Exam 3 - Genetic Testing

Question 1

What is the current trend in pregnancy that accounts for more genetic abnormalities?

Answer 1

Fewer births at ages 15-19, but more in women ages 30-44 years

• Higher chromosomal abnormalities and aneuploidy

Question 2

First trimester genetic screening methods

Answer 2

• Cell free DNA
• Nuchal translucency ultrasound
• Nasal bone calcification evaluation
• Chorionic villus sampling (CVS)

Question 3

What is cell free DNA testing?

Answer 3

Aka “non-invasive prenatal testing” (NIPT)

• Samples baby DNA in mother’s blood that is analyzed for evidence of extra or missing fetal DNA segments
• Can be done as early as 9-10 weeks
  
  • Detected at 10-22 weeks

Question 4

What are the pros and cons of cell free DNA genetic testing?

Answer 4

• Cons: cannot screen for neural tube defects
• Pros: can detect trisomies, sex chromosome abnormalities

Question 5

What is nuchal translucency ultrasound?

Answer 5

Performed at 10-14 weeks in conjunction with blood draw for free beta hCG and PAPP-a

• Looks for evidence of Down’s syndrome

Question 6

What is nasal bone calcification evaluation?

Answer 6

Improves detection of trisomy 21

Question 7

What is chorionic villus sampling (CVS)?

Answer 7

Small sample of cells are removed from placenta via abdomen or vagina

• Performed between 10-14 weeks

Question 8

Pros and cons of chorionic villus sampling (CVS)

Answer 8

• Pros: provides karyotype and definitive answer if screening tests are positive
• Cons: risk of fetal loss/miscarriage

Question 9

Second trimester genetic screening methods

Answer 9

• Quad screen
• 2nd trimester ultrasound
• Amniocentesis

Question 10

What is the quad screen?

Answer 10

Done at 15-18 weeks, up to 22 weeks, to detect neural tube defects (trisomy 18 and 21, abdominal wall defects)

• Includes hCG, maternal serum alpha fetoprotein (MSAFP), estriol, inhibin A

Question 11

Second trimester ultrasound markers for aneuploidy

Answer 11

• Short humerus or femur
• Pyelectasis
• Nuchal thickening
• Echogenic bowel or intracardiac focus

Question 12

What is amniocentesis?

Answer 12

Uses small needle to draw out amniotic fluid containing cells from the fetus

• Done between 15-22 weeks
• Can confirm CVS findings

Question 13

For which patients would amniocentesis be indicated?

Answer 13

• Advanced maternal age (>35 years)
• High risk pregnancy
• Positive genetic screen
• Abnormal ultrasound findings
• History of aneuploidy

Question 14

Pros and cons of amniocentesis

Answer 14

• Pros -
  
  • Most comprehensive of all genetic tests
  • Can detect neural tube defects
• Cons - invasive, carries risk of miscarriage