Obstetric Ultrasound

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Obstetric Ultrasound

• Felipe Moretti, MD
• Griff Jones, MD, FRCS
• Assistant Professor Uottawa
• Maternal Fetal Medicine Division

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• About 4 of all pregnancies are complicated by
  one or more major fetal malformations, 2 by a
  fetal genetic disorder, 1 by miscarriage after
  the first trimester, and another 1 result in
  infant death in the first year of life.
• Obstetrical and Gynecological Survey, 2008.

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What is Prenatal Diagnosis?

• Aneuploidy Downs Syndrome
• Anomalies Spina bifida / NTD
• Fetal disease Iso-immunisation (Rh)
• Infection
• Cardiac arrythmias

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Obstetric Ultrasound

• First Trimester scan
• Second trimester
• Third trimester

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Obstetric Ultrasound

• First Trimester scan
• Determine Gestational age
• Viability
• Number of embryos or fetus
• Intrauterine pregnancy

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First Trimester scan

• Determine Gestational age CRL (Crump Rump
  Length)

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Normal Early Pregnancy
Fetal cardiac activity present
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Viability
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Viability
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First Trimester scan

• Number of embryos or fetus

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Intrauterine pregnancy or Ectopic pregnancy
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First Trimester scan

• IPS ( Integrated Prenatal Screen)
• Combine test with Maternal blood work and
  Ultrasound
• Blood work and US at 11-136 days pregnancy
  associate plasma protein-A (PAAP-A) and free-hCG
  plus NT
• Blood work at 15-19 weeks AFP, estriol and
  inhibin.

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Fetal Structural Anomalies

• Anatomy review done at 18 - 20 weeks
• Striking a balance
• Adequate visualisation of fetal structures
• Allow adequate time for further investigation
• Leave parents the option of not continuing the
  pregnancy
• Studies have shown a higher detection rate at 20
  weeks

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Nuchal Translucencia
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NT
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IPS result
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Second trimesterMorphology scan at 18-20 weeks
Body System Detection Rates
Abdominal Wall 95
CNS 80
Renal 60
Skeletal 30
Cardiac 20 to 50
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Difficulties in Imaging
Obesity
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Fetal Position

• Apposing structures
• Shadowing
• Orientation
• TV scanning
• Heart
• Head
• Engagement

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Amniotic Fluid Volume
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Congenital Cardiac Anomalies

• Detection rate remains poor
• 25-50
• Technically difficult
• Complex anatomy
• Movement
• Function changes at birth

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Small Rapidly Moving Target
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Level 2 Ultrasound for Maternal Valproate Exposure
Normal genetic sonogram Normal extended
anatomy review
Baby discovered to have Downs Syndrome at birth
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Prenatal ultrasound is not a perfect science

• Risks are modified
• Nothing is 100

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Normal Fetal Spine
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What is wrong with this spine?
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Abnormal Lower Spine
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What if you cant see the spine?
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Other ways to make the diagnosis
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Ventriculomegaly
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What else Ultrasound can help us in the 2nd and
3rd trimester?

• Placenta Location
• Anterior/Posterior/Fundal/Lateral
• Previa or non-previa
• Presentation
• Cephalic
• Breech
• Transverse

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How is the Baby Doing?Fetal Well Being
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Fetal Growth

• There is a higher morbidity and mortality in
  babies that are small for gestational age
• Unfortunately, most babies weighing lt10th centile
  are normally grown and a significant number of
  IUGR babies have birthweights gt10th centile

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Fetal Measurement 2nd and 3rd trimester

• Fetal Head BPD and HC
• Fetal Abdomen AC
• Femur Length
• Estimate Fetal Weigth (EFW)

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EFW 10 to 90 centile
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Variability in Weight Estimates

• Technical / image quality
• Caliper placement
• Numerous mathematical models
• Log weight 3-1.74920.0166(BPD 0.0046AC
  0.00002646ACBPD)
• All tend to be poor at weight extremes
• Aim for /- 10 in 90 estimates

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Ultrasound Assessment of Fetal Behaviour

• Significant Canadian contribution to the field
• Followed on from the introduction of real-time
  ultrasound
• Led to the development of the Biophysical Profile
  (BPP)

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Fetal Breathing

• Occurs 30 of time at term
• Clusters lasting 20 minutes every 60-90 minutes
• Apnea episodes lasting up to 2 hours occasionally
  seen

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Fetal Movement

• Fetus moves 10 of
• time at term
• Average of 31
• movements per hour
• No movement occasionally occurs
• for up to 75 minutes

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Fetal Tone

• One episode of extension and return to flexion in
  30 min
• More recent modification to reflect fine motor
  activity
• Hand opening / closing
• Mouth opening / closing

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Biophysical Profile
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Oligohydramnios

• Three pathologies to consider
• Renal tract anomaly
• Rupture of membranes
• especially if very preterm
• Renal hypoperfusion
• Compensatory mechanism to maintain blood flow to
  heart and brain
• Analagous to oliguria in sick adults
• Seen in IUGR

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Oligohydramnios and Perinatal Mortality
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Amniotic Fluid Assessment

• One measure
• 2 x 2 pocket
• Single deepest pool
• Four quadrants
• AFI
• Subjective impression

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Doppler
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Umbilical Artery Doppler
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Abnormal Umbilical Artery Dopplers
Normal
Absent EDF
4x PNM
Reversed EDF
11x PNM
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Antepartum Haemorrhage

• Abruption
• By the time an abruption can be seen on
  ultrasound, there will often be haemodynamic
  effects on mother or fetus
• Praevia
• TV ultrasound is diagnostic method of choice

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The principle role of ultrasound in antepartum
haemorrhage is to exclude placenta praevia
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Classification of Placenta Previa
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Invasive Diagnostic Tests
CVS 10 to 14 weeks (earlier result) Amniocentes
is 15 weeks Cordocentesis 18 weeks (quicker
result)
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Amniocentesis

• Risk of miscarriage 1 in 400
• Done at 15 weeks
• 1 chance of amniotic fluid leakage post-procedure

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CVS

• Essentially is a placental biopsy
• Larger diameter needle
• More uncomfortable
• Higher miscarriage rate (1)
• Technically more challenging
• Can be done after 10 weeks

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Thank You