CLT Practice Questions - Preconception
Care
A 26-year-old African-American G1P0 woman presents to your office at seven weeks
gestation with her husband, who is also African-American. The patient's brother has sickle
cell anemia, and has been hospitalized on numerous occasions with painful crises requiring
narcotic pain medication and blood transfusions. What are the odds that this couple will have
a child with sickle cell anemia, if the carrier rate for sickle cell disease in the African
American population is 1/10?
A. 1 in 15
B. 1 in 60
C. 1 in 100
D. 1 in 160
E. 1 in 400 - correct answer-Incorrect! Correct answer is B. Sickle cell anemia is an
autosomal recessive condition that occurs in 1/500 births in the African-American population.
The carrier state, or sickle-cell trait, is found in approximately 1/10 African-Americans. Since
the patient's brother is affected, both of their parents have to be carriers. Each time two
carrier parents for an autosomal recessive condition conceive there is a 1/4 chance of
having either an affected or an unaffected child and a 1/2 chance of having a child who is a
carrier. Since the patient is unaffected, she has a 1/3 chance of not being a carrier and a 2/3
chance of being a carrier. The patient's husband has a 1/10 chance of being a carrier (the
general population risk for African-Americans). Thus, the chance that this couple will have a
child with sickle cell anemia is: 2/3 X 1/10 X 1/4 = 1/60.
A 28-year-old G0 woman presents with her husband for preconception counseling. Her
family is Ashkenazi Jewish from Poland. Her husband is 30 years old and is also Jewish.
They seek information about preconception and prenatal screening. Carrier screening
should be performed for all of the following conditions except:
A. Fanconi anemia
B. Tay-Sachs disease
C. Beta thalassemia anemia
D. Cystic fibrosis
E. Niemann-Pick disease - correct answer-Correct! Fanconi anemia, Tay-Sachs disease,
Cystic Fibrosis, and Niemann-Pick disease are all autosomal recessive conditions that occur
at an increased incidence in Jews of Ashkenazi descent. The Beta thalassemia is seen
mainly in Mediterranean populations.
A 28-year-old G1P0 woman is at 15 weeks gestation. Her husband's cousin has moderate
mental retardation. The most common cause of inherited mental retardation in this patient's
child would be?
A. Undiagnosed phenylketonuria (PKU)
B. Neonatal hypothyroidism
C. Fragile X syndrome
, D. Down syndrome
E. Autism - correct answer-C
Correct! Fragile X syndrome is the most common form of inherited mental retardation. The
syndrome occurs in approximately 1 in 3,600 males and 1 in 4,000 to 6,000 females. Down
syndrome is genetic but the majority of cases are not inherited.
A 30-year old G2P1 woman is at 11 weeks gestation. She had a triple screen with her last
pregnancy and would like to have aneuploidy screening with the current pregnancy. Which of
the following screening tests will provide the highest detection rate for trisomy 21 for this
patient?
A. First trimester combined test
B. Triple screen
C. Quad screen
D. Sequential screen
E. Serum integrated screen - correct answer-Incorrect! Correct answer is D. All of the tests
screen for trisomy 21 and trisomy 18. Detection rates provided at a 5% false positive screen
rate.
• First trimester combined test: first trimester nuchal translucency, PAPP-A (pregnancy
associated plasma protein A) and Beta-hCG
- 85% Detection Rate
• Sequential screen: (first trimester NT and PAPP-A + second trimester quad screen)
- 93% Detection Rate
• Serum integrated screen, when unable to obtain nuchal translucency: (first trimester
PAPP-A + second trimester quad screen)
- 85-88% Detection Rate
A 30-year-old G0 woman presents with her husband for preconception counseling. The
patient is of Jewish Ashkenazi descent. Her husband is Irish. The patient has a brother who
has a child diagnosed with attention deficit hyperactivity disorder. Which of the following
genetic diseases is the most likely to affect their future children?
A. Canavan disease
B. Bloom syndrome
C. Cystic fibrosis
D. Tay-Sachs disease
E. Gaucher's disease - correct answer-C
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