New Down’s syndrome test avoids endangering unborn baby

SCIENTISTS have developed a safe blood test that can tell a woman if her unborn baby has Down’s syndrome.

The breakthrough could allow doctors to test for genetic diseases without using invasive procedures which risk miscarriage and damage to the foetus.

Experts have been able to map the complete DNA of an unborn baby using just the mother’s blood.

They say the test could help with early diagnosis of problems and allow doctors to pre-empt whether treatments are needed immediately after a baby is born. It will also give women more choice about their pregnancy and possibly help them decide on a termination for health reasons.

One of the current ways of confirming the syndrome is amniocentesis, in which a needle is used to take a sample of fluid within the womb after 15 weeks of pregnancy.

But about one in every 100 women who has the test will miscarry as a result, according to the Royal College of Obstetricians and Gynaecologists.

Study leader Professor Stephen Quake, of Stanford University, California, said: “We are interested in identifying conditions that can be treated before birth, or immediately after.

“Without such diagnoses, newborns with treatable metabolic or immune system disorders suffer until their symptoms become noticeable and the causes are determined.”

The breakthrough could allow doctors to test for a range of genetic diseases in future, including cystic fibrosis.

A pregnant woman’s plasma, a component of blood, contains a mixture of DNA from the mother and unborn child.

The university team applied a counting method to identify individual pieces of parental DNA in chromosomes transmitted to the baby.

The researchers said their findings, published in the journal Nature, will make it easier and cheaper to diagnose genetic diseases within the first three months of pregnancy.

Babies with Down’s syndrome have an extra copy of chromosome 21, causing physical and intellectual impairments.

There will also be a relative increase in the quantity of chromosome 21 in the mother’s blood because DNA can cross the placenta from the baby to the mother.

The new test identifies and counts these fragments of DNA and detects the very small increase in chromosome 21.

Researchers were able to correctly identify all the chromosomal abnormalities in a specially selected sample of 18 pregnant women: nine cases of Down’s syndrome and two other inherited disorders caused by an abnormal number of chromosomes.

The Down’s Syndrome Association has welcomed advances in testing. A spokeswoman said: “It’s incredibly important potential parents are given accurate information on Down’s syndrome before they make a choice about whether to terminate or not.”