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DMST 244 Obstetrics and Gyn Sonography 1 > Module 7: 2nd And 3rd Trimester Biometry > Flashcards

Module 7: 2nd And 3rd Trimester Biometry Flashcards

1
Q

For 2nd and 3rd trimester measurements what are the routine measurements? 7

A
  1. Biparietal diameter (BPD)
  2. Head circumference (HC)
  3. Abdominal circumference (AC)
  4. Femur length (FL)
  5. Humerus Length (HL)
  6. Occipital frontal diameter (OFD)
  7. Cephalic index (CI)
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2
Q

How accurate is Biparietal diameter compared to other 2nd trimester dating?

A

The most accurate measurement in the 2nd trimester for dating a pregnancy

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3
Q

Can we use Biparietal diameter measurements in the 1st trimester?

A

Yes

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4
Q

When can we use the Biparietal diameter (BPD)?

A

+/- 7 days on early 2nd trimester

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5
Q

What are some BPD landmarks? 3

A
  1. Falx cerebri
  2. Thalami in the middle of the brain
  3. Cavun septi pellucidi
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6
Q

The BPD land marks are what kind?

A

Intracranial landmarks

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7
Q

What is the Falx cerebri? 2

A
  1. Fibrous structure that separates the cerebral hemispheres
  2. Visualized as a horizontal line - anterior to posterior
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8
Q

What is the thalami in the middle of the brain?

A

Paired hypoechoic structures that appear heart- shaped and lie on either side of the 3rd ventricle

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9
Q

What kind of landmark is the Cavum septi pellucidi? What does it look like?

A
  1. Anterior landmark in the brain.
  2. Hypechoic box
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10
Q

What is the blue box?

A

Cavum Septi Pellucidi

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11
Q

What do we need to remember about getting the CSP?

A

Make sure that we don’t get the box not the equal signs.

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12
Q

What is the BPD measurement criteria? 4

A
  1. Perpendicular to Falx (as possible)
  2. Symmetric hemispheres
  3. Measure at the widest point across the skull
  4. Calibres placed from outer bone edge to inner bone edge on the opposite side
    leading edge to leading edge
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13
Q

What does leading edge to leading edge look like?

A
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14
Q

Label the structures

A
  1. Anterior horn of lateral ventricle
  2. 3rd ventricle
  3. Anterior occipital horn with choroid plexus (closest to transducer)
  4. Posterior occipital horn with choroid plexus (farthest from
    transducer)
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15
Q

What are some BPD pitfalls? 3

A
  1. Head not perpendicular
  2. Cerebellum
  3. CSP not well seen
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16
Q

Label the structures

A
  1. The Falx is the structure that separates the straight line
  2. The CSP is the box
  3. The Thalami is the farthest left box
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17
Q

Where is the Head circumference (HC) measurement taken? What kind of caliper is used? How should we use it?

A
  1. Measured at the same level as the BPD
  2. Measured with an ellipse calliper
  3. Eclipse should be placed tightly around the outer skull (do not include skin)
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18
Q

What kind of landmarks are we looking for in terms of the Head Circumference?

A

Same landmarks as BPD

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19
Q

Occipital frontal diameter (OFD) can be done in conjunction with what?

A

BPD

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20
Q

OFC is obtained at what level?

A

Same level as BPD

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21
Q

How should measure OFD?

A

Measure from outer margin of the frontal bone to the outer marginal of the occipital bone

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22
Q

BPD and OFD are used to calculate what?

A

Cephalic index (CI)

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23
Q

What is the formula for Cephalic index (CI)?

A

CI = (BPD/OFD)(100)

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24
Q

What is the normal range for Cephalic index?

A

75% to 85%
The BPD is considered accurate for determining fetal age if the Cephalic index falls within range

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25
Q

What is two types of Cephalic index?

A
  1. Dolichocephalic
  2. Brachiocephalic
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26
Q

What is a dolichocephalic head?

A

<75% (narrow head)

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27
Q

What is a brachycephalic head?

A

> 85% (wide head)

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28
Q

Label the two Cephalic index heads from left to right

A

Left: Brachycephalic
Right: Dolichocephalic

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29
Q

What are Brachycephalic do to the Gestational age?

A

Overestimates it

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30
Q

What does the Dolichocephalic do for the Gestational Age?

A

It underestimates it

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31
Q

What does the brachycephalic measure do in terms of BPD?

A

It renders the BPD less accurate

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32
Q

What does the dolichocephalic do in terms of the BPD?

A

It renders the BPD less accurate

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33
Q

How do we calculate head circumference?

A

BPD and OFD are used to calculate head circumference.

HC = (BPD + OFD) x 1.57

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34
Q

How do we calculate Head circumference on the machine?

A

The machine does it automatically, they will have a ellipse calliper to measure head circumference

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35
Q

How much more is HC dependant on shape compared to BPD?

A

Less dependent on shape than the BPD

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36
Q

What is the abdominal circumference level?

A

Transverse plan of the fetal abdomen at the level of the fetal

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37
Q

What are some landmarks we look for with AC? What kind of shape should the AC look like? What should the ribs look like? 5

A
  1. Stomach
  2. Umbilical vein draining into portal sinus
  3. Round shape
  4. Rib Symmetry
  5. Adrenal glands (not kidneys)
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38
Q

What is this?

A

The Abdominal circumference

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39
Q

What are the AC measurement Criteria? 3

A
  1. Calliper are placed around the outer surface of the skin
  2. Includes fat, skin, and muscle
  3. Machines use an ellipse for the AC measurement
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40
Q

How many measurements do we need for the AC measurement method

A

At least three measurements

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41
Q

What is the formula for AC?

A

AC = AP diameter + TRX diameter x 1.57

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42
Q

With AC, how would the Umbilical vein be visualized? Which level would we measure AC? How would the kidneys be visulized?

A
  1. Umbilical vein would be visualized anteriorly
  2. Is a good AC
  3. Kidneys would be visualized posterior on this image
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43
Q

Label the structures

A
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44
Q

What are fetal abdominal structures identified on US? 5

A
  1. Liver
  2. Kidney
  3. Gallbladder
  4. Vasculature
  5. Urinary bladder
45
Q

What are some less frequently demonstrated abdominal structures? 2

A
  1. Spleen
  2. Pancreas
46
Q

The head and abdomen grow at what rates?

A

Different rates

47
Q

What is the size difference on the head and abdomen before 32 weeks?

A

Head > abdomen

48
Q

What is the head to abdomen ratio between 32 - 36 weeks?

A

Head = Abdomen

49
Q

What is the head to abdomen ratio after 36 weeks?

A

Head < abdomen

50
Q

Femur length correlates well with what and when? Why?

A

Gestational age between 14 and 22 weeks (less accurate later in pregnancy)

51
Q

In terms of accuracy how does Femur length compare to BPD and HC?

A

Not as accurate

52
Q

Why is it important to get femur length? 3

A

To look for
1. Skeletal abnormalities
2. Chromosomal abnormalities
3. Short for gestational age is abnormal

53
Q

What are Femur length measurement criteria? 3

A
  1. Femur must be perpendicular to sound beam
  2. Measure femur closest to the transducer
  3. Both ends of bone clearly visible
54
Q

Where should we place the calliper for femur length?

A

Callipers should be placed at each end bisecting the shaft

55
Q

When measuring the femur if it looks bent what should we do?

A

Use a different window

56
Q

Where on the femur should we measure?

A

The diaphysis (shift) do not include epiphysis

57
Q

When are 2nd trimester additional measurements done?

A

18-20
Routinely performed at the detailed anatomy scan

58
Q

What are additional things that we measure during the 2nd trimester? 6 (Besides biometry)

A
  1. Cerebellum size
  2. Nuchal fold
  3. Cisterns magna size
  4. Ventricular size
  5. Binocular distance
  6. All long bones
59
Q

Cerebellum size correlates with what?

A

Gestational age

60
Q

What is the range of the diameter for cerebella’s measurement?

A

14 to 22 is the diameter in mm that corresponds to the gestational age

61
Q

What plane is the cerebella taken? What is a landmark of the cerebella’s measurements?

A
  1. Trans- cerebellielar
  2. Cavum septi Pellucidi (CSP)
62
Q

What are some criteria for Cerebeullar measurements? How should we measure it?

A
  1. Balanced, symmetrical cerebellum
  2. Measures from other echogenic edge to ethogenc edge
63
Q

What is nuchal folds

A

Measurement of the space between the occipital bone and outer skin surface

64
Q

When is the measurement of the Nuuchal fold thickness done?

A

Measured from 16 - 20 weeks

65
Q

What plane is Nichal fold measured as?

A

Same plane as cerebellum

66
Q

What is the range size of the nuchal fold thickness?

A

> 6mm is abnormal

67
Q

What percentage of fetus with Down syndrome will have a thickened nuchal fold

A

45%

68
Q

What is the cisterns magna?

A

Measurement of the hypoechoic space between the edge of the cerebellum to the inner occipital bone

69
Q

What plane is Cisterna Maga taken at?

A

In some plane as cerebellum and nuchal fold

70
Q

What is a landmarks of the transcerebellar plane?

A

Cavum septi Pellcida

71
Q

What is the criteria for cisterna magna measurements?

A

Measure Measure from edge of cerebellum to inner occipital bone
inner to inner

72
Q

What is the upper limit of normal for a cisterna magna measurement?

A

1cm or 10 mm

73
Q

Does Cisterna Magna change with gestational age?

A

Nope!

74
Q

Seeing the Cisterna magna rules out what?

A

90% of spinal defects

75
Q

Where are ventricular measurements done?

A

They are measured at the atrium of the lateral ventricle (trigone)

76
Q

What plane is ventricular measured at?

A

Slightly more Cephalic than BPD

77
Q

Why do we take ventricular measurements?

A

Assess for hydrocephalus

78
Q

What plane is ventricular measurements taken at? What is a landmarks for ventricular measurements? 2

A
  1. Trans-ventricular plane
  2. Cavum Septo Pellucidi
79
Q

What are some criteria for the ventricular measurements? 2

A
  1. Measure ventricle farthest from the transducer
  2. Measure at the level of the parietal occipital fissure
80
Q

What landmark is ventricular measurement done?

A

Parietal occipital fissure

81
Q

What is the upper limit of normal of parietal occipital fissue?

A

1cm or 10 mm

82
Q

Does ventricular measurement change with GA?

A

No

83
Q

What is binocular distance (orbital)?

A

Transverse image through both orbits as well as the Brancusi

84
Q

How should we measure for occipital?

A

Outer orbit to outer orbit

85
Q

What does biocular distance detect?

A

Hypotelorism and hyperteloriusm

86
Q

For binocular distance, the normal distance changes with what?

A

Gestational age

87
Q

What do we do in cases where FL or HL are measuring small?

A

Other long bones can also be measured

88
Q

Why do we measure long bones?

A

Assess for skeletal dysplasia or aneuoloidy

89
Q

What are some other skeletal measures we take? 2

A
  1. Foot length
  2. Nasal length
90
Q

Can foot length be used for gestational age?

A

Yes when long bones are shortened

91
Q

For gestational size compared to dates, the biometry is plotted on a graph to do what?

A

Assess gestational size for gestational age

92
Q

The biometry is plotted according to the estimated gestational age by what?

A

LMP or an early ultrasound

93
Q

Measuring small or large for dates are reasons to have what?

A

an ultrasound assess the fetal size

94
Q

The ultrasound machine can configure an estimated fetal weight if what4 things are done?

A

4 biometry measures are done
1. BPD
2. HC
3. AC
4. FL

95
Q

What is considered large for gestational age?

A

Biometry > 90%

96
Q

What would classified as large for gestational age?

A

Biometry > 90%

97
Q

What is a common reason for a biometry to large?

A

Gestational diabetes

98
Q

What is macrosomia?

A

Weight > 4000 grams

99
Q

Macrosomias have increased morbidity and mortality because of what? 2

A
  1. They have difficulties in delivery
  2. The newborn can become hypoglycaemic post delivery if mom had uncontrolled GDM
100
Q

What is considered small for gestational age?

A

Biometry < 10%

101
Q

What is IUGR?

A

Intrauterine growth restriction

102
Q

Symmetric IUGR vs Asymmetric IUGR: what is the basic difference ?

A

Asymmetric vs symmetric

103
Q

Symmetric IUGR vs Asymmetric IUGR: body measurements?

A

Head normal size but abdomen small vs All measurements are small

104
Q

Symmetric IUGR vs Asymmetric IUGR: abnormalities due to what?

A

Placenta insufficiency vs chromosomal abnormalities

105
Q

Symmetric IUGR vs Asymmetric IUGR: frequency

A

75% vs 25%

106
Q

Symmetric IUGR vs Asymmetric IUGR: trimester occurrence rate?

A

Occurs in 3rd trimester vs occurs in 2nd trimester

107
Q

Symmetric IUGR vs Asymmetric IUGR: occurrence rate?

A

Occurs in 3rd trimester vs occurs in 2nd trimester

108
Q

Symmetric IUGR vs Asymmetric IUGR: occurrence rate?

A

Occurs in 3rd trimester vs occurs in 2nd trimester

DMST 244 Obstetrics and Gyn Sonography 1 (22 decks)

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