Noninvasive prenatal screening is also called NIPT. It is used to determine the chances that a fetus will be born with a certain genetic condition. This test looks at tiny DNA fragments that are roaming in a pregnant woman’s blood. These fragments are called cell-free DNA. They are floating freely and are not confined within cells. They differ from most DNA, which is found within the nucleus of a cell (cfDNA).
DNA in particular is set free into the bloodstream in tiny fragments. This is with just an average build of less than 200 DNA base pairs. This is because cells degrade and die.
cfDNA from the maternal placenta and maternal cells coexist in the mother’s circulation throughout the pregnancy. The placenta is a piece of tissue in the uterus. It links the mother’s blood flow with the growing fetus. These cells are discharged into the mother’s blood at various times during the pregnancy.
The DNA of the placental and the fetus is typically comparable. CfDNA analysis from the placenta gives a potential for early detection of some genetic anomalies without hurting the infant.
Purpose of NIPT Test
The most frequent application of NIPT is to test for chromosomal diseases. These are brought on by an additional or absent copy of a chromosome (aneuploidy). The main conditions that are examined by NIPT are,
- Trisomy 21 (Down syndrome).
- Trisomy 18 (produced by extra chromosome 18).
- Trisomy 13 (generated by extra chromosome 13).
- Additional or absent copies of the X and Y (sex) chromosomes.
The test’s accuracy varies. This depends on the disease,
Screening for other chromosomal diseases brought on by deleted or duplicated chromosome segments may be part of NIPT. Testing for genetic abnormalities brought on by modifications (variants) in a single gene is now being done using NIPT. Researchers anticipate that NIPT will be accessible for a wide range of genetic diseases. This will happen as technology advances and the genetic testing cost declines.
When is the NIPT Test Recommended?
NIPT can be done sooner compared to other prenatal screening or diagnostic tests. This can start once your pregnancy has reached 9 weeks. Comparatively,
- The quad screen is finished between weeks 14 and 22.
- Nuchal translucency screening is performed between weeks 11 and 13.
- CVS is performed between weeks 10 and 13.
- Amniocentesis is typically carried out between weeks 16 and 18.
Only the pregnant mother must have her blood drawn and the fetus is not at risk. So NIPT is regarded as non-invasive. NIPT is a screening test. Therefore it cannot conclusively determine whether or not a fetus has a genetic disorder. This test can only provide an estimate of whether there is an increased or decreased chance of developing specific illnesses.
In some circumstances, NIPT findings show a false positive or heightened risk for a genetic defect when the fetus is truly unaffected. It may also show a false negative when the fetus is directly impacted. The NIPT test has the potential to identify a genetic disorder in the mother. This is because it examines both maternal and fetal cfDNA.
There must be sufficient fetal cfDNA in the mother’s circulation to identify fetal chromosome abnormalities. The proportion of maternal plasma’s cfDNA is known as the fetal fraction. It generates from the placenta. Normal fetal percentage occurs in the 9th week of pregnancy when it is larger than 4%. Low fetal fractions could make the test ineffective or cause a false negative. These can be caused by,
- Fetal anomalies.
- Sampling errors.
- Maternal obesity.
- Screening too early in the pregnancy.
Methodology of NIPT Test
The NIPT is carried out with a straightforward maternal blood sample. So neither you nor your baby is at risk. Your blood will be taken and delivered to a particular lab. The technicians there will examine the results.
Within 8 to 14 days, your results will be delivered to your doctor (this is the practice in most cases).
Risk factors of NIPT
The NIPT is typically provided to women depending on the protocols and recommendations of their OB-GYN even if it is optional. However, several risks can persuade your healthcare specialists to strongly advise it.
Some of these risk variables are –
- A personal or familial history of a pregnancy with a chromosomal abnormality.
- The mother’s age is 35 or above at the time of delivery.
- A chromosomal anomaly that is either maternal or paternal
It is acceptable to take the time necessary to decide what is best for you. This is because deciding to undergo the NIPT test is a very personal decision. If you are struggling, think about talking to your doctor or a genetic counsellor. They can better understand your worries and help you.
Accuracy of NIPT
According to research, NIPT can accurately identify by 97 to 99%, a person’s chance of –
- Down syndrome.
- Edwards syndrome.
- Patau syndrome.
When compared to normal first-trimester blood screens that check for hormones and specific proteins in the mother’s blood, NIPT produces fewer false alarms for these illnesses.
But these tests are far less reliable when it comes to foretelling uncommon genetic diseases like,
- DiGeorge syndrome.
- 1p36 deletion.
- Cri-du-chat syndrome.
- Wolf-Hirschhorn syndrome.
- Turner syndrome.
- Prader-Willi syndrome.
Conclusion
Noninvasive Prenatal Testing provides a dependable tool for elective screening. This helps to determine the genetic risk of a fetal chromosomal abnormality in the first trimester of pregnancy,
When a pregnant woman has certain genetic condition risk factors, it is frequently and strongly advised. The test is not diagnostic. But it can still be a useful step in learning more about your baby’s health.
The NIPT is ultimately up to you to decide. Anyone thinking about taking it may also have emotional effects. Speak to your dependable OB-GYN if you have any queries or worries regarding the NIPT screen for advice and assistance.
