Second and Third Trimester- Basic Scan Flashcards
The second trimester is what weeks?
13-27 (3-6 months)
Between what weeks can performing an ultrasound allow you to image all organs and predict due date?
16-26 weeks GA
The spine can be identified sonographically by which week?
16-18 weeks
The spine is completely ossified by?
Week 18
The 3 ossification centers can be seen by?
16 wks GA
What are the 3 ossification centers?
2 posterior (laminae) and 1 and anterior (centrum)
The 3 ossification centers are best seen in which plane?
Transverse
The central portion of the spine appears how sonographically?
hypoechoic
The lumbosacral spine is not completely ossified until?
> 18 wks GA
Where can the lateral ventricles be seen?
on either side of the midline falx
The midline falx is also called?
interhemispheric fissure
The lateral ventricles should not exceed?
10 mm
How do you measure the lateral ventricles?
inner to inner through the atrium
True or False: Both the normal anterior and posterior horns of the lateral ventricles are seen sonographically
False; only posterior horns
Where is hydrocephalus first seen?
lateral ventricles (dilated lateral ventricles or ventriculomegaly)
Where is the choroid plexus located?
in the lateral ventricles
How does the choroid plexus appear sonographically?
echogenic
What is the function of the choroid plexus?
produce CSF
By when is the brain anatomy visualized?
12-14 wks GA
Where can the thalami be visualized?
on either side of the midline
What serves as the landmark for the BPD and HC?
thalami, CSP, midline falx
What is the thin echogenic line seen between the thalami?
third ventricle
Where can the cisterna magna be visualized?
in the posterior fossa posterior to cerebellum
The cisterna magna should never exceed?
10 mm
Where is the cerebellum located?
in the posterior fossa
How does the cerebellum appear sonographically?
two hypoechoic lobes with an echogenic vermis seen between
An absent vermis can cause?
splaying of cerebellum
What is the cavum septum pellucidum (CSP)?
slit like space that is midline separating the anterior horns of lateral ventricles
How does the CSP appear sonographically?
anechoic rectangle in anterior part of the head
Circulation of CSF
- CSF produced by choroid plexus
- Flows through Foramen of Monro to 3rd ventricle (between thalamus)
- Aqueduct of Sylvius connects 3rd and 4th ventricle
- CSF flows through subarachnoid space through the Foramen of Luschka and Foramen of Magendie
- CSF is absorbed into dural venous sinuses via arachnoid villi
The nuchal thickness (nuchal fold) should not exceed?
< 5-6 mm
How does CSF appear sonographically?
anechoic
By when is the 4 chamber heart identified sonographically?
16-18 wks
The apex of the heart should point where?
left side of fetus
Which portion of the heart is closest to the chest wall?
right ventricle
Which portion of the heart is closest to the spine?
Left atrium
The fetal heart should occupy ______ of the chest.
1/3
Where is the tricuspid valve located?
between the right atrium and right ventricle
Where is the mitral/bicuspid valve located?
between left atrium and left ventricle
The foramen ovale shunts blood from?
the right atrium to the left atrium
The foramen ovale turns into what when it closes?
fossa ovalis
Which portion contains more oxygenated blood?
left atrium
What is the normal fetal heart rate?
120-160 bpm
A fetal heart rate of < 100 bpm indicates?
bradycardia
A fetal heart rate of >180 bpm indicates?
tachycardia
Which ventricle has thicker walls? why?
left; higher forces needed to pump blood through body
The fetal stomach is identified sonographically by?
Wk 10; better seen by wk 14 due to improvement of fetal swallowing
How does the stomach appear sonographically?
round, fluid filled structure on left side of fetal abdomen
What are the landmarks for AC?
stomach, portal vein, spine
The gallbladder is identified sonographically at?
20 wks GA
Where is the gallbladder located?
right of midline
The fetal adrenal glands have a _______ adrenal cortex and a ______ medulla.
hypoechoic; echogenic
The fetal kidneys start producing urine when?
13-15 wks
what structure in the heart can be confused for a fetal anomaly?
chordae tendineae
What is a major component of amniotic fluid?
fetal urine (16-18 wks GA)
By when are the kidneys more visible?
3rd trimester
How do the renal pelves appear sonographically?
anechoic slit within central kidney
How do the renal pelves appear sonographically?
anechoic slit within central kidney
The renal pelves should not exceed?
6 mm
What vessels does the umbilical cord consist of?
2 umbilical arteries and 1 umbilical vein (3 vessel cord)
The 3 vessels of the umbilical cord creates what sonographically?
mickey mouse sign
True or false: Some umbilical cords can have 1 umbilical artery and 1 umbilical vein
True (2 vessel cord); normal varient
What kind of blood do the umbilical arteries carry?
deoxygenated
The umbilical arteries arise from which vessels?
hypogastric arteries
The umbilical vein carries what kind of blood?
oxygenated
The umbilical vessels are encased by?
wharton’s jelly
True or False: you should image the umbilical cord with color doppler
False; can cover defects
What is a nuchal cord?
umbilical cord encircles fetal neck
By when is the bladder identified sonographically?
10 wks
The fetal bladder fills every ______.
30 minutes
What can be indicated by a failure to image the bladder?
UTI
True or False: A UTI can be life threatening to a fetus
true
What is the measurement for GA in the third trimester?
Femur length
How do you measure the femur length?
measure the diaphysis
What is the lateral bone of the lower arm? Medial bone?
radius; ulna
What is the lateral bone of the lower leg? Medial bone?
fibula; tibia
True or False: Hands and feet are required for basic guidelines
False; not required
True or False: BPD and HC are measured on the same plane
True
Where should the fetal head measurements be taken?
at the level of the thalamus and CSP in the axial plane
What are the most accurate measurements of the second trimester?
BPD and HC
How is the BPD measured?
from outer edge of partietal bone to inner edge of parietal bone (leading edge to leading edge)
How is the HC measured?
outer to outer
What is OFD?
Occipito-frontal diameter
When do you use OFD?
when head shape is questionable (not oval)
Mesocephalic
normal shape (70-86% CI)
Dolicocephalic
long and narrow (<70% CI)
Brachycephalic
broad and round (>86% CI)
Brachycephalic
broad and round (>86% CI)
Which head shape is associated with Down Syndrome?
Brachycephalic
What is the CI?
cephalic index
The AC is measured at what level?
level of stomach and junction of umbilical vein and left branch of portal vein
True or False: The AC measurement includes fetal skin
True
True or False: the kidneys and adrenal glands are not included in AC
true
In the second trimester, what can signify the gender is a boy?
turtle sign
In the second trimester, what can signify the gender is a girl?
hamburger sign
Amniotic fluid is 98% ______
water
What is the function of amniotic fluid?
protects fetus, regulates body temperature, allows for movement, aids in development of muscles and skeletal structures
What is amniotic fluid critical for?
fetal lung development
What is the AFI
amniotic fluid index
How do you measure AFI?
divide the uterine cavity into 4 quadrants and measure the deepest pocket of each quadrant then add all 4 measurements
What is the normal range of the AFI measurement?
> 8 and <24 cm
What is SDP?
single deepest pocket
How do you measure SDP?
find the deepest pocket of fluid
What is the normal range for the SDP?
> 2 and < 8 cm
Define polyhydramnios and it’s measurements for AFI and SDP
too much amniotic fluid; AFI: > 24 cm; SDP: > 8 cm
True or false: polyhydramnios provides good resolution
True
Define oligohydramnios and it’s measurements for AFI and SDP
not enough amniotic fluid; AFI: < 8cm; SDP: < 2 cm
True or false: oligohydramnios provides good resolution
false; poor resolution
SDP is also called?
MVP (maximal vertical pocket)
What is vernix and how does it appear sonographically
normal desquamated skin cells, she’d hair, and sebum; echogenic particles in amniotic fluid
What is meconium and how does it appear sonographically?
menacing sign of bowel contents in amniotic fluid; grey and hazy
What is the formula for CI?
BPD/OFD x100
