Noninvasive prenatal testing (NIPT), is a screening test for determining the risk of certain chromosomal abnormalities in the fetus. NIPT is commonly used for chromosomal disorders that are caused by the presence of an extra (triploidy) or missing copy (aneuploidy) of a chromosome.
Common Abnormalities Are:
- Down syndrome (trisomy 21, an extra chromosome 21),
- Trisomy 18 (caused by an extra chromosome 18),
- Trisomy 13 (caused by an extra chromosome 13),
- And extra or missing copies of the X chromosome and Y chromosome (the sex chromosomes).
- It can be used to identify even sections of DNA that are deleted or duplicated.
How is the test conducted?
DNA is the genetic material that is found inside the nucleus of a cell. During pregnancy, small amounts of fragments of DNA are found floating in the pregnant woman’s blood. These fragments are free-floating and not inside the cell and so are called cell-free DNA (cfDNA).
The mother’s bloodstream contains a mix of cfDNA that comes from her cells and cells from the placenta. The DNA in placental cells is usually identical to the DNA of the fetus. NIPT involves testing this placental DNA that is free-floating in the mother’s blood and looking for chromosomal abnormalities.
NIPT is noninvasive as it requires only a sample of maternal blood to be collected.
A screening test will not give a definitive answer about whether a fetus has the abnormality or not but will give only a risk estimate whether the fetus has the condition or not.
If the risk is high then further confirmatory tests will be required. The confirmatory tests are amniocentesis and chorion villous sampling. These are invasive tests and have a small risk of miscarriage but will give a definitive answer whether the fetus is affected or not.
Noninvasive Prenatal Testing (NIPT) is done at 10 weeks because it is at this time that there is enough fetal DNA in the mother’s circulation. The test is suitable for all single and identical twins’ pregnancies, and IVF, egg donor, or surrogate pregnancies.
The Noninvasive Prenatal Testing (NIPT) is not suitable for:
- Multiple pregnancies (greater than twins)
- If the mother has cancer, a chromosomal or genetic condition (including Down’s syndrome).
- If the mother has undergone a blood transfusion in the last 3 months, had transplant surgery, immunotherapy, or stem cell therapy.
It is advisable to discuss with the gynecologist and decide regarding all the screening tests that you will require and the correct timing for them.
It is important to understand the aim of the tests, the limitations, the risks involved, and the options you have in case the results are suggesting an abnormality. After a thorough discussion, you can choose whether you would like to do it or not.
