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OBGYN 1 > C7.0: 2nd and 3rd Trim. Biometry > Flashcards

C7.0: 2nd and 3rd Trim. Biometry Flashcards

1
Q

when is a nuchal lucency done? wks

A

11-14 wks

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2
Q

how do you measure the nuchal translucency?

A

inner to inner (echogenic area thru the hypo echoic fluid to echogenic skin)

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3
Q

what is a common mistake when measuring a nuchal lucency?

A

mistaking the amniotic membrane for the nuchal

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4
Q

do you zoom when doing a nuchal lucency?

A

yes

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5
Q

what does an increased nuchal lucency indicate?

A

chromosomal abnormalities
cardiac abnormalities
blood disorders
skeletal dysplasia

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6
Q

what nuchal lucency measurement is normal

A

~3mm

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7
Q

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

A 
BPD
occipital frontal diameter (OFD)
cephalic index (CI)
head circumference (AC)
abdominal circumference (AC)
femur length
fetal weight
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8
Q

when do you do a BPD?

A

starting at 12 wks until term

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9
Q

when would you use a BPD for dating of preg? how accurate was it?

A

in the 2nd trimester if dating wasn’t done in the 1st trimester
+/- 7 days in early 2nd trimester

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10
Q

what intracranial landmarks are used for the BPD measurement and where are they located in the brain?

A

falx cerebri (anterior and posterior)
thalami (middle)
cavum septi pellucidi (anteriorly)

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11
Q

how should the falx cerebri appear on the US screen?

A

create a flat line across the screen

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12
Q

How do you measure the BPD?

A

outer to inner edge of the skull bones across the widest part of the head

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13
Q

when demonstrating the CSP on US, how should it appear and why?

A

like a box, not an equal sign… showing the box rules out many fetal abnormalities

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14
Q

when imaging the CSP, what landmarks may you see anteriorly?

A

the anterior horns of the ventricles

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15
Q

which three head measurements are taken at the same level?

A

head circumference, BPD and occipital frontal diameter

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16
Q

should the HC be around the outside or inside of the skull?

A

outside

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17
Q

can the OFD and BPD be done at the same time?

A

yes

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18
Q

how do you measure the OFD?

A

from the outer margin of the frontal bone to the outer margin of the occipital bone.

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19
Q

the BPD and OFD are used to calculate what?

A

the cephalic index

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20
Q

how do you calculate cephalic index?

A

(BPD/OFD) X 100

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21
Q

what are the two things that head shape influences?

A

BPD and estimation of fetal age

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22
Q

whats the norm range for cephalic index?

A

75-85%

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23
Q

what is dolichocephaly and brachycephaly?

A

doli: narrow head
brachy: wide head

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24
Q

when is a fetus considered to have dolichocephaly and brachycephaly?

A

doli: <75%
brachy: >85%

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25
Q

what can cause dolichocephaly?

A

if the baby is breached or has low fluid

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26
Q

what 2 measurements can be used to calculate HC? and whats the formula?

A

BPD and OFD

HC= (BPD + OFD) X 1.57

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27
Q

how is the BPD measured for the HC calculation?

A

outer to outer, ONLY for this calculation

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28
Q

Is HC more or less dependent on shape than BPD?

A

less

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29
Q

whats the formula for Abdominal circumference and where are the callipers placed?

A

AC= (AP diameter of abdo + TRANS diameter of abdo) X 1.57

callipers are placed around the outer surface of the skin

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30
Q

for which measurements do we use an ellipse?

A

AC and HC

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31
Q

what are the landmarks for where you should take the AC?

A 
umbilical vein draining into portal vein (hockey stick)
stomach
adrenal glands
round shape
ribs
3 ossification centres of the spine
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32
Q

what does IUGR stand for?

A

intrauterine growth restriction

33
Q

whats the most important measurement to determine fetal growth?

A

AC

34
Q

how should you change your scanning window if youre on the fetal abdomen and you are showing the umbilical vein all the way to the skins surface?

A

you are too inferior on the anterior aspect of the abdomen

35
Q

how should you change your scanning window if youre on the fetal abdomen and you are showing the kidneys?

A

you are too inferior on the posterior aspect of the abdomen

36
Q

which structures should be seen when scanning the fetal abdomen? and which are less frequently seen?

A

live, kidney, GB, vasculature, bladder

spleen
pancreas

37
Q

list the head to abdomen ratios before 32 wks, from 32-36 wks and after 36 wks

A

before 32: head > abdomen

32-36 wks: head = abdomen

after 36 wks: head < abdomen

38
Q

when is femur length the most accurate?

A

between 14 and 22 weeks

39
Q

why is it important to measure the femur?

what is considered an abnormal femur?

A

assess for skeletal and chromosomal abnormalities

short for gestation age is abnormal

40
Q

which femur should you measure and what is the most optimal window to measure the femur?

which part of the femur do you measure?

A

the femur closest to the probe

make the femur perpendicular to the sound beam

only the diaphysis (blunt ends)

41
Q

how do you find the femur?

A

follow the abdomen down to the iliac bones, move the prove to the anterior aspect of the fetus… rotate until the femur is elongated

42
Q

when are the epiphysis seen?

A

after 32 weeks

43
Q

list the additional 2nd trimester measurements at are only done once @ the detailed scan

A 
cerebellum size
nuchal fold
cisterna magna size
ventricular size
binocular distance
all long bones
44
Q

what is the nuchal fold measurement? how and when do we do it?

A

thickness of the skin at the back of the neck
measure from outer occipital bone to outer skin surface

from 16-20 wks

45
Q

what is an abnormal nuchal fold and what % of fetuses with an abnormal measurement will have Down syndrome?

A

> or equal to 6mm is abnormal

45%

46
Q

how do you measure the cisterna magna and what is the upper limit of normal?

A

from edge of the cerebellum to inner occipital bone

upper of normal is 10mm

47
Q

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

A

> 90%

48
Q

how will the cerebellum and cistern mag appear with spinal bifida?

A

banana shaped…. and you wont see the cisterna magna

49
Q

why do we measure the ventricular atrium/trigone?

and where in the brain to we take this measurement compared to the BPD?

A

to assess for hydrocephalus (dilation of ventricles dur to blockage

slightly more cephalic than the BPD

50
Q

which ventricle do we measure and where?

A

ventricle furthest from the probe at the parietal occipital fissure

51
Q

whats the upper limit of normal for the trigone?

A

10mm

52
Q

what should the anterior horns measure at under 24 wks

A

<20mm

53
Q

what is the trigone/atria?

A

where the body, temporal horn and occipital horn meet

54
Q

How many ‘soft’ markers are concerning when doing a fetal assessment? why

A

2+

they increase the chances that baby has chromosomal abnormalities

55
Q

The yolk sac can often be seen on an EV ultrasound when the MSD is how many mm?

The embryo can often be seen on an EV ultrasound when the MSD measures how many mm?

A

8mm

16mm

56
Q

The yolk is readily visualized on a transabdominal ultrasound when the MSD measures how many mm?

The embryo is readily visualized on a transabdominal ultrasound when the MSD measures how many mm?

A

20mm

25mm

57
Q

when do you use MSD measurement?

A

4-8wks

58
Q

what is the mean sac diameter of the gest. sac for 6, 7 and 8 weeks?

how much does it grow every day?

A

6: 15 mm
7: 20 mm
8: 30 mm

(L+ W+D/3)

1.1 mm

59
Q

when is CRL used? wks

A

6-13wks

60
Q

when is oligohydraminios used? and how do we find it?

with what value is low fluid suspected?

A

5.5-9 wks

MSD-CRL…. if this value is <5mm

61
Q

when is the CSP seen on US?

A

18-27 wks

62
Q

if youre showing the equal sign instead of the box for the CSP whats the structure youre actually seeking?

A

columns of the fornix

63
Q

a normal CSP should be how many times longer than wide?

A

1.5x

64
Q

can the cerebellum measurement be used to determine gestation age? if yes, when?

A

yes

from 14-22 wks, the size in mm will correspond to gestational age

65
Q

what are the landmarks for where you should take the cerebellar measurement?

A

cavum septum pellucid and cerebellum with cisterna magna

66
Q

what plane do we use to image the orbits when measuring the orbital distance? how do we measure them?

does orbital distance change with gestation?

A

trans plane through the orbits and the skull.
measure outer to outer orbit

yes

67
Q

what is hypotelorism and hypertelorism?

A

hypo: eyes too close together
hyper: eyes to far apart

68
Q

which long bones do we always measure in the detailed scan?

when would you measure the others?

A

femur and humerus

only if they look abnormal… looking for skeletal dysplasia

69
Q

are clavicles considered a long bone?

A

yes

70
Q

why would we do a chest circumference?

A

sm chest is lethal because lungs cant develop properly

71
Q

are feet and hands effects by skeletal abnormalities?

A

no

72
Q

can you measure foot length for gestation age?

A

yes

73
Q

which two boney features can be an indication of Down syndrome?

A

polydactyl

and an absent or hypoplasic nasal bone

74
Q

b/w what growth percentile in a fetus considered normal?

A

10-90%

75
Q

whats considered large for GA?

what can it be caused by?

A

> 90%

caused by gestation diabetes or maternal obesity

76
Q

what happens in terms of fetal abdomonal growth if mom has GDM?

A

abdomen grows faster due to more exposure to glucose

77
Q

whats macrosomia? what are potential complications for baby?

A

weight >4000g

  • increased morbidity and mortality b/c they’re hard to deliver
  • baby can become hypoglycaemic post delivery
78
Q

whats considered SGA? what causes it?

what are potential complications for baby?

A

<10%
can be due to IUGR which can be caused by multiple pregancies, placental insufficiency, chromosomal abnormalities

increased morbidity and mortality

79
Q

compare symmetrical to asymmetrical IUGR

A

symmetrical:

  • all measurements are sm
  • commonly caused by choromosomal abnormalities
  • account for 25% of all IUGR
  • occurs in early 2nd trimester

asymmetrical:

  • head is norm size but abdomen is small
  • commonly caused by placental insufficiency
  • 75% of all IUGR
  • occurs in late 3rd trimester

OBGYN 1 (24 decks)

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