Screening for Down syndrome

A baby is something that you carry inside you for nine months, in your arms for three years and your heart until the day you die. A healthy baby is a priceless gift from the almighty.

Down's syndrome occurs in about 1 in 600 pregnancies all over the world. People with Down's syndrome have an extra chromosome and these manifests as varying levels of mental and physical retardation. Down's syndrome happens at conception, when the genetic bundles from the egg and the sperm fuse. Down's syndrome is not an inherited condition.

In most cases it happens by chance. Any women can have a baby with Down's syndrome and therefore there are screening tests for this. The risk of having a baby with Down's syndrome varies with mother's age; as the mother's age increase, the risk increases, 70% of babies with Down's Syndrome are born to younger mother (below 35 yrs) and therefore screening is offered to all women.

A new combination of blood tests and ultrasound can detect fetuses with Down's syndrome at 12 weeks into pregnancy and more accurately offering mothers to be more peace of mind and more time to decide on the way forward.

This is a screening option at first trimester commonly referred to as OSCAR (One Stop Clinic for Risk Assessment) or NT (Nuchal Translucency) Scan. It is a test that is offered to all pregnant women as an earlier and more accurate method of screening for chromosomal abnormalities, in particular to Down's syndrome, Trisomy 21. The risk assessment is done by a combination of maternal age, fetal length, fetal NT and serum biochemistry at 11 to 13 weeks 6 days into pregnancy. A composite risk assessment will then be computed.

The combination of two maternal blood test (PAPP-A and Free beta hCG) + ultrasound + maternal age = correctly identifies 90% of the fetus with Down's syndrome and yields results at about 12 weeks. The advantage of nuchal scanning over just biochemical blood profiling or ultrasound alone is mainly the reduction in false positive rates.

When all the indicators together show a high probability of Down's syndrome, expectant mother can choose to have a definitive and invasive test — CVS and or amniocentesis.

According to the American College of Obstetrics and Gynaecology, all women whatever their age, have a small risk of delivering a baby with physical and intellectual disability. The NT scan will help to estimate the risk of fetus having Down's syndrome and other major structural chromosomal abnormality more accurately than maternal age alone.

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