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Ob/Gyne > Module 7 : 2nd and 3rd Trimester Biometery > Flashcards

Module 7 : 2nd and 3rd Trimester Biometery Flashcards

1
Q

1st trimester measurements

A
  • mean sac diameter (MSD)
  • crown rump length (CRL)
  • nuchal lucency
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2
Q

mean sac diameter

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

crown rump length

A
  • 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
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4
Q

oligohydramnios measurement

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

nuchal lucency

A
  • 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
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6
Q

indications for nuchal lucency

A
  • increased nuchal
  • chromosomal abnormalities
  • cardiac abnormalitites
  • blood disorders
  • skeletal dysplasia
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7
Q

upper limit of normal for nuchal

A
  • 3 mm is upper limit of normal
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8
Q

2nd and 3rd trimester measurements

A
  • Biparietal diameter (BPD)
  • head circumference (HC)
  • abdominal circumference (AC)
  • femur length
  • femur weight
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9
Q

biparietal diameter BPD

A
  • 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
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10
Q

inter cranial landmarks for BPD

A
  • falx cerebri
    + anterior and posteriorly demonstrated in the brain
  • thalami in the middle of the brain
  • caved septum pellucidi anteriorly landmark in the brain
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11
Q

calliper placement for BPD

A
  • leading edge to leading edge
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12
Q

where to measure BPD

A
  • at the widest part across the head

- outer skull to inner skull

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13
Q

normal cavum septum pellicidum CSP

A
  • 1.5x longer than wider
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14
Q

head circumference (HC)

A
  • 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
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15
Q

occipital frontal diameter (OFD)

A
  • 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
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16
Q

cephalic index

A
  • head shape influences BPD estimation of of fetal age
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17
Q

cephalic index equation

A

CI = BPD / OFD x 100

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18
Q

normal cephalic index range

A

75% - 85%

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19
Q

dolichocephalic range

A

< 75%

- narrow head

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20
Q

brachycephalic range

A

> 85%

- wide head

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21
Q

head circumference equation

A

HC = (BPD + OFD) x 1.57

22
Q

abdominal circumference

A
  • callipers placed around outer surface of skin
23
Q

abdominal circumference equation

A

AC = AP diameter = TRV diameter x 1.57

24
Q

AC landmarks

A
  • umbilical vein draining into portal sinus
  • stomach
  • adrenal veins
  • round in shape
  • ribs
  • 3 ossification centres of spine
25
Q

fetal abdominal structures identified on US

A
  • liver
  • kidneys
  • gallbladder
  • vasculature
  • urinary bladder
  • sometimes spleen , pancreas
26
Q

head to abdomen ratios before 32 weeks

A
  • head > abdomen
27
Q

head to abdomen ratios 32-36 weeks

A
  • head = abdomen
28
Q

head to abdomen ratios after 36 weeks

A
  • head < abdomen
29
Q

femur length FL

A
  • most accurate between 14-22 weeks
  • important measurement to assess for skeletal abnormalities
    + short for gestational age is abnormal
30
Q

how to measure femur length

A
  • measure femur closest to the transducer

- make femur perpendicular to sound beam

31
Q

finding femur

A
  • follow abdomen down to iliac bones
  • move transducer to the anterior aspect of fetus
  • rotate transducer until femur is elongated
32
Q

where to measure femur length

A
  • only measure diaphysis (shaft)
  • do not include epiphysis
    + not seen until > 32 weeks
33
Q

2nd trimester additional measurements

A
  • cerebellum size
  • nuchal fold
  • cisterna magna
  • ventricular size
  • binocular distance
  • all long bones
  • only done once at detailed scan
34
Q

cerebellar measurement

A
  • landmarks = caves septum pellucidi and cerebellum with cisterna magna
  • can be used for gestational age
  • from 14-22 the # in mm corresponds to gestational age
35
Q

nuchal fold thickness

A
  • 16-20 weeks
  • measure from outer occipital bone to outer skin surface
  • > /= 6mm abnormal
  • 45% of Down syndrome will have thickened nuchal fold
36
Q

cisterna magna

A
  • measure from edge of cerebellum to inner occipital bone
  • upper limit of normal is 1cm or 10mm
  • seeing cisterna magna rules out >90% of spinal defects in DWM
    + spina bifida
37
Q

ventricular atrium (trigone)

A
  • to assess for hydrocephalus (ventricles dilated because of CSF)
  • taken slightly more cephalic than BPD
  • measure ventricle farthest from the transducer
  • measure at the parietal occipital fissure
38
Q

upper limit of normal for ventricular trigone

A
  • 1cm - 10mm
39
Q

anterior horns at 24 weeks

A
  • should be less than 2 cm
40
Q

10 10 6

A
  • lateral ventricles posterior
  • cisterna magna
  • nuchal fold
41
Q

soft markers

A
  • individuals can be born

- won’t be harmful to baby

42
Q

biocular distance (orbital)

A
  • transverse image through both orbits as well as cranium
  • orbital distance changes with gestation
  • outer orbit to outer orbit
  • hypotelorism and hypertelorism
    + hyper to far
    + hypo to far
43
Q

all long bones

A
  • have to do right and left
  • to asses skeletal dysplasia
  • femur
  • radius and ulna
  • humerus
  • clavicles
  • chest circumference
44
Q

other measurement s

A
  • foot length for gestational age
  • phalanges for down syndrome
  • nasal bones for Down syndrome
45
Q

gestational size compared to dates

A
  • biometry plotted on graphs to assess for gestational size
  • plotted according to LMP to an early ultrasound
  • LGA and SGA reasons to assess fetal size
46
Q

under 10th percentile

A
  • not good
  • not in safe environment
  • very small
47
Q

over 90th percentile

A
  • sometimes gestational diabetes or genetics

- very large

48
Q

large for gestational age LGA

A
  • due to maternal obesity or gestational diabetes

+ GDM = abdomen grows at increased rate due to increased exposure to glucose

49
Q

macrosomia

A
  • weight >4000 grams
  • have increased morbidity and mortality because they are difficult to deliver
  • baby can become hypoglycaemic post delivery
50
Q

small for gestational age SGA

A
  • may be due to intrauterine growth restriction IUGR
  • IUGR due to
    + multiple pregnancy
    + placental insufficiency
    + chromosomal abnormalities
  • increased risk of fetal morbidity or mortality
51
Q

asymmetric IUGR

A
  • head normal size but abdomen small (shunting oxygen to brain)
  • usually due to a placenta insufficiency
  • 75% of all IUGR
  • occurs in 3rd trimester
52
Q

symmetric IUGR

A
  • all measurements small
  • usually due to chromosomal abnormality
  • 25% of all IUGR
  • occurs in 2nd trimester

Ob/Gyne (24 decks)

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