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Gynecology > 2nd & 3rd Trimester Biometry > Flashcards

2nd & 3rd Trimester Biometry Flashcards

1
Q

What are the 3 measurements that are taken in the first trimester?

A
  1. Mean sac diameter (MSD)
  2. Crown rump length (CRL)
  3. Nucheal lucency
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2
Q

When is the MSD used?

A

When the embryo is not identifiable

To compare embryo size to sac size

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3
Q

What do you have to ensure you see when measuring the MSD?

A

Double decidual sign

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4
Q

What weeks is this measurement used?

A

4-7 to 8 weeks

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5
Q

What is the formula for MSD?

A

Length + Width + Height / 3

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6
Q

What is the growth of the gestational sac daily?

A

1.1mm/day

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7
Q

What are the measurements for the YS and embryo on a EV scan?

A

YS- 8mm

Embryo- 16mm

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8
Q

What are the measurements for the YS and embryo on a TAS scan?

A

YS- 20mm

Embryo- 25mm

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9
Q

When is the CRL measurement used?

A

6-13 weeks

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10
Q

What is the most accurate measurement to predict gestational age?

A

CRL

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11
Q

How accurate is the CRL?

A

+/- 3 days

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12
Q

How do you measure the CRL?

A

Measure from tip of head to end of rump

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13
Q

Do you include the yolk sac in the CRL?

A

No

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14
Q

What position should the baby be lying in when obtaining the CRL?

A

Neutral position

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15
Q

When is early oligohydramnios measures?

A

5 1/2 - 9 weeks

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16
Q

What is the formula to calculate oligohydramnios?

A

MSD (mm) - CRL (mm)

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17
Q

When is the nuchal lucency test preformed?

A

Done b/w 11 and 14 weeks

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18
Q

When imaging for a nuchal test, do you take a longitudinal or short axis picture of the fetus?

A

Long axis

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19
Q

Do you magnify to see nuchal lucency?

A

Yes ++

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20
Q

What can you commonly mistake the nuchal lucency for?

A

Amnionic membrane

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21
Q

How do you measure the nuchal lucency?

A

On to on

Echogenic area thru hypo echoic fluid to echogenic skin

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22
Q

What are some indications of increased nuchal fluid? (5)

A
  1. Increased nuchal
  2. Chromosomal abnormalities
  3. Cardiac abnormalities
  4. Blood disorders
  5. Skeletal dysplasias
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23
Q

What are the routine measurements for the 2nd & 3rd semester? (7)

A
  1. BPD
  2. Occipital frontal diameter (OFD)
  3. Cephalic index (CI)
  4. Head circumference (HC)
  5. Abdominal circumference (AC)
  6. Femur length
  7. Femur weight
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24
Q

When trimester is the BPD the most accurate?

A

2nd

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25
Q

How accurate is the BPD within the early 2nd semester?

A

+/- 7 days

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26
Q

What are the intracranial landmarks for the BPD? (3)

A
  1. Falx cerebri (anterior and posterior)
  2. Thalami in the middle
  3. Cavum septi pellucidi anterior;y
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27
Q

How does the falx appear in the BPD measurement?

A

Should create a flat line across the screen

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28
Q

How should your markers be positioned for the BPD measurement?

A

Outer to outer

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29
Q

Label the image on pg 18..

A

See pg 18

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30
Q

What is the name of the additional ventricle positioned posterior to the cavum septi pellucidi?

A

Cavum Verge

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31
Q

What does the Cavum verge fill with?

A

Nothing- eventually closes

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32
Q

What part of the head do you measure for the BPD?

A

Widest section of head

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33
Q

What other measurement is taken at the same level/conjunction as the BPD?

A

Occipital frontal diameter (OFD)

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34
Q

What are the BPD and OFD used to calculate?

A

Cephalic Index

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35
Q

How should your markers be positioned for the OFD?

A

Outer margin of the frontal bone to the outer margin of the occipital bone

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36
Q

What influences the BPD estimation of fetal age?

A

Head shape

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37
Q

What is the formula used to calculate cephalic index?

A

CI = BPD/OFD X 100

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38
Q

What is the normal range for the cephalic index?

A

75-85%

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39
Q

What is the shape of a dolichocephalic head?

A

Narrowed head

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40
Q

What % of fetuses have a dolichocephalic head?

A

< 75%

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41
Q

What is the shape of a brachycephalic head?

A

Wide head

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42
Q

What % of fetuses have a brachycephalic head?

A

> 85%

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43
Q

What 2 calculations can be used to calculate the HC?

A

BPD and OFD

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44
Q

What is the formula for HC?

A

HC= (BPD+OFD) X 1.57

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45
Q

How is the BPD measured in reference to calculating the HC?

A

Outer to outer

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46
Q

Is the HC less or more dependent of the shape of the head then the BPD?

A

Less dependent

47
Q

What is the formula for the AC?

A

AC = AP diam + TRV diam X 1.57

48
Q

Where are the calipers placed when measuring the AC?

A

Around outer skin

49
Q

What are the AC landmarks? (6)

A
  1. Umbilical vein driving into portal sinus
  2. Stomach
  3. Round in shape
  4. Adrenal glands
  5. Ribs
  6. 3 ossification centres of the spine
50
Q

What is the “hockey stick sign”

A

Umbilical vein draining into the portal sinus

51
Q

Look at the planes through the abdomen on pg 33…

A

Refer to pg 33…

52
Q

What are the fetal abdominal structures easily identified?

A

Liver, kidneys, GB, vasculature and UB

53
Q

What abdominal structures are less frequently identified?

A

Spleen and pancreas

54
Q

What is the head to abdomen ratio BEFORE 32 weeks?

A

Head > abdomen

55
Q

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

A

Head = abdomen

56
Q

What is the head to abdomen ratio AFTER 32 weeks?

A

Head > abdomen

57
Q

When is the femur length most accurate?

A

B/w 14 and 22 weeks

58
Q

Why is it important to assess the femur?

A

To detect skeletal and chromosomal abnormalities

59
Q

What femur should you measure?

A

Measure the femur closest to the transducer

Make femur perpendicular to the sound beam

60
Q

Describe how you find the femur on the fetus

A
  • Follow the ado down to the iliac bones
  • Move the transducer to the anterior aspect of the fetus
  • Rotate transducer until femur is elongated
61
Q

What part of the femur do you measure?

A

Only the diaphysis

62
Q

Do you include the epiphysis?

A

No

63
Q

When is the epiphysis of the femur seen?

A

Not until 32 weeks

64
Q

What are the second trimester additional measurements? Do you have to include them if you have them from the detailed exam?

A 
Cerebellar size
Nuchal fold
Ventricular size
Binocular distance
All long bones

Don’t have to do these measurements if you have them from the detail scan

65
Q

What are the land marks used when measuring the cerebellum?

A

Cavum septi pellucidi and cerebellum with cistern magna

66
Q

Can the cerebellar measurement be used in deterring gestational age?

A

Yes

67
Q

When and how is the cerebellar used to measure gestational age?

A

From 14-22 weeks
The # of weeks in mm corresponds to the gestational age

EX: 15mm = 15 weeks

68
Q

When is the nuchal FOLD thickness measured?

A

16-20 weeks

69
Q

How do you measure the nuchal FOLD thickness?

A

Outer occipital to outer skin surface

70
Q

What is considered an abnormal value for the nuchal FOLD thickness?

A

> or = 6mm

71
Q

What % of fetuses with a thickened nuchal fold will have down syndrome?

A

45%

72
Q

Where do you put the calibers when measuring the cistern magna?

A

From the edge of the cerebellum to inner occipital bone

73
Q

What is the upper limit of normal when measuring the cistern magna?

A

1cm

74
Q

Seeing the cisterna magna rules out what % of the spinal defects and DWM?

A

> 90%

75
Q

What structure does the ventricular atrium (Trigone) use to assess?

A

Hydrocephalus

76
Q

At what level on the fetus is the trigone measured?

A

Slightly higher then the BPD

77
Q

Which vent of the trigone do you measure?

A

Vent farthest from the probe

78
Q

What is the upper limit of normal for the trigone?

A

1cm

79
Q

What is the trigone or atria?

A

Area where body, temporal horn and occipital horn meet

80
Q

When is the binocular distance (orbital) taken?

A

Detailed scan at 18 weeks

81
Q

Describe the biocular distance (orbital)

A

Transverse image through both orbits as well as the cranium

82
Q

Does the orbital distance change with gestational age?

A

Yes

83
Q

Where are the calibers placed when measuring the orbits?

A

Outer orbit to outer orbit

84
Q

What can the orbital distance inform use about the fetuses eyes?

A

Hypotelorism and hypertelorism

85
Q

What part of the fetuses eyes do you need to see to ensure their liable?

A

Lens

86
Q

Are both sides of the long bones scanned?

A

Yes

87
Q

Why are the long bones scanned?

A

To assess skeletal dysplasia

88
Q

What long bones are scanned first?

A

Femur and humerus

89
Q

If the femurs and humeri are abnormal what other bones do you scan?

A

Tibia, fibula, radius, ulna, clavicles and chest circumference

90
Q

Why is the foot length measured?

A

For gestational age

91
Q

Specifically why are the phalanges assessed?

A

For down syndrome

92
Q

What other bones are assessed and indicators for down syndrome?

A

Nasal bones

93
Q

Are the hands and feet affected by fibrous dysplasia?

A

No

94
Q

How is the biometry plotted on the graph to assess gestational age?

A

Plotted according to LMP

95
Q

What are 2 reasons to have an US to assess size?

A

LGA (large for gestational age) and SGA (small for gestational age)

96
Q

When is a fetus considered LGA?

A

> 90%

97
Q

Why can a fetus be LGA?

A

Maternal obesity, post dates or gestational diabetes

98
Q

How does gestational diabetes mellitus affect the fetus?

A

The abdomen grows at a increased rate bc of increased exposure to glucose

99
Q

What is macrosomia?

A

When the fetus weight is > 4000 grams

100
Q

Why do fetuses with macrosomia have increased morbidity and mortality rates?

A

Because they are difficult to deliver

101
Q

What can occur to a macrosomia fetus, whose mother has diabetic?

A

Fetus can become hypoglycemic

102
Q

When is the fetus considered SGA?

A

Biometry < 10%

103
Q

Why may SGA occur?

A

May due to intrauterine growth restriction (IUGR)

104
Q

What can cause IUGR? (8)

A 
Multiple pregnancies
Maternal hypertension
Placenta insufficiency
Vascular dx
Anemia, poor nutrition 
Smoking
Substance abuse
Chromosomal abnormalities
105
Q

What are fetuses with SGA at risk for?

A

Increased risk of fetal morbidity or mortality

106
Q

What is asymmetric IUGR?

A

Head normal but abdomen small

107
Q

What causes asymmetric IUGR?

A

Due to placenta insufficiency

108
Q

What % of cases incorporate asymmetric IUGR?

A

75%

109
Q

What semester does asymmetric IUGR present itself?

A

3rd trimester

110
Q

What is symmetric IUGR?

A

All measurements are small

111
Q

What causes symmetric IUGR?

A

Usually due to chromosomal abnormalities

112
Q

What % of cases incorporate symmetric IUGR?

A

25%

113
Q

What semester does symmetric IUGR present itself?

A

2nd trimester

Gynecology (4 decks)

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