Non invasive prenatal testing is any type of prenatal testing that is not invasive. Invasive tests include amniocentesis and chorionic villus sampling (CVS). In recent years, the use of circulating cell free DNA (ccfDNA) has been given the acronym NIPT for non-invasive prenatal testing. Technically, however any of the available options that does not take a direct sample from around the baby (amniotic fluid or cells from the placenta) is considered NIPT.
First trimester screening – uses a combination of ultrasound and pregnancy hormones to determine risks of down syndrome. Additional benefits include that there is a direct visual evaluation of fetal development and the pregnancy hormones obtained can provide information on placental function, and risks of developing preeclampsia. In experienced hands, detection rates for down syndrome are as high as 90%. Any positive result should have a follow up with additional testing, either ccfDNA, or invasive testing and a detailed ultrasound.
Circulating cell free DNA – This uses fetal cells obtained from maternal blood to evaluate for down syndrome. It is an evolving technology with a very high detection rate for down syndrome (up to 99%). It is also useful in identifying other chromosome abnormalities. The advantage is the high detection rate for down syndrome. The disadvantage is that it does not provide information on the developing fetus if no ultrasound is done in combination. Additionally, some of the more rare disorders it tests for have a lower detection rate. For any positive result, the positive predictive value can be calculated. Invasive testing is offered for all positive results. Positive predictive values can be calculated.
Quad screening – This is an older method of screening for down syndrome. The detection rate is around 80%. Given the availability of first trimester screening for most patients and ccfDNA, the use of the Quad screening has become limited. The advantage of the test is that is easily done.