Module 17: Nuchal Translucency Flashcards
What view must the fetus be in for a NT?
Mid-sagittal
What six structures should be seen in a mid-sagittal view of the fetus?
- Midline structures of brain
- Mesencephalon
- Cerebellum
- 4th ventricle
- Cisterna magna
- Occipital bone
In a fetus with a chromosomal abnormality when does the nuchal fluid begin to increase and when does it decrease?
Increases at 11 weeks
Decreases after 14 weeks
What are factors that would cause an increased nuchal translucency?
- Chromosomal defect
What is the minimum CRL for NT?
45 mm (11weeks)
What is the maximum CRL for NT?
84 mm (13w6d)
Describe the necessary magnification for a NT: (2)
- Only fetal head and thorax on image
2. 3-4 cm depth on screen
What is nuchal translucency?
The U/S appearance/size of the subcutaneous accumulation of fluid behind the fetal neck in the 1st trimester of pregnancy
What is the window of time that nuchal translucency can be done?
11 wks - 13wk 6 days
What is NT inaccurate after 14 weeks?
Vertical fetal position changes NT
How accurate is NT on it’s own?
80%
How accurate is NT + blood work?
90%
What blood work is done with NT?
- bHCG
- PAPPA
What is 30 min lab processing time called?
OSCAR
One Stop Clinics for early Assessment of Fetal Risk
What is the necessary position for NT?
- True SAG (nasal bone + nuchal together)
- Fetus in neutral position
How can hyperextension affect the NT?
Can create a 0.6 mm increase in NT
Head turned can increase as well
How can flexion affect the NT?
Can create a 0.4mm decrease in NT
What is the criteria for the amnion when doing NT?
Fetus should be lifted off the amnion
Where should the NT measurement be done? (2)
- Widest portion of NT
- Anywhere from occiput to the thorax
What is the caliper placement for NT?
Inner to inner
What is the pregnancy loss rate of amniocentesis?
1/200
What is the mean NT for CRL of 45mm and 84mm?
45mm = mean NT of 1.2 mm
84mm = mean NT of 1.9 mm
What is the meas of NT in the 95 percentile for a CRL of 45mm and 84mm?
45mm = NT of 2.1mm
84 mm = NT of 2.7 mm
What is the 99 percentile (NT) for CRL of 45mm and 84mm?
Both = NT of 3.5 mm
1% of pregnancies
What is a nuchal umbilical cord?
A cord that is wrapped around the neck
How is NT measured in the presence of a nuchal umbilical cord?
The NT meas is taken above and below the cord and then averaged.
