Trisomy 21

Question 1

What are the phenotypic features of trisomy 21?

Answer 1

-Flattened face -Outside corners of eyes are pointed upward -Small ears -Short neck -Narrow high arch palate -Single crease across the palms -Sandal gap feet

Question 2

What are soft markers for Trisomy 21 on ultrasound?

Answer 2

-Thickened nuchal translucency -Absent nasal bone -Tet with AVSD -Short limbs -Duodenal atresia -Single umbilical artery -Fetal pyelectasis -Club feet -Sandal gap

Question 3

Which soft marker carries the highest likelihood ratio for trisomy 21?

Answer 3

Nuchal translucency and fold

Question 4

How do you counsel a patient at 12 weeks with confirmed fetal trisomy 21?

Answer 4

-Expectant management verses pregnancy termination -Increased risk of pregnancy loss -Increased risk of anomalies -Varying degree of intellectual ability -Leukemia

Question 5

How do you counsel a patient at 12 weeks with confirmed fetal trisomy 21 and hydrops

Answer 5

Prognosis is grave, 90% risk of fetal death. Offer termination of pregnancy.

Question 6

What is the likelihood of spontaneous abortion for a fetus with trisomy 21 and hydrops?

Answer 6

High

Question 7

What percentage of first trimester spontaneous abortions are related to trisomy 21?

Answer 7

12%

Question 8

What percentage of fetuses with cystic hygroma in the first trimester will be diagnosed with trisomy 21?

Answer 8

37%

Question 9

If fetal trisomy 21 is suspected, how do you counsel the patient regarding additional testing options?

Answer 9

CVS verses amniocentesis depending on gestational age. Discuss risk of pregnancy loss, infection, bleeding, rupture of membrane and lack of amniocytes to culture

Question 10

How accurate is cell free DNA screening in the detection of fetal trisomy 21?

Answer 10

Detection rate is 99%

Question 11

What are possible explanations for cell free DNA results indicating high risk for trisomy 21?

Answer 11

-Maternal contamination -Mosaic placenta -Aneuploid placenta -Aneuploid fetus -Fals positive -Resorbed twin -Maternal malignancy

Question 12

What are the most common anomalies in a fetus with trisomy 21?

Answer 12

Nuchal transluncency Tet with AVSD Short limbs Single umbilical artery Duodenal atresia

Question 13

Can a microarray detect trisomy 21?

Answer 13

Yes it can detect copy number variants

Question 14

What advantage does a fetal karyotype have over microarray in a fetus with trisomy 21?

Answer 14

Can detect triploidy or balanced translocation

Question 15

How do you follow a patient during pregnancy with fetal trisomy 21?

Answer 15

Detailed anatomic survey Fetal echocardiogram Fetal growth Antenatal testing at 32 weeks with abnormal growth

Question 16

How do you counsel a patient regarding recurrence risks for trisomy 21?

Answer 16

It depends: Non-inherited extra chromosome -> 1% recurrence Translocated Down syndrome -> 50% recurrence

Question 17

What is the detection rate for T21 with NT alone?

Answer 17

70%

Question 18

What is the sensitivity of absent nasal bone in detecting T21?

Answer 18

49%

Question 19

What is the sensitivity of reverse ductus venosus wave form in detecting T21?

Answer 19

67%

Question 20

Duodenal atresia on ultrasound:

Answer 20

• Double bubble sign
• Polyhydramnios