Non-Invasive Prenatal Testing (NIPT) Faetsheet

Non-Invasive Prenatal Testing (NIPT) Faetsheet Introduction NIPT, which analyzes cell-free letal DNA circulating in maternal blood, is a new option in the prena:al screening and testing paradigm for trisomy 21 and a few other fetal chromosomal aneuploidies. (For more information about current screeningltesting options, see Background.)

NIPT Test Characteristics Genetic testing using cell-tree fetal DNA DNA from the fetus circulates in maternal blood. Unlike intact fetal cells

All laboratories offering NIPT report on trisomy 21 and triso-

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some sex chromosome abnJr-

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provide any other genetic infor-

ly in the general screening/testing for trisomy 21

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NIPT appropriate. prenatal paradigm

tution of the mother or fetus

Detection rate for

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trisomy 21

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Al least 99% ct all pregnancies with trisomy 21 can

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lating cell.free letal DNA (ceffDNA) results from the breakdown 01 letal

Fetal DNA detected during a pregnancy, therefore, represents DNA trom

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in maternal blood, which can persist for years after a pregnancy, circu-

cells (mostly placental) and clears trom the maternal system within hours.

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Although only about 10-15% of the cell-tree DNA circulating in maternal blood is from the fetus. it can be detected and measured. Quantitative differences in chromosome fragments in maternal blood can be used to distinguish fetuses affected with trisomy 21, and a tew other fetal aneuplodies, from those that are not affected.

He false-posi:ive rate is approximately 0.2%, mean. ing 1 in about SOD unaffecte::t pregnancies are reported as 'positive' or 'consistent with' trisomy' 21. For that reason, it is recommended that CVS or amniocentesis be consid.

When NIPT is perfonned

ered after an abnormal result to confirm the presence of a chromosome

Testing can be done any time a'ter 10 weeks; typically i1is done abnormality .• between 10-22 weeks. Results can take a week or more.

Maternal indications for NIPT

Detection rate for trisomy 18 He detection rate for trisomy 18 may be similar to that for trisomy

NIPT technologies have been validated in singleton pregnancies at high 21; approximately 99% 01 plegnancies with trisomy 18 will be detected risk for trisomy 21 due to: by NIPT. About 1 in 100 pregnancies with trisomy 18 will be missed on advanced maternal age screening. an abnormal serum screen He false-posi:ive rate is also similar to trisomy 21. About 1 in 500 pregpersonal or famil~' history of aneuploidy nancies unaffected with trisomy 18 will have an abnormal, or positive, abno~mal ultrasound result, so confirmatory testirg is recommended." At least one laboratory wilt accept samples lhat do not meet these high risk criteria. Additionally, at least one laboratory offers the test in twin pregnancies, and another for Turner syndrome (monosomy X) when t~e fetus presents with a cystic hygroma. Contact individual laboratories for additional information.

Detection of trisomy 13 and sex chromosome

abnonnalities

H,ere is less confidence ir NIPT as a screen for trisomy 13 due to technical issues and the infrequency of the condition. Detection rates between 79-92% have been reported, meaning between 8 to 21 out of 100 pregnancies with affected fetuses •••• ill be missed. The false-positive

Risk

rate may be about 1%. so 1 out of 100 unaffected pregnancies may be

The testing is non-invasive, involving a maternal blood draw, so the positive lor trisomy 13, so confirmatory testing is recommended.' pregnancy is not put at risk for miscarriage 01 other adverse outcomes Some laboratories may report results for sex chromosomes abnormal. associated with invasive testing procedures. ities. If testing for sex chrorT()some abnormalities is desired, contact the

NIPT Detection Rate and Accuracy At present. NIPT provides information about specific fefal aneuploidies.

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An alternative to screening is invasive prenatal diagnosis by chorion-

Pathway for Fetal Trisomies, Journal of Managed Care Medicine,

ic villus sampling (CVS) or amniocentesis which directly assesses the

2012;15:34 - 41.

chromosome constitLtion of the fetus through cells from the pregnancy. The advantage is the diagnostic certainty at cetecting trisomy 21, 18, and

Norton ME, Brar H, Weiss J, et al. Non-Invasive Chromosomal

13. In addition, testing fetal cells and the amniotic fluid may allow for the

Evaluation (NICE) Study: results of a multicenter prospective cohort

detection of other chromosome abnormities, genetic conditions, or open

study for detection of fetal trisomy 21 and trisomy 18. American Journal

neural tube defects. The downside is that these procedures are associ-

of Obstetrics & Gynecology 2012;207:137.el-8

ated with a measurable risk of a procedure-related

miscarriage or other

Palomaki, G. E., Deciu, C., Klola, E. M" et al. DNA sequencing 01 mater-

adverse pregnancy outcome.

nal plasma reliably identifie:: trisomy 18 and trisomy 13 as well as Down

Publication Acknowledgements

syndrome: an international collaborative study. Genetics in Medicine

Developed under an educational grant from Sequenom. Copyright 2012

2011 :14:296-305.

by the National Coalition for Health Professional Education in Genetics Palomaki, G. E., Klola, E. M., Lambert Messerlian, G. M., et a1. DNA and National Society of Genetic Counselors. This resource is for informasequencing of maternal pla::ma to detect Down syndrome: an internationtional and educational purposes only. al clinical validation study. Genetics in Medicine 2011; 13:913.920.

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