At present, mothers to be are given a combined test for the syndrome at the end of the first trimester.It comprises an ultrasound known as a Nuchal Translucency (NT) scan, which measures the fluid behind the baby’s neck, a larger amount of which can indicate Down’s, and a blood test, which looks for hormones and proteins related to the syndrome.
The new procedure identifies what is known as cell-free DNA (cf DNA), tiny fragments of foetal genetic material circulating in the mother’s blood.
As well as Down’s syndrome, this DNA can be tested for other chromosomal conditions such as Edwards and Patau syndromes, both of which cause severe brain abnormalities and heart defects and mean babies rarely live beyond a year.
But a definitive diagnosis can be given only after amniocentesis, an invasive procedure that draws amniotic fluid from around the baby with a needle and syringe – and brings with it a risk of miscarriage.
Now, Carolyn and Neil Blockley, who are expecting twins, have become one of the first couples in the UK to benefit from a controversial blood test that can accurately identify Down’s and eliminate the danger of the traditional method.
She chose the screening at 12 weeks, and ten days later the results showed her babies were healthy.
But 41 per cent of those women decide not to have the test – or any other screenings available on the NHS.
Because these hormones and proteins are already higher in a multiple pregnancy, women expecting twins have only the NT scan – which is 80 per cent accurate. It was after the NT scan that doctors first alerted the Blockleys to potential problems.
Carolyn, 29, an accountant, from Pentre, Mid Glamorgan, explains: ‘They said there was more fluid than was usual around one baby’s neck.
More than 98 per cent accurate for twins and 99 per cent accurate for a single baby, the new non-invasive Ariosa Harmony test – one of a number of similar tests – requires no more than a blood sample drawn from the pregnant woman’s arm.
However, disability campaigners believe that if such a test were to become widely available, it would increase terminations of Down’s babies – nine in ten women given the news choose to have an abortion.
Down’s syndrome is one of the most common genetic causes of learning disability, and about 750 babies are born with the condition each year in the UK.