This document discusses techniques for fetal age estimation using obstetric ultrasound. It begins with an introduction to obstetric ultrasound, describing its history and uses. It then covers ultrasound technology and transducer principles. The main uses of obstetric ultrasound are established as determining fetal number, position, growth and detecting abnormalities. Examination types like transabdominal and transvaginal ultrasound are described. The document outlines fetal assessment and measurements used in each trimester to estimate gestational age, including crown-rump length in the first trimester and biometric parameters like biparietal diameter in later stages. Fetal age estimation is emphasized as fundamental to obstetric care, with ultrasound providing a reliable method.

1. OBSTETRIC ULTRASOUND
TECHNIQUES
FETAL AGE ESTIMATION
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2. 2

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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4. 4

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

7. Transducer
Received pulse
Transmitted pulse
Object

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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13. 13

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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16. 16

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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18. 18

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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20. 20

21. Three-dimensional USG (3-D)
• 3-Dimensional “cleaner” image of the scanning
• Transducer captures series of images
• 3-D processing done by Computer
• Significant improvement in identifying
– Cleft lips
– Spina bifida
– Polydactyl
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22. 22

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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29. Triplet with sub-chorionic bleeding
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30. 30

31. Twin pregnancy
28 mm CRL in 10 weeks
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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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35. Fetal Cardiac Structure
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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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41. Bi-parietal Diameter
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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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45. Thank You
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46. Q&A
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