Delayed motherhood leads to sharp rise in Down's syndrome

Published on Monday 26 October 2009 20:54

THE number of babies diagnosed with Down's syndrome has risen sharply in the past 20 years – largely due to women delaying motherhood.

The increasing number of older mothers is behind a 71 per cent rise in the number of babies with the condition – from 1,075 diagnoses in 1989-90 to 1,843 in 2007-8.

However, the number of babies born with Down's has remained fairly static over the same period due to improved screening and subsequent abortions, the study found.

Live births of Down's babies fell 1 per cent, from 752 to 743 (or 1.10 to 1.08 per 1,000 births) over the time period.

If screening had not happened, the number of babies born with Down's would have risen 48 per cent.

Experts from Queen Mary, University of London, analysed data from the Down's register for England and Wales for the study, published online in the British Medical Journal (BMJ).

Joan Morris, professor of medical statistics at Queen Mary, who led the study, 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."

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.

Researchers found that the proportion of diagnoses among women under 37 has risen over the time period.

"Among mothers aged 37 years and older, a consistent 70 per cent of affected pregnancies were diagnosed antenatally," the study said.

"In younger mothers, the proportions of pregnancies diagnosed antenatally increased from 3 per cent to 43 per cent owing to improvements in the availability and sensitivity of screening tests."

The proportion of couples diagnosed with a Down's syndrome pregnancy who decided to terminate has remained constant at 92 per cent.

However, the actual number of abortions has risen because more babies were now being diagnosed with Down's, the study showed.

Also, many cases that would have gone on to miscarry naturally are now being diagnosed because screening is carried out earlier than even before.

Carol Boys, chief executive of the Down's Syndrome Association, 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 Down's syndrome."

BACKGROUND

What is Down's syndrome?

Down's syndrome is a genetic disorder named after British physician John Langdon Down, who identified it in 1866. It affects physical appearance and mental development.

What causes it?

Down's syndrome occurs when a baby inherits an extra chromosome at conception. Normally, people inherit 46 chromosomes. Down's syndrome is caused by a fault with chromosome number 21 – sufferers almost always inherit another copy of this chromosome.

How many people have it?

More than 700 babies are born with Down's each year. An estimated 60,000 people are currently living with Down's syndrome in the UK.

How can the it be detected?

The baby's spinal cord is examined during an ultrasound scan, and the mother's blood is tested.