From 10 weeks gestation a small blood sample is taken from the mother’s arm and sent to a local laboratory for analysis with the IONA® test. During pregnancy, the placenta leaks cell-free DNA which circulates in the maternal bloodstream. As a result, a maternal plasma sample contains a mixture of placental and maternal circulating DNA. The DNA from the mother’s blood is extracted and the test is performed on this small amount of DNA.The IONA® test directly measures the amount of cell-free DNA and can detect small changes in the DNA ratio between the maternal and placental-fetal cell-free DNA when a fetal trisomy 21, 18 or 13 is present.
The IONA® Software for analysis calculates the relative amount of chromosomes 21, 18 and 13 to produce a risk score to predict the presence of a trisomy. This figure is then combined with the prior risk (by default this is the mother’s age but the result of the First Trimester Combined Test (FTCT) can be used instead) to calculate the probability of the fetus being affected.