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Imaging News

Non-invasive Prenatal testing (NIPT)

Non-invasive prenatal testing (NIPT) is a screening method for detecting certain chromosomal disorders in a developing baby. The three most common chromosomal abnormalities are Trisomy 21, Trisomy 18 and Trisomy 13, which between them occur in 1:450 live births[1]. Currently the screening tools most utilised to determine risk for these chromosome disorders is a combination of ultrasound screening to measure nuchal translucency and biochemical markers from a blood test taken from the mother. This combination offers effective screening for all major chromosomal disorders in the first trimester of pregnancy with a detection rate of about 95% and a false-positive rate of approximately 3%[2], however a positive screening test is likely to require invasive diagnostic follow up testing to confirm the result. Invasive prenatal testing – chorionic villi sampling and amniocentesis – offers a definitive answer for women, however these tests can result in a slightly increased risk of miscarriage [3]

The use of fetal DNA, which can be detected from a sample of maternal blood taken early in pregnancy is a relatively new technique with potential to improve antenatal screening by allowing earlier diagnosis without the risk associated with current invasive techniques. Non Invasive Prenatal Testing (NIPT) is a maternal blood test that can be performed from 10 weeks of pregnancy and is the most accurate screening for Trisomy 21, Trisomy 18 and Trisomy 13. NIPT provides a detection rate of >99% for Trisomy 21, 98% for Trisomy 18 and 80% detection rate for Trisomy 13[4]. NIPT has been validated for both high and low risk pregnancies and allows women to avoid the risks associated with the traditional testing options of CVS and amniocentesis. NIPT is completely risk free for the baby. The low false positive rate[5] can reduce the number of unnecessary invasive diagnostic procedures in comparison with ultrasound screening and biochemical testing, offering early reassurance. In addition the low false negative rate allows for increased early detection in affected pregnancies resulting in the opportunity for greater preparation time and choice for families and clinicians.

 

[1] Jones KL Smiths Recognisable Patterns of human malformation Jones (6th Edition) Philadelphia: Elsevier Health Sciences/ Saunders, 2006 8-87
[2] Kypros H. Nicolaides Prenatal Diagnosis 2011; 31: 7–15. Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/pd.2637
[3] Invasive testing for Aneuploidy ACOG Practice Bulletin No 88 American College of Obstetricians and Gynaecologists Obtet Gynecol 200;110 1459-67
[4] Wright, C. Cell-free fetal nucleic acids for non-invasive prenatal diagnosis, Report of the UK expert working group, PHG Foundation (2009
[5] Bianchi DW et al Genome Wide Fetal Aneuploidy Detection by Maternal Plasma DNA Sequencing Obstetrics & Gynecology 2012; 5:890-901