Module 7 : 2nd and 3rd Trimester Biometery Flashcards Preview

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Flashcards in Module 7 : 2nd and 3rd Trimester Biometery Deck (52)
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1

1st trimester measurements

- mean sac diameter (MSD)
- crown rump length (CRL)
- nuchal lucency

2

mean sac diameter

- used when embryo is not identified
- ensure you see the double decidual sign
- used from 4-7 or 8 weeks
- length+width+height/3

3

crown rump length

- used between 6-13 weeks
- most accurate measurement to predict gestational age =/- 3 days
- tip of head to end of rump
- in a neutral position

4

oligohydramnios measurement

- 5 1/2 - 9 weeks
- MDS(mm) - CRL(mm)
< 5mm = early oligo

5

nuchal lucency

- done between 11-14 weeks to rule out chromosomal abnormalities
- magnify to see nuchal lucency well
- DO NOT MISTAKE AMNIOTIC MEMBRANE FOR NUCHAL LUCENCY
- measure on to on

6

indications for nuchal lucency

- increased nuchal
- chromosomal abnormalities
- cardiac abnormalitites
- blood disorders
- skeletal dysplasia

7

upper limit of normal for nuchal

- 3 mm is upper limit of normal

8

2nd and 3rd trimester measurements

- Biparietal diameter (BPD)
- head circumference (HC)
- abdominal circumference (AC)
- femur length
- femur weight

9

biparietal diameter BPD

- most accurate measurement in the 2nd trimester for dating of pregnancy
- +/- 7 days in early 2nd trimester
- falx should create a line flat across the screen

10

inter cranial landmarks for BPD

- falx cerebri
+ anterior and posteriorly demonstrated in the brain
- thalami in the middle of the brain
- caved septum pellucidi anteriorly landmark in the brain

11

calliper placement for BPD

- leading edge to leading edge

12

where to measure BPD

- at the widest part across the head
- outer skull to inner skull

13

normal cavum septum pellicidum CSP

- 1.5x longer than wider

14

head circumference (HC)

- BPD only measured outer edge to outer edge in this calc only
- along the falx
- don't do BPD on same picture
- BPD and OFD can be used to calculate head circumference
- all machines have ellipse
- HC less dependant on shape than BPD

15

occipital frontal diameter (OFD)

- can be done in conjunction with the BPD
- taken at same level as BPD
- measure from OUTER margin of frontal bone to OUTER margin of occipital bone
- BPD and OFD used to calculate CEPHALIC INDEX

16

cephalic index

- head shape influences BPD estimation of of fetal age

17

cephalic index equation

CI = BPD / OFD x 100

18

normal cephalic index range

75% - 85%

19

dolichocephalic range

< 75%
- narrow head

20

brachycephalic range

> 85%
- wide head

21

head circumference equation

HC = (BPD + OFD) x 1.57

22

abdominal circumference

- callipers placed around outer surface of skin

23

abdominal circumference equation

AC = AP diameter = TRV diameter x 1.57

24

AC landmarks

- umbilical vein draining into portal sinus
- stomach
- adrenal veins
- round in shape
- ribs
- 3 ossification centres of spine

25

fetal abdominal structures identified on US

- liver
- kidneys
- gallbladder
- vasculature
- urinary bladder
- sometimes spleen , pancreas

26

head to abdomen ratios before 32 weeks

- head > abdomen

27

head to abdomen ratios 32-36 weeks

- head = abdomen

28

head to abdomen ratios after 36 weeks

- head < abdomen

29

femur length FL

- most accurate between 14-22 weeks
- important measurement to assess for skeletal abnormalities
+ short for gestational age is abnormal

30

how to measure femur length

- measure femur closest to the transducer
- make femur perpendicular to sound beam