The ACMG (American College of Medical Genetics and Genomics) and ISPD (International Society of Prenatal Diagnosis) recently released important statements on NIPT (non-invasive prenatal testing). These help to clarify any doubts and misconceptions about this form of prenatal screening for chromosomal abnormalities.
We have summarized their findings to make it easier for you.
- ACMG specifically refers to NIPT as NIPS (non-invasive prenatal screening) and states that these tests are advanced ‘screens’ to identify pregnancies at risk for commonautosomal aneuploidies (e.g., trisomy 21, 18, and 13)
- NIPS is not diagnostic and confirmatory testing (chorionic villus sampling oramniocentesis) is recommended, especially for women seeking a definitive diagnosis.
- There is a possibility of false-positive screening results, which may be due to confined placental mosaicism or theoretically a ‘vanishing twin’.
- Maternal cfDNA screening is an emerging technology that can provide highly effective prenatal screening for Down syndrome, trisomy 18, and possibly trisomy 13 in high risk women. This is suggested for high risk women based on
- Maternal serum screening
- Maternal age
- Presence of an ultrasound abnormality suggestive of trisomy 21, 18 or 13
- Family history of a chromosome abnormality that could result in full trisomy 21,18 or 13
- History of a previous pregnancy/live birth with trisomy 21, 18 or 13
- Efficacy in low-risk women has not yet been fully demonstrated and there is currently only limited data to suggest the test failure rate will not be appreciably higher. The false-positive rate also appears to be comparable.
- Women interested in such testing should receive detailed counseling explaining the benefits and limitations of the test.
- They must be informed that these tests are still under clinical development. Information that must be provided to the pregnant woman includes:
- The testing currently available is mostly focused on the detection of fetal trisomies 21, 18, and 13
- Although detection rates are high, the test does not detect all cases of fetaltrisomy 21, 18 and 13
- Although false-positive rates are low, there will be occasional false-positive results therefore women with positive cfDNA screening results should be offered confirmatory fetal chromosome analysis either through an amniocentesis or CVS.
- For some women the cfDNA screening test may not be informative and these patients may then need to consider invasive testing.
- In particular, women with an increased body mass index are at high risk of test failure or an inconclusive result. For late gestational age women, there may be insufficient time for a repeat screening test and/or invasive testing.
Dr. Jorge L. Gomez earned his Medical Degree in 1990 at Central Del Caribe University in Bayamon, Puerto Rico. Following residency in Obstetrics and Gynecology at Bronx-Lebanon Hospital center in the Bronx, NY (1990–1994), he completed additional fellowship training at New York University Medical Center NY, specializing in Maternal Fetal Medicine (1994-1996). After his fellowship in 1996 he joined South Florida Perinatal Medicine. Dr. Gomez is Board certified in OBGYN and Maternal Fetal Medicine. From 2003–2007 He was a reviewer for the American Journal Of Obstetrics and Gynecology.