Prenatal Screening

Question 1

What is the goal of a screening test?

Answer 1

To identify individuals with an unrecognized disease. To sort out those who probably have the disease from others who dont.

Question 2

What is a critical value/cut-off?

Answer 2

A chosen value at which everyone at or above are considered ‘Screen Positive’

Question 3

What happens if someone is Screen Positive?

Answer 3

Individuals are offered diagnostic testing to determine if they have the condition.

Question 4

What is the test sensitivity?

Answer 4

The test’s ability to correctly identify those with the disease.

Question 5

What is the test specificity?

Answer 5

The test’s ability to correctly identify those without the disease

Question 6

What is the relationship between sensitivity and specificity?

Answer 6

They are in an inverse relationship to each other; You want a balance between the two.

Question 7

What if there was a test that was 100% sensitive?

Answer 7

All affected individuals would be detected; Will have more false positives.

Question 8

What if there was a test that was 100% specific?

Answer 8

All unaffected individuals will be identified; Will have more false negatives.

Question 9

What is the relationship between maternal age and aneuploidy?

Answer 9

If the mother is older than 35, there is an increased risk for aneuploidy.

Question 10

Give example of ethnicity based screening.

Answer 10

Minorities are screened for sickle cell and thalassemias; Ashkenazi Jewish are tested for Tay Sachs, CF, Canavan disease and Familial Dysautonmia.

Question 11

What if someone tests negative in a carrier screening test?

Answer 11

A negative carrier test result reduces the risk of the condition but does not eliminate it.

Question 12

What are the tests done only during pregnancy?

Answer 12

Done at 15-23. AFP, Quad, First Trimester, Full integrated, Sequential, Serum Integrated.

Question 13

Describe AFP test

Answer 13

Done 15-23 weeks. Elevated value increases risk of dorsal and ventral wall defects (anancephaly, spina bifida)
Low levels of AFP suggest increased risk of Down syndrome.

Question 14

Describe Quad test

Answer 14

Done at 15-23 weeks. Based on pattern of AFP, hCG, uE3 and inhibin A; Designed to screen for Down syndrome, Trisomy 18 and ONTDs

Question 15

Describe first trimester test.

Answer 15

Done at 10-14 weeks. Detects PAPP-A and hCG. Tests for the amount of fluid at the back of the neck; Nuchal TranslucencyScreens for Down syndrome and trisomy 18. DOES NOT screen for ONTDs

Question 16

Describe the Full integrated test

Answer 16

Combines data from first and second trimesters; PAPP-A + NT + Quad

Question 17

Describe the Serum Integrated Test

Answer 17

Full integrated test without the NT; Lower detection rate and higher screen positive rate

Question 18

Describe the Ultrasound test

Answer 18

Performed at 20-22 weeks. Evaluates structure of fetus, amniotic fluid levels, and placenta; May detect ONTDs. Can’t diagnose or rule out any chromosomal anomaly. May detect soft signs(choroid plexus cysts, intracardiac echogenic foci)

Question 19

Describe Amniocentesis

Answer 19

Done at 15-23 weeks. Obtains amniotic fluid(Fetus cells); Measures amniotic AFP and acetylcholinesterase to screen for ONTDs

Question 20

Describe Chorionic Villi Sampling

Answer 20

Performed between 10-13 weeks; Analyzes chromosomes and DNA. Cant screen for ONTDs; May detect mosaicism (A second cell line present)

Question 21

Describe Preimplantation genetic diagnosis.

Answer 21

Utilized with IVF.

Question 22

Describe Non-Invasive Prenatal Screening.

Answer 22

Detects free fetal DNA and RNA in maternal blood; Detects Down Syndrome, Trisomy 18 & 13.