Screening for fetal aneuploidy and ONTD's

Question 1

ONTD’s

Answer 1

Screening methods include:

1. Ultrasound- Done between 18 and 20 weeks. Detection rate is dependent on the institution.
2. MSAFP- Done between 15 and 20 weeks. Optimal time: 16-18 weeks. Detects 75-90% of all ONTD’s, 95+% of anencephaly and 85% of ventral wall defects.

Diagnostic test:
1. Amniocentesis: Amniotic fluid AFP and Acetylcholinesterase

Question 2

Factors that affect maternal serum screening results

Answer 2

• Appropriate dating
• twin v. singleton (presence of twins increases cut-off’s 2x)
• Race
• IDDM (diabetes)
• Family history
• Maternal weight

Question 3

Diagnostic tests for fetal aneuploidy

Answer 3

Detection rate is virtually 100% (dates based on ACMG guidelines, not Magee or West Penn’s protocol)

• CVS- can be done between 10w and 13w
• Amniocentesis- can be done at 15 weeks

Question 4

What is the time cut-off for a discrepancy in gestational age after an U/S that a test result needs to be reinterpreted?

Answer 4

> 10 days

Question 5

What does first trimester screening measure?

Answer 5

• Pregnancy-associated plasma protein A (PAPP-A)
• Human chorionic gonadotropin (hCG)
• Nuchal translucency (NT) measurement

Question 6

When is blood drawn for first trimester screening?

Answer 6

Between 9 weeks and 13 weeks 6 days gestation

Crown rump length 24 - 84 mm

Question 7

What first trimester screening markers are indicative of trisomy 21?

Answer 7

• Reduced PAPP-A levels
• Increased hCG levels
• Increases NT measurement

Question 8

What first trimester screening markers are indicative of trisomy 18?

Answer 8

• Reduced hCG levels

- Increased NT measurement

Question 9

What chromosome conditions does first trimester screening look for?

Answer 9

• Down Syndrome

- Trisomy 18

Question 10

What is the nuchal translucency (NT)?

Answer 10

• Fluid filled or sonolucent space behind the fetal neck

Question 11

What are increased NT measurements associated with?

Answer 11

• Down Syndrome
• Other aneuploidies
• Congenital heart defects
• Diaphragmatic hernias
• Skeletal dysplasias
• Variety of genetic syndromes

Question 12

ACOG recommends that patients with a fetal NT measurement of 3.5 mm or higher should be offered what?

Answer 12

• Targeted U/S

- Echocardiogram

Question 13

Second Trimester Screening (when is it performed and what does it screen for) - also referred to as “quad screen”

Answer 13

• Performed at 15 - 20 weeks

- Screens for trisomies 21 and 18 as well as open neural tube defects (ONTDs)

Question 14

What are the biochemical markers that second trimester screening uses

Answer 14

• Alphafetoprotein (AFP)
• hCG
• unconjugated estriol (uE3)
• dimeric inhibin-A

Question 15

What is the cutoff risk for Down Syndrome for second trimester screening?

Answer 15

1 in 270

Question 16

Detection rates of second trimester screening for Down Syndrome

Answer 16

• Detects ~75% of the cases of Down Syndrome cases for women under 35
• 80% of the cases of Down Syndrome in women 35+

Question 17

What is indicative of Down Syndrome in second trimester screening?

Answer 17

• Reduced levels of AFP and uE3

- Increased levels of hCG and dimeric inhibin-A

Question 18

What is the “triple test”

Answer 18

• Part of second trimester screening
• AFP, hCG, and uE3 are considered the “triple test”
• Has a sensitivity of ~65% for Down Syndrome and 70% for trisomy 18

Question 19

What is indicative of trisomy 18 in second trimester screening?

Answer 19

• Reduced levels of AFP, hCG, and uE3

Question 20

ACMG recommends that all women should have the option of ___________

Answer 20

• Invasive diagnostic testing for fetal aneuploidy by CVS or amniocentesis
• Screening for aneuploidy and ONTD’s for those that present for prenatal care before 20 weeks gestation

Question 21

Women who undergo first trimester screening and/or CVS should be offered __________

Answer 21

MSAFP screening and/or an ultrasound for the detection of neural tube defects between 15 and 20 weeks gestation