A non-invasive prenatal test (NIPT test) is an advanced screening diagnostic test using DNA in the mother's blood to estimate the increased risk of a fetus being affected by chromosomal disorders such as Down’s syndrome (trisomy 21), Edwards' syndrome (trisomy 18) and Patau’s syndrome (trisomy 13) along with some additional genetic conditions. There are many different NIPT screens on the market, but the majority will screen for these three syndromes along with some additional conditions such as sex chromosome and autosomal aneuploidies. Edwards’ and Patau’s syndrome are chromosomal conditions that are much rarer than Down’s syndrome but are very serious and many affected babies die before or soon after birth. Trisomies occur when three, instead of the usual two copies of a chromosome are present.
How does NIPT work?
From 10 weeks gestation, a small blood sample is taken from the mother’s arm and sent to a local laboratory for a genetic screening analysis with the IONA® or IONA® Care tests. 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. This DNA is extracted from the pregnant mother’s blood 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. IONA® Care additionally detects the small changes in the DNA ration when a Sex Chromosome Aneuploidy (SCA) or Autosomal Aneuploidy (AA) is present. The IONA® analysis software for analysis calculates the relative amounts of the chromosomes of interest to produce a risk score in order to predict the presence of a trisomy or aneuploidy. 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) for Down’s, Edwards’ or Patau’s syndrome can be used instead) to calculate the probability of the fetus being affected.
Traditional Prenatal Screening
“Traditional” prenatal screening and genetic testing offered during the first trimester of pregnancy is currently called the Combined Test (CT) as it combines maternal age, an ultrasound scan to measure the nuchal translucency (NT), with a maternal blood test for serum markers. This is an ultrasound scan to measure the nuchal translucency (NT), combined with a blood test. This is less accurate than NIPT, detecting only about 80%–90% of babies with Down’s syndrome and present a 5% false positive (FP) rate [1, 2].
The IONA® test
The IONA® test has a higher detection rate (>99%) than the Combined Test. The IONA® test is also better able to exclude false positives. False positives occur when the test results reports the baby is at a high risk of having Down’s syndrome but is actually unaffected. The IONA® test is much better at ensuring the babies reported as high risk are truly high risk. This allows the clinician to only refer the mother for an invasive test when it is highly likely the baby is affected. This means fewer pregnant women will undergo unnecessary invasive follow-up procedures such as an amniocentesis or CVS which can be stressful, painful and may carry a small risk of miscarriage.