3. Sequence
• Introduction to Obstetric Ultrasound
• Technology
• Common Uses
• Types of USG
• Indications of Ultrasound Examination
• Application of Ultrasound in Trimesters
• Fetal Age Estimation
• Conclusion
• Q & A session
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5. Introduction to Obstetric Ultrasound
• Use of ultrasound scans in pregnancy
• Introduced in late 1950s
• Provision of good information about the fetus
and its environment
• Determining early intervention or conservative
management
• Safe, non-invasive, accurate, and cost-effective
investigation in fetus
• Important role in care of pregnant women
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6. Ultrasound Technology
• Principle of SONAR, used by bats and ships
• Generation of high-frequency sound waves
through a transducer
• Pulsed sound waves penetrate till structures of
different tissues densities is reached
• Reflected energy to the transducer is amplified
and displayed on a screen
• Detection of breathing, cardiac actions and vessel
pulsations through real-time ultrasonography 6
8. Common Uses of Obstetric USG
• Obstetrical ultrasound is a useful clinical test to:
– Establish the presence of a living embryo/fetus
– Estimate the age of the pregnancy
– Diagnose congenital abnormalities of the fetus
– Evaluate the position of the fetus
– Evaluate the position of the placenta
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9. Common Uses of Obstetric USG
cont
– Determine if there are multiple pregnancies
– Determine the amount of amniotic fluid around the
baby
– Check for opening or shortening of the cervix or
mouth of the womb
– Assess fetal growth
– Assess fetal well-being
– Suspected hydatidiform mole
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10. Common Uses of Obstetric USG
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cont
Suspected fetal death
Suspected uterine abnormality
UCD localization
Ovarian follicle development surveillance
Biophysical profile after 28 weeks of gestation
Observation of intra-partum events
Suspected poly- or oligohydramnios
Suspected abruptio placenta
Adjunct to external version from breech to vertex
presentation
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11. Types of Ultrasonography
• Trans Abdominal Ultrasonography (TAS)
• Trans Vaginal Ultrasonography (TVS)
• Doppler Ultrasound
• Tissue Harmonic Imaging (THI)
• Three-dimensional Ultrasound (3-D USG)
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12. Trans Abdominal Ultrasound (TAS)
• Major technique for imaging in 2nd and 3rd trimester
• Patient to have full bladder because
– Pushes the uterus out of the pelvis
– Provides an acoustic window
– Displaces pelvic bowel loop superiorly
• Real-time ultrasound equipment includes:
– Sector transducers, when access is limited
– Linear curved array transducers, for less distortion
and greater field of view
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14. Trans Vaginal Ultrasound (TVS)
• Method of choice for
– Monitoring infertility disorders
– Diagnosis of ectopic pregnancy
– Differentiation of normal and abnormal 1st
trimester pregnancy
– Diagnosis of congenital anomalies in 2nd trimester
• Patient to have empty bladder because
– Uterus will be pushed posteriorly out of the field
of view of the transducer
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15. Trans Vaginal Ultrasound (TVS)
cont
• Specially designed high frequency transducers
• Higher resolution images
• Favorable for obese patients or in early stage of
pregnancy
• Limitations include
– Reduced beam penetration
– More invasive nature of the technique
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17. Doppler Ultrasonography
• Most widely employed for detection of:
– Fetal cardiac pulsation
– Pulsation in various fetal blood vessels
• Doppler waveform for useful information about
intra-uterine growth retardation
• Use remains controversial due to increased power
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19. Tissue Harmonic Imaging (THI)
• Processing of lower amplitude, higher frequency
waveforms accompanying fundamental frequency
• Lesser clutter and scatter
• Better visualization of fetal structure
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23. Application of Ultrasound in Trimesters
• First Trimester
– Commonly performed at 9-12 weeks
• 2nd and 3rd Trimester
– Commonly performed at 18-20 weeks
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24. Obstetric USG in 1st Trimester
• Identification of Gestational sac and Embryo
First trimester fetus and yolk sac
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25. Obstetric USG in 1st Trimester
cont
• Recording the presence or absence of fetal life
Embryo 4 weeks
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26. Obstetric USG in 1st Trimester
cont
• Identification and documenting the fetal number
Two gestational sacs,
each containing a yolk sac
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27. Obstetric USG in 1st Trimester
cont
• Evaluation of Uterus and Adnexal structures
Uterus and cervical plug
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28. Obstetric USG in 1st Trimester
cont
• Measurement of Nuchal Translucency
Nuchal
Translucency
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32. Obstetric USG in 2nd and 3rd Trimester
• Fetal life, number and presentation
• Amount of amniotic fluid
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33. Obstetric USG in 2nd and 3rd Trimester cont
• Record Placental localization
• Establishment of fetal age and growth by fetal
biometry including
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Bi-parietal Diameter
Head Circumference
Femur Length
Abdominal Circumference
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34. Obstetric USG in 2nd and 3rd Trimester cont
• Evaluation of the uterus and adnexal structures
• Evaluation of fetal anatomic structures :
– Cerebellum and Cerebral ventricles
– Spine
– Stomach-bowel, abdominal wall at the area of the
umbilical cord insertion
– Bladder and kidney
– All four Limbs
– Four chamber view of the heart
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36. Fetal Age Estimation
• Assessment of gestational age is fundamental to
obstetric care
• Ultrasound is a reliable method for establishing
the length of pregnancy
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37. Fetal Age Estimation in 1st Trimester
• Identification of Gestational sac
– Correlation of MSD and CRL with menstrual age
• Visualizing of Embryo by TVS and TAS
– Estimation of gestational age by crown-rump length
• Nuchal Translucency assessment in 1st trimester
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39. Fetal Age Estimation in 2nd & 3rd Trimester
• Bi-parietal diameter measurement
– Around 09 weeks until end of pregnancy
• Head Circumference measurement
– Gestational age prediction when abnormal skull shape
– Measured on same plane as Bi-parietal diameter
• Abdominal Circumference measurement
– Measurement similar to head circumference
– Less accurate for establishing gestational age
– Perpendicular plane to the long axis of fetus
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40. Fetal Age Estimation in 2nd & 3rd Trimester
Bi-parietal diameter and head circumference measurements
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42. Fetal Age Estimation in 2nd & 3rd Trimester
• Femur measurement
– Only long bone measured routinely
– Fetal age assessment when head cannot be utilized
for Bi-parietal diameter
• Multiple Fetal growth parameters
– Single parameter increases variability in predicting
fetal age in 3rd trimester
– Variability reduction through parameter combination
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44. Conclusion
• Fetal age estimation is fundamental to obstetric
care
• Ultrasound is a reliable method for establishing
the length of pregnancy and in this way can
improve obstetric care
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