The number of Down’s syndrome pregnancies has risen sharply over the past 20 years, largely because of an increase in older women trying to have children, research suggests.

A study of Down’s syndrome trends by scientists from Queen Mary, University of London, shows that antenatal and postnatal diagnoses have increased by 71 per cent, from 1,075 in 1989 to 1,843 last year.

But the number of babies born with Down’s has remained fairly static over the same period. Live births of Down’s babies fell by about 1 per cent, from 752 to 743, over the same period.

If screening had not taken place, the number of babies born with Down’s syndrome would have risen 48 per cent, the researchers concluded.

The team said that they were surprised that the number of births had not dropped even more. They also observed that rates of screening among pregnant women over the age of 37 had not increased, despite the improved diagnostics.

Experts from the university analysed data from the National Down Syndrome Cytogenetic Register for England and Wales since it was set up in January 1989. The paper is published today online by the British Medical Journal. The register holds more than 26,000 antenatal and postnatal diagnoses of Down’s syndrome made by all cytogenetic laboratories, which analyse chromosomal abnormalities, since 1989. This accounts for about 93 per cent of all diagnosed Down’s births and pregnancy terminations.

Down’s syndrome occurs when a baby inherits an extra chromosome, creating a genetic imbalance that affects an individual’s physical and mental characteristics. It is estimated that there are about 60,000 people with Down’s syndrome in Britain.

Joan Morris, Professor of Medical Statistics at Queen Mary, University of London, who led the study, said that the steep rise in pregnancies was 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.

“Major improvements to the Down’s screening test and the fact that it has become more widely available over the last 20 years, means that we’re picking up more Down’s pregnancies.”

She added that because older women have a far greater chance of having a baby with Down’s — the risk for a 40-year-old mother is 16 times that for a 25-year-old mother — more research was needed to find out why about 30 per cent of older women decide not to be tested. “It is important to ascertain whether the decision is an informed one and, if not, to address the lack of information.”

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

Researchers found that the proportion of cases diagnosed antenatally in women under 37 has risen over the time period, from 3 per cent to 43 per cent. However, among older women, a consistent 70 per cent of affected pregnancies were diagnosed antenatally.

One woman, who chose to have a termination after a Down’s diagnosis, said: “Some people probably think, how could you do that, how do you live with it? But it was one of those choices I had to make. I see parents in their sixties and seventies with Down’s children, and I think, no, I made the right one.”

The woman, then 33, learnt that her fourth child would be born with Down’s syndrome when she was 22 weeks’ pregnant. “Everybody says they know what they’d do in that situation. But you don’t. You never know until it happens to you.”

The authors conclude that as more women are having children later in life, continued monitoring of the numbers of Down’s babies is essential to ensure adequate provision for their needs. Professor Morris added that further research was at risk because funding for the national register, provided by the Healthcare Quality Improvement Partnership, was guaranteed only until March 2010.

Down’s affects people in different ways. In the 1950s, many with Down’s did not live past the age of 15 but medical advances mean that life expectancy is now 60 to 65. Around 40-50 per cent of children will have a heart defect from birth, with 30 per cent of these cases needing immediate surgery.

Around half of sufferers will experience problems with hearing and sight, while they are also more susceptible to infections and are more likely to develop leukaemia and dementia in later life.

Testing for Down’s syndrome takes place before the 14th week of pregnancy. The common “triple” test estimates the risk by looking at the baby’s spinal cord, the results of a blood test for chemicals in the mother’s blood and the mother’s age. Further tests can be carried out if there is a high chance the baby has Down’s. These are invasive and can trigger a miscarriage.

Researchers at the University of Oxford recently announced the results of a clinical trial of a test that virtually eliminates the risk of Down’s for patients undergoing IVF.

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