Prenatal testing for Down Syndrome

With many women becoming pregnant at an older age, I am often asked about potential risks for a pregnancy and can anything be done to improve the odds.

The most significant risk is Down syndrome and this is associated with the females age only. Many have the wrong assumption that at 35 the risk escalates, however, the risk increases right from the start with an age risk of 1/1000 at  age 20 to 1/200 at age 35 and 1/80 at age 40.

Down syndrome is a genetic condition that occurs at conception as a result of an extra chromosome. People with Down syndrome have 47 chromosomes in their cells instead of 46.

There is virtually nothing (with the exception of a specific indication for IVF) that can be done to change the risk.  There is a common misconception that if there is no previous history of Down syndrome in the family then we should be OK,  but Down syndrome is a sporadic event in pregnancy with virtually no predisposing factors – apart from maternal age.  The only way to avoid Down syndrome at the time of conception is IVF.  Pre-screening during IVF can test the embryo in the lab for Down syndrome before the embryo is transferred to the mother.

Down syndrome screening is offered to everyone during pregnancy. The long-term traditional test has been the 12-week scan or NT scan. This test uses maternal age, a blood test and a measurement at the back of babies neck  to give a risk assessment.  If the risk is high then another confirmation test is required.

The new test is very exciting. Called a NIPT test it uses amazing technology to isolate fetal DNA from the mother’s blood and test this for down syndrome. This test is highly accurate and it can be performed as early as 9 weeks into the pregnancy.