2nd and 3rd Trimester: Biometry Flashcards
what is the most accurate measurement in the 2nd trimester for dating pregnancy
biparietal diameter (BPD)
what is the best measurement for dating pregnancy for all trimesters
CRL
BPD is accurate by _____ in 2nd trimester
+/- 7 days
BPD is a ______ plane of the head at the level of the ____
transverse axial
thalamus
3 intracranial landmarks of BPD (and what they look like on US)
falx cerebri: horiz line (ant to post)
thalami in middle of brain: paired hypoechoic heart-shaped structures on either side of 3rd ventricle
cavum septi pellucidi: anterior hypoechoic box
box: ____
=: ____
when trying to see CSP for BPD
cavum septi pellucidi (wanted)
columns of fornix (not wanted but good enough)
a normal CSP is ____ longer than wide
1.5x
BPD is measured perpendicular to ___
falx cerebri
calipers for BPD are placed from ____ to ____
outer bone edge
inner bone edge
(LE to LE)
HC is measured at same level as ____
BPD
HC is measured with an ____ caliper
ellipse
the ellipse for the HC should be placed how along the skull
tightly around outer skull not including skin
OFD stands for
occipital frontal diameter
OFD is measured indirectly as part of the ___ calc
HC
OFD is measured from ____ margin of frontal bone to ____ margin of occipital bone
outer
outer
CI stands for
cephalic index
CI = _________
(BPD/OFD)x100
CI is used to determine if the ___ can be considered accurate for determination of fetal age as head shape influences ____
BPD
BPD
normal range for CQ
75-85%
dolichocephalic = ______ (CI index/shape)
< 75% (narrow head)
brachycephalic = _____ (CI index/shape)
> 85% (wide head)
HC = _______ (formula for an ellipse)
(BPD + OFD) x1.57
the HC is ___ dependent on shape than the BPD
less
AC stands for
abdominal circumference
AC is taken at
transverse plane of fetal abdomen taken at the level of the fetal liver
AC landmarks (6) (one is just the shape)
stomach
umbilical vein draining into portal sinus
round shape
rib symmetry
adrenal glands (not kidneys)
spine (3 ossification centers)
AC calipers are placed around the _____
outer surface of the skin including fat and muscle
how many AC measurements do you have to take
at least 3
how to take AC if no ellipse on machine
two measurements (AP and TRX) taken at 90 degrees to each other
AC = _______ (formula)
(AP diameter + TRX diameter) x 1.57
fetal abdominal structures identified on US (5 main, 2 less frequently demonstrated)
liver
kidneys
gallbladder
vasculature
urinary bladder
less:
spleen
pancreas
before 32 weeks: head ___ abdomen
>
32-36 weeks: head ___ abdomen
=
after 36 weeks: head ___ abdomen
<
FL stands for
femur length
when does FL correlate well with GA
between 14-22 weeks
is the FL have the same GA accuracy as BPD and HC
no its less
FL measurement criteria for how to set up image/what is seen (3)
femur perpendicular to beam (0-15 degrees)
measure femur closest to transducer
both ends of bone clearly visible
callipers are placed at each end of bone, _____ the shaft. Only measure ____ not ____ (FL)
bisecting
diaphysis
epiphysis
when is the epiphysis seen on US
> 32 weeks gestation
3 steps to go from AC to FL
start AC, sweep towards fetal pelvis down to iliac bones
move transducer to ant aspect of fetus
rotate transducer until long axis of femur seen
2nd trimester measurements (7)
BPD
HC
AC
FL
HL
OFD
CI
2nd trimester measurements (6)
cerebellum size
nuchal fold
cisterna magna size
ventricular size
biocular distance
all long bones
when are 2nd semester additional measurements taken
18-20 weeks at detailed anatomy scan
cerebellum size: from __-__ weeks the diameter in mm corresponds to GA
14-22
2 landmarks for cerebellum size
trans-cerebellar plane
CSP anteriorly with cisterna magna posteriorly
cerebellum size is measured from
outer hyper edge to outer hyper edge
nuchal fold thickness is a measurement between the ______ and _______
occipital bone
outer skin surface
nuchal fold thickness measured from __-__ weeks
16-22
nuchal fold thickness is measured in the same plane as the _______
cerebellum
nuchal fold thickness is measured from _____ to _____
outer occipital bone
outer skin surface
it is sometimes helpful to angle the NF ______ slightly (not perfectly perpendicular)
anteriorly
Nuchal fold thickness: ____ is abnormal
≥6mm
____ of fetuses with trisomy 21 will have a thickened nuchal fold
80%
cisterna magna is a measurement of the ______ between the edge of the ____ to the _____
hypoechoic space
cerebellum
inner occipital bone
cisterna magna is measured in the same plane as the
cerebellum and nuchal fold
cisterna magna is measured from
inner to inner
cisterna magna upper limit of normal is
1cm/10mm
seeing the cisterna magna rules out ____ of spinal defects
> 90%
ventricular measurement is measured at the atrium of the ______. It is taken slightly more ____ than BPD
lateral ventricle (trigone)
cephalic
ventricular measurement is taken to asses for _____
hydrocephalus
trigone or atria is what
area where body, temporal horn, and occipital horn of lateral ventricles meet
landmarks for ventricular measurement (ant/post)
ant: cavum septi pellucidi
post: lateral ventricle with choroid plexus
measure ventricle _______ from transducer
farthest
measure ventricle at the level of the _________
parietal occipital fissure
ventricle is measured ______ to _____
inner
inner
ventricular measurement upper limit of normal
1cm/10mm
anterior horns of lateral ventricle should be ____ at <24weeks
<2cm
if you see a hanging choroid plexus that means that the ventricle is _____
dilated
biocular distance (orbital)
trans image through both orbits
biocular distance is measured from _____ orbit to _____ orbit
outer
outer
8 long bones measured
tibia
fibula
femur
radius
ulna
humerus
clavicles
chest circumference
foot length can be used for GA when:
Long bones are shortened
an absent or hypoplastic (small) nasal bone increases the chance of _______
chromosomal abnormalities
the US machine can configure an estimated fetal weight if all 4 of these biometry measurements are done:
BPD
HC
AC
FL
LGA stands for
large for gestational age
LGA is when biometry ____
> 90%
LGA is commonly due to (3)
gestational diabetes, maternal obesity, post dates
macrosomia is when the weight > ______
4000 grams
IUGR
intrauterine growth restriction
asymmetric IUGR vs Symmetric IUGR (sizes, usually due to, percentage of IUGR, occurs in what trimester)
asymmetric: normal head/small abdomen, usually due to placenta insufficiency, 75% of all IUGR, 3rd trimester
symmetric: all measurements small, usually chromosomal abnormality, 25%, 2nd trimester
3 planes of fetal biometry head
transventricular
transthalamic
transcerebellar
what is measured in transventricular plane
atria/trigone of lat vent
what is measured in the transthalmic plane
BPD/HC
what is measured in the transcerebellar plane
diameter of cerebellum, cisterna magna, and nuchal fold
what is the common landmark in all 3 planes (head) of these measurements
cavum septi pellucidi
cerebellum measured _____ to ___ and size in mm corresponds to ___
outer
outer
GA
cisterna magna measured ____ to ___ and up to ____ is normal
inner
inner
10mm
nuchal fold measured ___ to ____ and ___ is abnormal
bone
outer aspect of skin
≥6mm
AC is measured _____ to ____ and we take ___ measurements
outer
outer
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