Prenatal Genetic Testing for Chromosomal Anomalies

By: Linda DeFranco

Text Purpose-to educate pregnant women about

available genetic testing-including screenings and diagnostic testing

Audience-pregnant women in an obstetrical practice at the time of their initial visit-approximately at 8-9 weeks of pregnancy

Goals-to fully inform a pregnant women of options that are available to her for detected chromosomal abnormalities including Trisomy 13 and 18, Downs Syndrome and ONTD and other fetal chromosome abnormalities

Prenatal genetic testing

ScreeningNon-invasive

First trimester ultra screen

Sequential or Quad Screen

NIPT (non-invasive prenatal testing)

Diagnosticinvasive

Amniocentesis CVS (chorionic villi sampling)

OVERVIEW OF PRENATAL GENETIC TESTING

There are different prenatal tests available to pregnant women: Screening tests vs Diagnostic testing:

SCREENING TESTS:

First trimester screen (known as an ultra screen) -11 to 13.6 weeks of pregnancy with sonogram

Sequential screen-is a blood test that is combined with the first trimester screen results -done at 16 and 21 weeks of pregnancy

Benefits of Prenatal Screening First trimester ultra screen and Sequential-non-invasive-no risk of pregnancy loss

Limitations:-not all pregnancies with trisomy 13, 18 and Downs syndrome are detected.-a false positive rate of <3%-limited to the amount of chromosome abnormalities detected

NIPS TestingNIPS (non-invasive prenatal screening) -as early as 10 weeks gestation-tests fetal DNA in maternal blood-mom has to be 35 years old at delivery (to be covered by insurance)-known as Materniti 21, Verifi, Harmony, Natera

Benefits-Detection rate is 99% for Downs Syndrome and Trisomy 18; and 90% for Trisomy 13-Low false positive rate of <1% for all Limitations-a positive result needs to be followed up with an amnio or CVS-used only for singleton pregnancies

Diagnostic testing- Invasive procedures

CVS (chorionic villi sampling)-done between 10-12 weeks-2 different methods: transcervical and transabdominal -risk for pregnancy loss=1/300

Amniocentesis (ultrasound guided)-done at 15-18 weeks Risk for pregnancy loss 1/400

Benefits of Amniocentesis and CVS:-looks directly at chromosomes -can be done with twins-CVS can be done as early as 10 weeks gestation-99.9% accurate

Limitations and Risks of Amniocentesis and CVS:-miscarriage -infection-bleeding-leaking of amniotic fluid-with CVS more cells are required

Future of Prenatal Genetic Testing

1st Trimester

Sequential

NIPS

CVS

Amniocentesis

95%

95%

90%

100%

100%

95%

95%

99%

100%

100%

91%

94%

99%

100%

100%

90%

98%

0.003

0.004

Chart----Accuracy of Prenatal Testing

Risk of Preg loss ONTD Downs Syndrome Trisomy 18 Trisomy 13

QUESTION

What testing method is the best option for a 35 year old pregnant woman with no family history of genetic abnormalities?

A. Amniocentesis

B. CVS

C. Sequential screen

D. NIPS

References

http://minnesota.cbslocal.com/2013/06/09/prenatal-tests-detect-gender-disorders-in-fetusus-early/

http://rap.northshorelij.com/contents/,DanaInfo=www.uptodate.com+first-trimester-combi...retrieved 3/6/14.

http://www.nytimes.com/2012/08/09/health/research/clinical-trial-yields-positive-results-for-new-prenatal-test.html?_r=0

https://www.youtube.com/watch?v=-nc9J4X6V4Y

North Shore-LI Jewish Medical Center-Division of Medical Genetics (2013), Manhasset, NY.

http://www.medscape.com/viewarticle/813882#2.com/viewarticle/813882#2