UK: Later motherhood results in rise in Down’s Syndrome pregnancies

The number of Down’s Syndrome pregnancies has risen by more than 70% over the last 20 years, University of London researchers say; but the proportion of terminations has remained constant at 92%.

The sharp rise reflects the growing number of older women becoming pregnant, when there is a higher risk, BBC News Online reports.

The number of Down’s syndrome pregnancies rose from 1,075 diagnoses in 1990 to 1,843 by 2008 in England and Wales. But despite the higher number of Down’s pregnancies, the number of Down’s syndrome babies has fallen by 1%, from 752 to 743.

This is because improved antenatal screening means more Down’s pregnancies are being spotted and more abortions are taking place. Without the improved screening, the number of babies born with Down’s would have risen by 48%, according to the study.

The proportion of couples diagnosed with a Down’s syndrome baby who decided to terminate has remained constant at 92%, say researchers at Queen Mary.

The risk of having a baby with Down’s syndrome is one in 940 for a woman aged 30. But by age 40, the risk rises to one in 85.

Joan Morris, professor of medical statistics at Queen Mary, led the research. She said:

‘What we’re seeing here is a steep rise in pregnancies with Down’s syndrome but that is being offset by improvements in screening. It was thought that these improvements would lead to a decrease in the number of births with Down’s syndrome. However, due to increases in maternal age this has not occurred.’

Professor Morris said the Down’s screening test had become more widely available over the last 20 years.

The report was published in the British Medical Journal. The abstract reads:

‘Despite the number of births in 1989/90 being similar to that in 2007/8, antenatal and postnatal diagnoses of Down’s syndrome increased by 71% (from 1075 in 1989/90 to 1843 in 2007/8). However, numbers of live births with Down’s syndrome fell by 1% (752 to 743; 1.10 to 1.08 per 1000 births) because of antenatal screening and subsequent terminations. In the absence of such screening, numbers of live births with Down’s syndrome would have increased by 48% (from 959 to 1422), since couples are starting families at an older age. Among mothers aged 37 years and older, a consistent 70% of affected pregnancies were diagnosed antenatally. In younger mothers, the proportions of pregnancies diagnosed antenatally increased from 3% to 43% owing to improvements in the availability and sensitivity of screening tests.’

The authors conclude:

‘Since 1989, expansion of and improvements in antenatal screening have offset an increase in Down’s syndrome resulting from rising maternal age. The proportion of antenatal diagnoses has increased most strikingly in younger women, whereas that in older women has stayed relatively constant. This trend suggests that, even with future improvements in screening, a large number of births with Down’s syndrome are still likely, and that monitoring of the numbers of babies born with Down’s syndrome is essential to ensure adequate provision for their needs.’

Carol Boys from the Down’s Syndrome Association said the number of abortions would be reduced if parents were better informed about Down’s syndrome. She said:

‘We realise that tests will continue to become more accurate at increasingly earlier stages of pregnancy. It is therefore even more important that families undergoing the screening process are given non-directive counselling and accurate, up-to-date information about Downs’ syndrome.’

In November 2008, the publication of statistics about the number of live births of children with Down’s Syndrome caused controversy, when it was claimed that an increase in live births was due to Britain becoming a ‘more caring society’.

Steep rise in Down’s pregnancies. BBC News Online, 27 October 2009

Trends in Down’s syndrome live births and antenatal diagnoses in England and Wales from 1989 to 2008: analysis of data from the National Down Syndrome Cytogenetic Register. Joan K Morris, professor of medical statistics, Eva Alberman, emeritus professor. British Medical Journal 2009;339:b3794

Also read:

Comment: Down’s Syndrome, live births, and statistics, by Jennie Bristow. Abortion Review, 26 November 2008