Prenatal dx

Question 1

How to estimate gestational age in:

First trimester

Answer 1

Crown-rump length
(only useful in 1st trimester - cat curling up)
first trimester: 7 days

Question 2

How to estimate gestational age in:
2nd+3rd
(beyond 12 weeks)

Answer 2

1. Biparietal Diameter (BPD)
2. Abdominal circumference (AC)
3. Femur length (FL)

Question 3

What is AFP?

Where is it made?

Answer 3

What: fetal albumin

Made: fetal liver

Question 4

What do high +low levels of aFP mean?

Answer 4

High: 
1. Most is NOT a NTD (mom has incorrect dating, and shes further along than expected)
or 
2. Maternal-fetal hemorrhage
3.  Multiple gestations
4. NTD:  
Spina bifida, omphalocoele

Low: Down syndrome

Question 5

% of reported chromosomal abnormalities

Answer 5

1. Trisomy 21 (half)
2. Other
3. Trisomy 18

> 35 is considered advanced maternal age

Question 6

Complications of DS

Answer 6

1. Mental retardation
2. Growth retardation
3. Early alzheimers
4. Congenital heart defects
5. Hearing loss
6. Ophthalmic disorders

Question 7

hCG lvls elevated or low indicates?

Answer 7

Nl: NTD

High: Trisomy 21

Low:
Trisomy 18

Question 8

Increased lvls of inhibin A indicates?

Answer 8

Trisomy 21

Question 9

Low PAPP-A indicates?

Answer 9

Trisomy 13, 18, 21

Question 10

Nuchal translucency testing indicates:

- what week is it measured at?

Answer 10

90% accurate for detecting Trisomy 21

98% accurate for detecting trisomy 18

• Nuchal translucency

Question 11

Chorionic villus sampling
 detects:
Samples \_\_\_:
Completed at \_\_\_ weeks:
Can it detect NTD?
How is it beneficial to other sampling techniques?

Answer 11

Detects: genetic, metabolic, & DNA abnormalities

Samples developing placenta

Completed at 10-12 weeks

Can it detect NTD? No!

Earlier than amniocentesis

Question 12

Non invasive test with no miscarriage risk

Answer 12

Cell free fetal DNA testing

- available early in gestation

Question 13

Does massively parallel sequencing differentiate fetal vs maternal DNA?

Answer 13

NO!

But, Over-representation of chromosome 21 fragments in affected preg is significant.

Question 14

Population based approach

- example

Answer 14

Screening for NTD or Down Syndrome

Question 15

Specific population subgroups

- example

Answer 15

Thalassemia

Question 16

Highly targeted screening example

Answer 16

Families known to be carriers of certain diseases/genes

• hemophilia
• cardiac defects

Question 17

Cornerstones of prenatal dx

Answer 17

1. Personal hx
2. Family hx
3. Non directive counseling
4. Testing

Question 18

Examples of Noninvasive tests

Answer 18

Blood draw
(Maternal serum analytes: look for markers)

Ultrasound

Question 19

Invasive testing

• Examples
• Benefits and risk

Answer 19

Amniocentesis

Chorionic villus sampling (CVS)

• both:
• pose small risk to fetus
• Access to fetal cells: analyze chromosomal anomalies and single gene disorders

Question 20

Indications for invasive dx diagnosis includes: (5)

Answer 20

1. Advanced maternal age (>35 at due date)
2. Positive aneuploidy screening test
3. Abnl ultrasound finding
   - anatomic
   - IUGR
   - amniotic fluid volume
4. Known parental chromosome rearrangements
5. Previous affected child

Question 21

When is nuchal translucency measured?

Answer 21

10-14 weeks gest., when fetal lymphatic system is developing and the placental resistance is high.
- after 14 weeks, the lymphatic system can drain excess fluid, and peripheral resistance of placenta falls.
(abnl fluid accumulation can go undetected)

Question 22

What weeks can you evaluate internal organs and extremities for anatomic abnormalities at how many weeks gestation?

Answer 22

16-20 weeks gest.

• biparietal diam
• femur length
• abdom circ.

Question 23

When can amniocentesis be performed?

When can CVS be performed?

Answer 23

AC: With ultrasound guidance btwn 14-20 weeks gest.

CVS: 9.5-12.5 weeks