Non-Invasive Prenatal Testing is 99 per cent accurate when screening for Down's syndrome

When Doris Chan's prenatal test results showed that her 12-week-old fetus had a one in 125 chance of having Down's syndrome, she was in shock. At 35 years old, Chan (whose name has been changed for reasons of patient confidentiality) was stressed by her biological clock and had previously suffered two miscarriages.

"We started to ask ourselves hard questions, like 'Do we keep the baby?' and 'What kind of changes do we make to our lives?'" says Chan.

Traditionally, the next step is to confirm the diagnosis through an amniocentesis or chronic villus sampling (CVS). Both procedures are invasive - a needle is inserted in the woman's uterus to draw out either amniotic fluid (amniocentesis) or tissue from the placenta (CVS) - and carry a risk of miscarriage of up to one in 100.

Chan wasn't too keen on either procedure as she didn't want to risk losing another baby. Her doctor suggested Non-Invasive Prenatal Testing (NIPT) instead, a relatively new DNA test that has shown in studies to be more than 99 per cent accurate in screening for Down's syndrome, Edwards syndrome and Patau syndrome.

A blood sample was taken and a week later she got a call from her doctor: the NIPT result was negative. "It was a huge relief," says Chan, who is now 32 weeks into her pregnancy.

The number of women in Hong Kong opting for NIPT has increased steadily since its introduction worldwide in 2011. At The Women's Clinic in Central, nearly 80 per cent of antenatal women choose to have NIPT says obstetrician Dr Charas Ong Yeu-theng.

At Central Health Medical Practice, about 60 per cent of pregnant women have the test, says obstetrician Dr Lucy Lord.