Prenatal Genetics For Boards

Front 1

What is the timing for CVS?

What is the risk for earlier CVS?

Back 1

10-13+ weeks of gestation

Earlier: limb reduction defects when performed before 10 weeks

Front 2

What is the timing for amniocentesis?

What is the risk with earlier amnio?
What is the risk with later amnio?

Back 2

15-20 weeks gestation

Earlier: membranes must be fused, must have enough fluid, risk of clubfeet
Later: risk of premature birth

Front 3

What is the timing for the first-trimester blood draw?

Back 3

10-13.6 weeks

Front 4

What analytes are used in first-trimester screening?

What conditions do they test for?

Back 4

PAPP-A, hCG

Down syndrome, trisomy 18

Front 5

Down syndrome pattern of analytes in first trimester screening?

Back 5

High hCG, low PAPP-A

Front 6

Trisomy 18 pattern of analytes in first trimester screening?

Back 6

Low hCG, low PAPP-A

Front 7

What is the timing for the second-trimester blood draw?

Back 7

15-20 weeks

Front 8

What analytes are used in second-trimester screening?

What conditions do they test for?

Back 8

hCG, UE3, AFP, Inhibin

Down syndrome, trisomy 18, Smith-Lemli-Opitz, Neural tube defects/Abdominal wall defects

Front 9

Down syndrome pattern of analytes in second trimester screening?

Back 9

High hCG, low UE3, high inhibit, low AFP

Front 10

What might lead to a false positive Down syndrome result int he second trimester?

Back 10

Incorrect dating (fetus is younger than stated)

Front 11

SLOS pattern of analytes in second trimester screening?

Back 11

Low hCG, very low UE3, low AFP

Front 12

What is the timing for an NT ultrasound?

Back 12

11.2 weeks to 14.2 weeks

Front 13

If a CVS is performed what other screening is necessary?

Back 13

*Second trimester analytes for neural tube and abdominal wall defects.
*Ultrasound

Front 14

What conditions are associated with a large NT?

Back 14

*Aneuploidies: Down syndrome, Turner syndrome, trisomy 18, trisomy 13
*Noonan syndrome
*Nuchal defects: cystic hygroma, neck lipoma
*CNS defects, facial defects, cardiac defects, pulmonary defects, GI defects, genitourinary defects, skeletal defects, fetal anemia, neuromuscular defects, metabolic defects

Front 15

What is detected by amniocentesis?

Back 15

*99% of chromosome abnormalities
*Neural tube defects/abdominal wall defects (via AFP)

Front 16

What is the miscarriage risk for amniocentesis?

Back 16

<1/300 - 1/500

Front 17

What is the miscarriage risk for CVS?

Back 17

<1/300

Front 18

What is the chance for mosaicism with CVS?

Back 18

1-2%

Front 19

What is the detection rate for CVS?

Back 19

>99% for chromosome abnormalities

Front 20

What types of cells are taken in a CVS?

Back 20

Chorionic villi

Two culture types:
-Direct: middle layer (cytotrophoblast) is quickly dividing
-Indirect: remainder of sample (including outer syncytiotrophoblast and inner mesenchymal core)

Front 21

What ultrasound anomalies would necessitate a level 2 ultrasound?

Back 21

*Choroid plexus cysts
*Echogenic bowel
*Echogenic intracardiac focus
*Single umbilical artery
*Dilated renal pelvis
*Mild ventriculomegaly

Front 22

What is the general population risk for Down syndrome?

Back 22

1/800

Front 23

What is the general population risk for neural tube defects?

Back 23

1/1000

Front 24

What is the general population risk for congenital heart defect?

Back 24

1/100

Front 25

What is the general population risk for birth defect or mental retardation?

Back 25

3-4%

Front 26

What injection might be necessary during CVS or amniocentesis?

Back 26

Rhogam to avoid Rh sensitization

Front 27

What are the features of single umbilical artery?

Back 27

Usually, one vein (bringing oxygen and nutrients to baby), two arteries (bringing fetal waste to the maternal kidneys)

Front 28

What is the frequency of single umbilical artery?

Back 28

1/100

Front 29

Name the five risk factors for single umbilical artery

Back 29

Caucasian, female fetus, mother >40y, diabetes, multiple gestation

Front 30

What are the birth defects more common in fetuses with single umbilical artery?

Back 30

*Heart defects
*Kidney defects
*Vertebral (spine) defects
*Possible: slow fetal growth, preterm delivery, stillbirth

Front 31

What should be offered with the finding of single umbilical artery?

Back 31

Level 2 ultrasound, amniocentesis if other findings are present, 3rd trimester ultrasound for growth

Front 32

What is an echogenic bowel?

Back 32

A bright spot on the ultrasound due to the presence of dense material

Front 33

What is the frequency of echogenic bowel?

Back 33

<1/50

Front 34

What are the possible reasons for echogenic bowel?

Back 34

*Chromosome abnormalities (1/30)
*Cystic fibrosis (1/30)
*Fetal infection
*Intestinal blockage/atresia
*Poor fetal growth
*Other: reduced intestinal movement, swallowing blood from amniotic fluid, low maternal belly fat

Front 35

What fetal infections can cause echogenic bowel?

Back 35

TORCH (especially CMV). If mother is shown to be infected with CMV the fetus can be tested by amniocentesis.

Rubella, varicella, herpes, toxoplasmosis, and parvovirus also have been reported.

Front 36

What is a choroid plexus cyst?

Back 36

*Fluid collection in the spongy gland(s) that make cerebrospinal fluid.
*Can be unilateral or bilateral.
*Usually resolve by 24-36 weeks.
*Does not damage the brain.

Front 37

What is the frequency of choroid plexus cyst?

Back 37

1-2% of all second trimester fetuses

Front 38

What are the possible reasons for choroid plexus cyst?

Back 38

<1% risk for trisomy 18

Front 39

What is the measurement needed to diagnose dilated renal pelvis (pelviectasis, pyelectasis, hydronephrosis)?

Back 39

Mildly dilated: 5-9 mm
Hydronephrosis: >10 mm

Front 40

What is dilated renal pelvis?

Back 40

Back-up of urine into the renal pelvis

Front 41

What is the frequency of dilated renal pelvis?

Back 41

2-3% of pregnancies

Front 42

What are the potential causes of dilated renal pelvis?

Back 42

*Normal variation
*Obstruction of the ureter (ureteropelvic junction obstruction is the most common)
*Reflux of urine (usually due to a faulty bladder valve)

Front 43

What conditions are associated with dilated renal pelvis?

Back 43

*Male fetus
*Familial kidney disease
*Down syndrome (more likely if bilateral)

Front 44

What is the follow-up for dilated renal pelvis?

Back 44

*Level 2 ultrasound
*Amniocentesis if there are other findings
*32 week ultrasound for renal check
*After birth: renal ultrasound, urinalysis

Front 45

Is intervention in the pregnancy necessary for dilated renal pelvis?

Back 45

Not with normal amniotic fluid levels.

Front 46

Is intervention needed after birth for dilated renal pelvis?

Back 46

Rarely, no intervention if the dilation improves or remains stable

Front 47

What three factors can you use to estimate risk for chromosome anomaly?

Back 47

Mother's age, blood analytes, ultrasound markers

Front 48

Which ventricles are enlarged in ventriculomegaly? How large must they be?

Back 48

Lateral ventricles
Mild: 10-15 mm

Front 49

What is the other name for severe ventriculomegaly?

Back 49

Hydrocephalus

Front 50

What is the frequency of mild ventriculomegaly?

Back 50

1/1000

Front 51

What are the potential explanations for mild ventriculomegaly?

Back 51

*Normal variation
*Changes in cerebrospinal fluid flow
*Changes in brain development

Front 52

What conditions are associated with mild ventriculomegaly?

Back 52

*Physical birth defects (heart, kidney, spine)
*Chromosome abnormalities (1/25)
*Prenatal infection (CMV, toxoplasmosis- interfere with brain development)
*Genetic syndromes
*Brain development defects

Front 53

What is the follow-up for mild ventriculomegaly?

Back 53

*Level 2 ultrasound
*Amniocentesis for chromosome count and infection

Front 54

How often does mild ventriculomegaly progress?

Back 54

1/10

Front 55

What size of ventriculomegaly becomes a risk factor for learning disabilities/MR?

Back 55

12 mm

Front 56

Which screened analytes increase during the pregnancy?

Back 56

AFP, UE3

Front 57

Which screened analytes decrease during the pregnancy?

Back 57

hCG

Front 58

Which screened analytes do not change levels during the pregnancy?

Back 58

Inhibin

Front 59

What is the prenatal folic acid dose? With prior NTD?

Back 59

400 mcg; 4 mg

Front 60

Gravida _ / Para _ _ _ _

Back 60

Gravida: # of pregnancies
Para: term, preterm, abortion/miscarriage, living

Front 61

What prenatal age is considered preterm?

Back 61

24-37 weeks

Front 62

Which timeframe and measurement is the most accurate for ultrasound dating?

Back 62

Early first trimester; crown-rump length

Front 63

What is the frequency of monozygotic twins?

Back 63

1/300

Front 64

What is chorionicity?

Back 64

The placentation of embryos

Front 65

What are the pregnancy membranes and their location? How does this impact twin naming?

Back 65

*Amnion: first layer around baby
Chorion: second layer, attached to uterus
*You can be monochorionic and diamnionic but not dichrorionic and mono amnionic

Front 66

What is the rule of thumb for chronicity vs. zygosity?

Back 66

"Mono is always mono, but di is not always di"
(monochorionic twins are always monozygotic, but dichorionic twins are not always dizygotic)

Front 67

What is the "twin peak sign"? What does this indicate?

Back 67

A thick membrane separating the sacs, indicates di/di

Front 68

Which women do ACOG recommend offering options?

Back 68

Everyone

Front 69

When is the "all or none" period of pregnancy?

Back 69

Before implantation. First two weeks of embryonic development (from fertilization to implantation)= first 4 weeks of pregnancy

Front 70

When do the fetal organs develop? Which ones?

Back 70

3-8 weeks (heart, CNS, limbs, lips, teeth, palate, external genitalia)