Genetic screening in OBGYN

Question 1

what is the purpose of prenatal screening?

Answer 1

define the risk of a genetic disease in a low risk population

Question 2

what is the purpose of a screening test? what can they NOT do?

Answer 2

to assess the risk that a child will have a genetic disease; they cannot confirm or rule out the presence of the disease

Question 3

when is a diagnostic test given? what is the purpose?

Answer 3

given if a screening test is positive, to assess whether the disease is present or absent

Question 4

1st trimester screening tests test for what diseases? what are the markers?

Answer 4

• trisomies: 13, 18, 21

- markers: HCG, PAPP-A, nuchal translucency (NT)

Question 5

what is nuchal translucency? when is it seen?

Answer 5

measures the size of the fluid collection at the back of the fetal neck that can be seen 10-14 weeks gestation

Question 6

the serum markers + US yield what % detection rate?

Answer 6

82-87%

Question 7

what should you do if you find an increased risk of aneuploidy?

Answer 7

offer genetic counseling and diagnostic testing by CVS or amniocentesis

Question 8

what is the earliest that chorionic villus sampling can be done?

Answer 8

10 weeks

Question 9

when can amniocentesis be performed for genetic testing?

Answer 9

15-20 weeks

Question 10

when is percutaneous umbilical blood sampling performed?

Answer 10

usually after 20 weeks

Question 11

what are the US markers for aneuploidy?

Answer 11

• discovery of a structural malformation of a major fetal organ or structure OR
• the finding of two or more minor malformations increases the risk of aneuploidy sufficiently to warrant genetic testing of the fetus regardless of parental karyotype

Question 12

why do women aged 35 or over require amniocentesis?

Answer 12

risk of having fetus affected by aneuploidy is equal to the risk of the procedure

Question 13

what tests are used to confirm karyotype of screening test that was previously determined?

Answer 13

• chorionic villus sampling
• amniocentesis
• percutaneous umbilical blood sampling

Question 14

should women who have had 1st trimester screening for aneuploidy undergo 2nd trimester serum screening in the same pregnancy?

Answer 14

no

Question 15

during which weeks is second trimester screening done?

Answer 15

15-20 weeks

Question 16

what are the components of the second trimester quad screen?

Answer 16

• maternal serum AFP
• HCG
• unconjugated estriol
• inhibin A

Question 17

what is integrated screening? what are the advantages? disadvantages?

Answer 17

• results of both 1st and 2nd trimester screening and US can be combined to increase the ability to detect Down syndrome and to adjust a woman’s age-related risk

ADVANTAGES:

• highest sensitivity with lower false positive rate
• fewer invasive tests

DISADVANTAGE:
- long wait time for results; fewer options to terminate pregnancy

Question 18

what is the most important initial step in identifying women at high risk for hereditary cancers?

Answer 18

thorough family history

Question 19

what clues indicate high risk for genetic cancer?

Answer 19

• cancer in first degree relatives
• cancers occurring at young ages (under 50)
• cancers in multiple generations
• many cancers in one individual

Question 20

type A HNPCC carries an increased risk of developing what cancers?

Answer 20

• colorectal

- endometrial

Question 21

type B HNPCC carries an increased risk of developing what cancers?

Answer 21

• type A
• ovarian
• gastric
• pancreatic

Question 22

what is the inheritance of type B HNPCC?

Answer 22

autosomal dominant