OnlineMedEd: Obstetrics - "Prenatal Eval"

Question 1

How accurate is ultrasound in determining gestational age by trimester?

Answer 1

• 1st trimester: +/- 1 wk
• 2nd trimester: +/- 2 wks
• 3rd trimester: +/- 3 wks

Question 2

When are transcranial ultrasounds done to evaluate for fetal anemia?

Answer 2

After 20 weeks

Question 3

How should you interpret transcranial dopplers?

Answer 3

They’re highly sensitive, so if the TCD is normal then the fetus likely does not have anemia. If it’s positive, then the fetus might have it.

Question 4

Amniocentesis can be done to evaluate for ______________.

Answer 4

• Down syndrome (because you catch fetal cells in the fluid)
• Fetal lung maturity (lecithin:sphingomyelin ratio)

Question 5

What is the risk of fetal loss in amniocentesis?

Answer 5

1/300

Question 6

What advantages does CVS have over amniocentesis?

Answer 6

• It can be done earlier (10 wks)

* It has a lower chance of fetal demise (1/500)

Question 7

What is PUBS?

Answer 7

Percutaneous Umbilical Blood Sampling

Question 8

Why is PUBS not commonly used?

Answer 8

It can only be done closer to delivery, and if the fetus truly has anemia (discovered on TCD) then the proper course is to deliver.