Ch. 17 Genetics in Medicine: Prenatal Screening and Diagnosis

Flashcards about prenatal screening and diagnosis, covering topics such as screening for neural tube defects and aneuploidies, noninvasive prenatal screening, prenatal diagnosis methods, and genetic testing.

What is prenatal screening/ what are they able to detect?

Testing in pregnancies - test for common birth defects:

• chromosomal aneuploidies,

• neural tube defects

• other structural anomalies.

What is a major advancement in noninvasive prenatal screening?

Sequencing of cell-free DNA in maternal blood.

What is the goal of prenatal screening

To identify pregnancies that should be offered prenatal diagnostic testing.

1. What are AFP levels used to detect?

2. What is the difference between AFAFP and MSAFP?

1. AFP levels are used to detect neural tube defects and certain chromosomal conditions, assessing fetal development and health with a blood test

2. MSAFP (Alphafetoprotein in Maternal serum)

3. AFAFP (Alphafetoprotein in Amniotic Fluid)

Describe the three first trimester procedures used to test aneuploidies

• Pregnancy associated protein (PAPP-A) - decreased in trisomies

• Human Chorionic Gonadotropin (HCG) - elevated in Trisomy 21, depressed in others

• Ultrasound to measure nuchal translucency (NL) - increased in trisomies and monosomies

When does a pregnant woman's serum contain fetal DNA that is floating freely?

After 7 weeks of gestation - related to NIPS

1. Is Noninvasive Prenatal Screening (NIPS) a screening test or diagnostic test?

2. What is it used for?

1. A screening test, not diagnostic.

2. Analysis of cell-free fetal DNA and can be used to genotype the RH locus and determine fetal sex

What factors of pregnancy indiciate “elevated risk”?

• birth of a child with a previous disease

• family history of the disorder

• positive parental carrier test

• positive prenatal screening test

*uses an invasive test - chorionic villus sampling or amniocentesis

Describe Ultrasound and how it is useful in prenatal screening

• non-invasive screening and used to detect malformations or other anomalies which may/may not be associated with aneuploidy

• useful for single gene disorders that do not have a definitive DNA based testing

• Can test for multifactorial disorders - neural tube defect and congential heart defects

What are some indications for prenatal diagnosis by invasive testing?

Previous child with genomic imbalance

structural chromosome or genome abnormality in a parent

family history of genetic disorder

increased risk based on screening tests

Describe chorionic villus sampling and the pros and cons of using it in prenatal screening

• Chorionic villus sampling (CVS) is an invasive procedure that involves taking a sample of placental tissue to test for genetic abnormalities

• Pros: results determined earlier in pregnancy

• Con: slight increase risk of fetal loss

What is amniocentesis?

Inserting a needle transabdominally into the amniotic sac to obtain a sample of amniotic fluid.

U/S is used prior to, to see position of fetus

For fetal chromosome and genome analysis

What is preimplantation genetic diagnosis (PGD)?

Testing during IVF to select embryos free of a specific genetic condition before transfer to the uterus.

How is diagnosis made for preimplantation genetic diagnosis(PGD)?

PCR, FISH, or chromosomal microarray (CMA).

What test can be used to rapidly test for aneuploidy when needed?

FISH (fluorescent in situ hybridization).

What test should be the 1st-line test when a fetal abnormality is found on ultrasound?

Chromosome microarray analysis.

What are typical prenatal screenings able to detect?

• chromosomal aneuploidies

• neural birth defects

• other structural anomalies

Tends to be non-invasive such as blood sampling

describe the four second trimester procedures used to test for aneuploidies

Second trimester screening is a quadruple screen:

• HCG - elevated in trisomy 21, depressed in other trisomies

• Maternal serum AFP - depressed

• Unconjugated estriol - depressed

• Inhibin A - elevated in trisomy 21, unaffected in other trisomies