome. These offer a base, lower and upper scenarios at 2009/10 and 2010/11 prices for England:

Base case Lower Upper
2009-10 prices 2010-11 uplift 2009-10 prices 2010-11 uplift 2009-10 prices 2010-11 uplift
Estimates of birth used 671,058 650,000 700,000
Central coordination 1,895,735 2,000,000 1,895,735 2,000,000 1,895,735 2,000,000
Total screening strategy from the offer to the screening results 17,080,673 18,020,110 16,544,677 17,454,634 17,817,344 18,797,298
Invasive diagnostic procedure (CVS / amniocentesis) 7,802,120 8,231,237 7,557,287 7,972,938 8,138,617 8,586,241
Cost of healthy foetal loss 93,600 98,748 90,663 95,649 97,637 103,007
Cost of those T+ who terminate 486,739 513,510 471,461 497,391 507,732 535,657
Total cost of T21 screening population live births 983,759 1,037,866 952,889 1,005,298 1,026,188 1,082,628
Total screening pathway cost 28,342,626 29,901,470 27,512,712 29,025,911 29,483,253 31,104,831
Total cost, excluding continued pregnancies 27,358,867 28,863,604 26,559,823 28,020,613 28,457,065 30,022,203

In 2010/11, approximately 850 babies who would have been born with Down syndrome were not born as a consequence of the screening programme. I therefore estimate the cost of each live birth ‘prevented’ to be around £34,000.