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Obstetrics and Gynecology > 2nd and 3rd Trimester: Biometry > Flashcards

2nd and 3rd Trimester: Biometry Flashcards

1
Q

what is the most accurate measurement in the 2nd trimester for dating pregnancy

A

biparietal diameter (BPD)

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2
Q

what is the best measurement for dating pregnancy for all trimesters

A

CRL

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3
Q

BPD is accurate by _____ in 2nd trimester

A

+/- 7 days

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4
Q

BPD is a ______ plane of the head at the level of the ____

A

transverse axial
thalamus

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5
Q

3 intracranial landmarks of BPD (and what they look like on US)

A

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

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6
Q

box: ____
=: ____
when trying to see CSP for BPD

A

cavum septi pellucidi (wanted)
columns of fornix (not wanted but good enough)

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7
Q

a normal CSP is ____ longer than wide

A

1.5x

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8
Q

BPD is measured perpendicular to ___

A

falx cerebri

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9
Q

calipers for BPD are placed from ____ to ____

A

outer bone edge
inner bone edge

(LE to LE)

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10
Q

HC is measured at same level as ____

A

BPD

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11
Q

HC is measured with an ____ caliper

A

ellipse

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12
Q

the ellipse for the HC should be placed how along the skull

A

tightly around outer skull not including skin

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13
Q

OFD stands for

A

occipital frontal diameter

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14
Q

OFD is measured indirectly as part of the ___ calc

A

HC

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15
Q

OFD is measured from ____ margin of frontal bone to ____ margin of occipital bone

A

outer
outer

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16
Q

CI stands for

A

cephalic index

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17
Q

CI = _________ (formula)

A

(BPD/OFD)x100

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18
Q

CI is used to determine if the ___ can be considered accurate for determination of fetal age as head shape influences ____

A

BPD
BPD

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19
Q

normal range for CI

A

75-85%

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20
Q

dolichocephalic = ______ (CI index/shape)

A

< 75% (narrow head)

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21
Q

brachycephalic = _____ (CI index/shape)

A

> 85% (wide head)

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22
Q

HC = _______ (formula for an ellipse)

A

(BPD + OFD) x1.57

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23
Q

the HC is ___ dependent on shape than the BPD

A

less

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24
Q

AC stands for

A

abdominal circumference

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25
AC is taken at
transverse plane of fetal abdomen taken at the level of the fetal liver
26
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)
27
AC calipers are placed around the _____
outer surface of the skin including fat and muscle
28
how many AC measurements do you have to take
at least 3
29
how to take AC if no ellipse on machine
two measurements (AP and TRX) taken at 90 degrees to each other
30
AC = _______ (formula)
(AP diameter + TRX diameter) x 1.57
31
fetal abdominal structures identified on US (5 main, 2 less frequently demonstrated)
liver kidneys gallbladder vasculature urinary bladder less: spleen pancreas
32
before 32 weeks: head ___ abdomen
>
33
32-36 weeks: head ___ abdomen
=
34
after 36 weeks: head ___ abdomen
<
35
FL stands for
femur length
36
when does FL correlate well with GA
between 14-22 weeks
37
is the FL have the same GA accuracy as BPD and HC
no its less
38
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
39
callipers are placed at each end of bone, _____ the shaft. Only measure ____ not ____ (FL)
bisecting diaphysis epiphysis
40
when is the epiphysis seen on US
> 32 weeks gestation
41
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
42
2nd trimester measurements (7)
BPD HC AC FL HL OFD CI
43
2nd trimester additional measurements that are routinely taken(6)
cerebellum size nuchal fold cisterna magna size ventricular size biocular distance all long bones
44
when are 2nd semester additional measurements taken
18-20 weeks at detailed anatomy scan
45
cerebellum size: from __-__ weeks the diameter in mm corresponds to GA
14-22
46
2 landmarks for cerebellum size
trans-cerebellar plane CSP anteriorly with cisterna magna posteriorly
47
cerebellum size is measured from
outer hyper edge to outer hyper edge
48
nuchal fold thickness is a measurement between the ______ and _______
occipital bone outer skin surface
49
nuchal fold thickness measured from __-__ weeks
16-22
50
nuchal fold thickness is measured in the same plane as the _______
cerebellum
51
nuchal fold thickness is measured from _____ to _____
outer occipital bone outer skin surface
52
it is sometimes helpful to angle the NF ______ slightly (not perfectly perpendicular)
anteriorly
53
Nuchal fold thickness: ____ is abnormal
≥6mm
54
____ of fetuses with trisomy 21 will have a thickened nuchal fold
80%
55
cisterna magna is a measurement of the ______ between the edge of the ____ to the _____
hypoechoic space cerebellum inner occipital bone
56
cisterna magna is measured in the same plane as the
cerebellum and nuchal fold
57
cisterna magna is measured from
inner to inner
58
cisterna magna upper limit of normal is
1cm/10mm
59
seeing the cisterna magna rules out ____ of spinal defects
>90%
60
ventricular measurement is measured at the atrium of the ______. It is taken slightly more ____ than BPD
lateral ventricle (trigone) cephalic
61
ventricular measurement is taken to asses for _____
hydrocephalus
62
trigone or atria is what
area where body, temporal horn, and occipital horn of lateral ventricles meet
63
landmarks for ventricular measurement (ant/post)
ant: cavum septi pellucidi post: lateral ventricle with choroid plexus
64
measure ventricle _______ from transducer
farthest
65
measure ventricle at the level of the _________
parietal occipital fissure
66
ventricle is measured ______ to _____
inner inner
67
ventricular measurement upper limit of normal
1cm/10mm
68
anterior horns of lateral ventricle should be ____ at <24weeks
<2cm
69
if you see a hanging choroid plexus that means that the ventricle is _____
dilated
70
biocular distance (orbital)
trans image through both orbits
71
biocular distance is measured from _____ orbit to _____ orbit
outer outer
72
8 long bones measured
tibia fibula femur radius ulna humerus clavicles chest circumference
73
foot length can be used for GA when:
Long bones are shortened
74
an absent or hypoplastic (small) nasal bone increases the chance of _______
chromosomal abnormalities
75
the US machine can configure an estimated fetal weight if all 4 of these biometry measurements are done:
BPD HC AC FL
76
LGA stands for
large for gestational age
77
LGA is when biometry ____
>90%
78
LGA is commonly due to (3)
gestational diabetes, maternal obesity, post dates
79
macrosomia is when the weight > ______
4000 grams
80
IUGR
intrauterine growth restriction
81
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
82
3 planes of fetal biometry head
transventricular transthalamic transcerebellar
83
what is measured in transventricular plane
atria/trigone of lat vent
84
what is measured in the transthalmic plane
BPD/HC
85
what is measured in the transcerebellar plane
diameter of cerebellum, cisterna magna, and nuchal fold
86
what is the common landmark in all 3 planes (head) of these measurements
cavum septi pellucidi
87
cerebellum measured _____ to ___ and size in mm corresponds to ___
outer outer GA
88
cisterna magna measured ____ to ___ and up to ____ is normal
inner inner 10mm
89
nuchal fold measured ___ to ____ and ___ is abnormal
bone outer aspect of skin ≥6mm
90
AC is measured _____ to ____ and we take ___ measurements
outer outer 3

Obstetrics and Gynecology (14 decks)

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