••• Chapter 16^ First Trimester Ultrasound^177
❍ What are the requirements for a good NT image?
- CRL between 45 and 84 mm.
- Fetus in midsagittal plane in neutral position.
- Distinguish between fetal skin and amnion.
- Magnified so fetus occupies 75% of the screen.
- Place calipers on inner margins of skin to soft tissue.
❍ What structure is the arrow pointing to in the ultrasound image?
Amnion.❍ Is TVUS required for NT measurement?
No. Often abdominal ultrasound is successful in 80% of cases.
❍ How does neck flexion and extension affect the NT?
Neck flexion decreases the NT by about 0.4 mm, while hyperextension increases the NT by about 0.6 mm.
❍ What first trimester biochemical analytes, along with NT, constitute an effective screening strategy for
aneuploidy?
PAPP-A (pregnancy-associated plasma protein A) and hCG (free or totalhCG).
❍ In pregnancies affected with Down syndrome, the hCG will be , and the PAPP-A will be __. NT
will be increased.
Increased, decreased.
❍ In pregnancies affected with Trisomy 18, the hCG will be , and the PAPP-A will be . NT will be
increased.
Decreased, decreased.