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Non-Invasive Prenatal Testing

In many countries, the use of maternal serum marker screening (Between 15- and 21-weeks’ gestation, a maternal serum sample is screened for alpha-fetoprotein (AFP), estriol and human chorionic gonadotropin (hCG). In addition, a fourth marker, inhibin-A, is included in some screenings), and ultrasound imaging (ultrasonography) to detect chromosome aneuploidies and other birth defects are a routine part of prenatal care in the first and/or second trimesters. However, both of these approaches suffer from high false positive rates, ranging from 2%–7%.1,2 If these tests indicate that a fetus is at increased risk of aneuploidy, invasive methods like chorionic villus sampling (CVS) or amniocentesis are recommended for diagnosis. CVS is typically offered around 10–13 weeks gestation, while amniocentesis is offered after 15 weeks. Many women are uncomfortable with invasive testing because of its physical discomfort and the associated 1%–2% risk of procedure-induced miscarriage. In recent years, a new prenatal test has entered the market and is rapidly changing the prenatal testing paradigm. Non-invasive prenatal testing (NIPT) offers an intermediate step between serum screening and invasive diagnostic testing.

  • Non-invasive prenatal testing (NIPT) is a new method of testing for common chromosomal abnormalities that can occur in a developing baby.
  • NIPT is a prenatal screening, which looks at DNA from your baby’s placenta in a sample of your blood to identify whether you’re at increased risk of giving birth to a child with a genetic disorder.
  • Noninvasive prenatal genetic testing (NIPT) is an advance in the detection of fetal
  • chromosomal aneuploidies that analyzes cell-free fetal DNA in the blood of a pregnant woman.
  • During pregnancy, there are cell-free DNA fragments (cfDNA) from both the mother and fetus in maternal circulation. It is possible to analyze cell-free DNA to detect fetal trisomies such as Down syndrome (trisomy 21).

What NIPT screens for
All NIPTs screen for the most common chromosomal disorders:
Trisomy 21 (Down syndrome)
Trisomy 18 (Edwards syndrome)
Trisomy 13 (Patau syndrome)

SAMPLE
When you’re pregnant, your blood naturally contains small amounts of fragments of your baby’s DNA.
5 ml blood from the mother can be taken into specific blood tubes. The maternal blood can be taken from week 10 of the pregnancy. Preferentially the blood is sampled in a STRECK tube. These tubes stabilize the fetal DNA
During pregnancy, there are fetal cells and cell-free DNA fragments (CFDNA) from the fetus in the maternal circulation. DNA isolated from maternal blood therefore not only contains maternal DNA but also a small amount of fetal DNA: the fetal fraction of cell-free DNA in maternal blood from week 10 on is about 10-15% of all cell-free DNA.
Collecting your blood sample for NIPT poses no threat to your baby.
Storage: at room temperature, away from direct sunlight

RELIABILITY
NIPT is more accurate than traditional first-trimester screening and much less likely to give a false positive result. That means there will be much less chance your doctor would recommend follow-up testing, such as amniocentesis.
The reliability of NIPT is very high (more than 99% for Down syndrome).
Future advances in NIPT technology promise to expand the range of conditions that can be detected, including single gene disorders. With these advances come questions of how to handle incidental findings and variants of unknown significance.

 





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