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Principals of USS > USS > Flashcards

USS Flashcards

1
Q

How to measure EFW? (Hadlock formula)

A

Hadlock B and C multi-parameter formulas are the most commonly used in clinical practice. Hadlock B (HC, AC and FL) is encouraged, as head circumference measurements are less prone to error due to fetal moulding, compared to those that use bi-parietal diameter.

Hadlock B and C have been shown to be most accurate for fetal weights between 2500-4000g

NB. Hadlock D includes BPD, HC, AC , FL

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2
Q

Systematic screening technique (order to review things)

A
  • Identify bladder, vagina and cervix
  • Identify presenting part of fetus
  • Rotate probe to transverse andslide to umbilicus
  • Identify fetal HR and document motion using M-Mode
  • Check placental position
  • Check amniotic fluid
  • Perform measurements
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3
Q

Placental site assessment

A
  • Identify ectocervix and internal os
  • fully define placental site in longtitudinal and transverse views of the whole uterus
  • If lower margin of placental edge not seen, needs transvaginal scan
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4
Q

Abnormally sited placenta definitions:

  • Major placenta praevia
  • Minor Placenta praevia
  • Succenturiate lobe
A
  • Major- placenta covers internal os
  • Minor- Placental edge <2cm from internal os or reaching it but doesn’t cover it
  • Succenturiate lobe- accessory placental tissue separate to main placental mass but connected by a fetal vessel
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5
Q

Two equations to measure EFW?

A

Shepard - BPD and AC

Hadlock - HC, AC and FL (more accurate)

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6
Q

Normal AFI measurement?

Normal DVP measurement?

A 
AFI = 5-25cm 
DVP = 2-8cm (or 10cm)

(although dependent on gestational age)

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7
Q

How to measure a SDP?

A

Ensure transducer parallel to bed
Identify deepest pocket - must be at least 1cm wide
Ensure no fetal parts in pocket
Apply colour doppler to ensure no loops of cord
Measure vertical depth of pocket
Record largest SDP measurement

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8
Q

SDP vs AFI measurement?

A
  • No evidence that one is better than the other for preventing adverse perinatal outcomes
  • AFI results in increased diagnosis of oligo, IOL and CS for fetal distress without improvement in Apgar score, UA pH<7.1 or improvement in perinatal outcome
  • SDP is easier, quicker and more reproducible between practitioners

Therefore measurement should be based on SDP

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9
Q

When should Umbilical artery doppler be measured?

A
  • SGA/FGR pregnancies
  • Hypertension
  • No role in low risk
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10
Q

What does umbilical artery measure?

A
  • Measurement of placental resistance

- Gestational age dependent, resistance decreases with advancing gestation in normal pregnancy

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11
Q

Technique for measuring UAPI

A
  • free loop of cord away from insertions
  • no fetal body/limb or breathing
  • Identify UA with colour doppler
  • MEasure FVW with pulsed doppler
  • Set gate size to measure entire vessel
  • Display arterial and venous waveforms simultaneously
  • Measurement of PI preferable over S/D
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12
Q

Patterns of UA flow:

  • Normal
  • AEDF
  • REDF
A
  • Nomal: positive flow during diastole
  • increased placental resistance results in a progression to AEDF then REDF which are both associated with increased perinatal mortality
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13
Q

Surveillance of FGR

A
  • UAPI should be measured as this reduces perinatal mortality
  • EFW and UAPI every 2 weeks if UAPI normal
  • If UA abnormal then consider twice weekly UAPI
  • Daily dopplers if AEDF/REDF
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14
Q

Indications for MCA

A
  • FGR/SGA

- Other: fetal anaemia e.g. RBC alloimmunisation, monitoring for monochorionic twins

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15
Q

Measuring MCA

A
  • Part of circle of willis

- Normal- high resistance

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16
Q

What does MCA mean?

A
  • Sign of chronic hypoxia but not acidaemia or adverse outcome
  • In preterm FGR, MCA shouldn’t be used for earlier delivery
  • But delivery should be no later than 37/40
  • In term SGA/FGR with normal UAPI but abnormal MCA- should be used to time delivery
17
Q

Ductus venosus- indications and what does it mean?

A

Indications:

  • Preterm FGR/SGA
  • Fetal abnormality e.g. hydrops/cardiac anomaly

What does it mean?

  • Gives information re cardiac redistribution
  • Abnormal flow indicated by a reversed flow during atrial contraction
  • Associated with fetal acidaemia and imminent fetal death
18
Q

Components of normal DV waveform

A
  • S wave: ventricular systole and atrial relaxation
  • D wave: ventricular diastole: passive filling
  • A wave: ventricular diastole: atrial contraction

Abnormal: reversed ‘a’ wave

Abnormal DV should be used to time deliver in preterm FGR fetuses

19
Q

Timeline for fetal response to uteroplacental insufficiency:

A
  • Reduced growth
  • Fetal hypoxia -> Abnormal arterial flows
  • Arterial redistribution ->Reduced amniotic fluid
  • Fetal acidaemia -> abnormal venous flows
  • Severe fetal acidaemia-> Abnormal BPP
20
Q

The most significant biometric predictor of fetal size is

Select one:

a. the femur length
b. the biparietal diameter
c. the abdominal circumference
d. the head circumference

A

D

21
Q

Estimated fetal weight in the second and third trimester is

Select one:

a. diagnostic of fetal growth restriction if less than the 10th centile
b. an estimation of fetal size
c. useful to reduce the number of SGA neonates delivered in low risk pregnancy
d. an estimation of fetal growth

A

B

22
Q

Intergrowth 21st Project is the first prospective multicentre multiethnic cohort study of fetal biometry which provides

Select one:

a. International standards for fetal growth recommended for interpretation of estimated fetal weight across populations
b. International standards for fetal growth that reduce perinatal mortality
c. International standards for fetal growth recommended for interpretation of fetal biometry across populations
d. International standards for fetal growth that customize for maternal factors

A

C

23
Q

Amniotic fluid volume is a routine assessment in the third trimester. When comparing pregnancy outcome following measurement of the amniotic fluid index (AFI) with measurement of a single deepest vertical pool (SDVP), which of the following statements is true?

Select one:

a. Increased rate of Caesarean delivery for “fetal distress” with SDVP
b. Decreased rate of ultrasound diagnosis of oligohydramnios with AFI
c. Increased rate of induction of labour with SDVP
d. Similar rate of umbilical artery cord pH<7.1 with both measurements

A

D

24
Q

Which of the following statements is correct with respect to umbilical artery (UA) Doppler?

Select one:

a. Using UA Doppler has been shown to reduce perinatal mortality in preterm pregnancies complicated by fetal growth restriction
b. Using UA Doppler has been shown to reduce perinatal mortality in preterm pregnancies with oligohydramnios measured by a single deepest vertical pool
c. UA Doppler should be performed routinely during growth scans to screen for fetal growth restriction
d. UA Doppler is the most useful test at term to time delivery in fetal growth restriction

A

A

25
Q

An otherwise healthy woman at 30 weeks gestation with a growth restricted fetus should be delivered when regular surveillance identifies

Select one:

a. Abnormal ductus venosus flow
b. Severe oligohydramnios
c. Abnormal middle cerebral artery flow
d. Abnormal umbilical artery flow

A

B

Principals of USS (3 decks)

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