Non-invasive prenatal testing (NIPT), also known as non-invasive prenatal screening (NIPS), is an advanced genetic screening test used during pregnancy to assess the risk of certain genetic conditions or chromosomal abnormalities in the fetus such as Down syndrome, Edwards syndrome and Patau syndrome. NIPT/NIPS is done using a simple blood test of pregnant women which analyzes the fetal DNA circulating in their bloodstream, where about 20 ml of the mother’s blood is taken for testing and the result is available in about 10 days.
In an interview with HT Lifestyle, Dr Chetna Jain, director, department of obstetrics and gynaecology at Cloudnine Group of Hospitals in Gurgaon Sector 14, said, “NIPT/NIPS has revolutionised the care of pregnant women. It analyses cell-free foetal DNA that is circulating in the mother’s blood. This test can be done from 10 weeks of pregnancy. Traditionally, the double marker was used as a screening test for Down syndrome as a first trimester serum (blood) screening between 11 and 13 weeks of pregnancy. It has a detection rate of around 80%. When combined with the nuchal scan, the detection rate is around 90% with 5% being false positives. This means that around 5% of women will test positive even if their baby is normal and will need further invasive investigations
Objective:
Dr. Chetna Jain explained that NIPT/NIPS is mainly used to check for normal chromosomal conditions in the embryo, specifically –
- Trisomy 21 (Down syndrome): It is caused by an extra copy of chromosome 21.
- Trisomy 18 (Edwards syndrome): It is caused by an extra copy of chromosome 18.
- Trisomy 13 (Patau syndrome): It is caused by an extra copy of chromosome 13.
- Sex chromosome abnormalities: NIPT/NIPS can also test for conditions such as Turner syndrome (monosomy X) or Klinefelter syndrome (XXY).
how it works:
Dr Chetna Jain explained, “During pregnancy, a small amount of fetal DNA is naturally released into the bloodstream of pregnant women. NIPT/NIPS uses a maternal blood sample to isolate and analyse this fetal DNA. By examining the relative amounts of different chromosomes or specific genetic markers, the test can predict the risk of certain chromosomal abnormalities.”
Benefit:
- Non-invasive: There is no risk of miscarriage with NIPT/NIPS, as it only requires a blood sample from a pregnant woman.
- high accuracy: NIPT/NIPS has a high detection rate for common chromosomal conditions, especially Down syndrome, and has a low false positivity rate compared with traditional screening tests such as maternal serum screening (e.g., quad screen).
- Early detection: NIPT/NIPS can be performed as early as 9–10 weeks of pregnancy, providing quicker results than other diagnostic tests such as amniocentesis or chorionic villus sampling (CVS).
How accurate is NIPT/NIPS?
Dr. Chetna Jain replied, “NIPT is highly accurate. The detection rate is 99% for Down syndrome, 96% for trisomy 18 and 91% for trisomy 13. NIPT has the highest detection rate of any non-invasive test. Combined evaluation with ultrasound and NIPT significantly reduces the need for invasive procedures like amniocentesis.” She elaborated –
- False positive NIPT: The accuracy of NIPT for Down syndrome is 99%. The chances of a false positive are rare. More data is needed to give an accurate figure.
- False negative NIPT in detecting autosomal chromosome conditions such as Down syndrome is very rare, about 0.02% to 0.2%.
Risks associated with NIPT:
According to Dr. Chetna Jain, there is no risk of miscarriage in NIPT. The risk of miscarriage in CVS procedure is 0.5 to 1%. The risk of miscarriage in amniocentesis is 0.25 to 0.5%.
Limitations and Considerations of NIPT:
- NIPT has low sensitivity for twin pregnancies. It is not available for triplets or higher order multiple pregnancies.
- It is not available for other genetic conditions such as cystic fibrosis.
This may give false positive or false negative results. - This facility is not available to women who themselves suffer from Down syndrome, balanced chromosomal translocation or cancer.
- Women who have had an organ transplant or blood transfusion in the past four months cannot do so.
NIPT cannot test for all chromosomal conditions. Not all NIPT panels test for conditions involving the sex chromosomes, such as Turner’s, Klinefelter’s, and triple X syndrome. - Since NIPT is a screening test, all positive cases are recommended to be confirmed with a diagnostic test, which is CVS or amniocentesis. A pregnancy cannot be terminated based on a screen positive NIPT result.
Who should undergo NIPT?
Dr. Chetna Jain explained, “NIPT is offered to all pregnant women from 10 weeks in the United States, even low-risk populations. It should be offered and considered by women whose maternal age is over 35 years, ultrasound shows abnormal findings, or there is a family or personal history of chromosomal abnormality.”
boundaries:
- Any pregnant woman undergoing NIPT should understand that although it is the best screening test available so far, it can have false positive and false negative results. Any abnormal result will require further invasive investigation by amniocentesis or CVS.
- It is important for prospective parents to have adequate information about NIPT during the early stages of pregnancy. With advances in technology, more conditions will be identified by non-invasive testing in the future. As of today, NIPT is outperforming all non-invasive screening tests.
Things to consider:
- NIPT/NIPS results should be interpreted by a qualified healthcare provider, who can discuss the implications of positive or abnormal findings and guide further diagnostic testing if needed.
- NIPT/NIPS is optional and is offered to pregnant individuals based on their individual preferences and risk factors.
In summary, NIPT/NIPS is a valuable prenatal screening tool that provides a non-invasive assessment of fetal genetic risk for common chromosomal conditions during pregnancy. It provides early and accurate information that can guide subsequent prenatal care and decision making.
