Prenatal Screening Flashcards
What is the goal of a screening test?
To identify individuals with an unrecognized disease. To sort out those who probably have the disease from others who dont.
What is a critical value/cut-off?
A chosen value at which everyone at or above are considered ‘Screen Positive’
What happens if someone is Screen Positive?
Individuals are offered diagnostic testing to determine if they have the condition.
What is the test sensitivity?
The test’s ability to correctly identify those with the disease.
What is the test specificity?
The test’s ability to correctly identify those without the disease
What is the relationship between sensitivity and specificity?
They are in an inverse relationship to each other; You want a balance between the two.
What if there was a test that was 100% sensitive?
All affected individuals would be detected; Will have more false positives.
What if there was a test that was 100% specific?
All unaffected individuals will be identified; Will have more false negatives.
What is the relationship between maternal age and aneuploidy?
If the mother is older than 35, there is an increased risk for aneuploidy.
Give example of ethnicity based screening.
Minorities are screened for sickle cell and thalassemias; Ashkenazi Jewish are tested for Tay Sachs, CF, Canavan disease and Familial Dysautonmia.
What if someone tests negative in a carrier screening test?
A negative carrier test result reduces the risk of the condition but does not eliminate it.
What are the tests done only during pregnancy?
Done at 15-23. AFP, Quad, First Trimester, Full integrated, Sequential, Serum Integrated.
Describe AFP test
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.
Describe Quad test
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
Describe first trimester test.
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
Describe the Full integrated test
Combines data from first and second trimesters; PAPP-A + NT + Quad
Describe the Serum Integrated Test
Full integrated test without the NT; Lower detection rate and higher screen positive rate
Describe the Ultrasound test
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)
Describe Amniocentesis
Done at 15-23 weeks. Obtains amniotic fluid(Fetus cells); Measures amniotic AFP and acetylcholinesterase to screen for ONTDs
Describe Chorionic Villi Sampling
Performed between 10-13 weeks; Analyzes chromosomes and DNA. Cant screen for ONTDs; May detect mosaicism (A second cell line present)
Describe Preimplantation genetic diagnosis.
Utilized with IVF.
Describe Non-Invasive Prenatal Screening.
Detects free fetal DNA and RNA in maternal blood; Detects Down Syndrome, Trisomy 18 & 13.
