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OBSTETRIC ULTRASOUND TECHNIQUES
FETAL AGE ESTIMATION
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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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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 women5
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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
Transducer
Transmitted pulse
Received pulse
Object
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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– 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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Common Uses of Obstetric USG 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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Common Uses of Obstetric USG cont
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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Trans Abdominal Ultrasound (TAS)
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• 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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Trans Vaginal Ultrasound (TVS)
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• 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
• 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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Trans Vaginal Ultrasound (TVS) cont
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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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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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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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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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Obstetric USG in 1st Trimester
• Identification of Gestational sac and Embryo
24First trimester fetus and yolk sac
• Recording the presence or absence of fetal life
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Obstetric USG in 1st Trimester cont
Embryo 4 weeks
• Identification and documenting the fetal number
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Two gestational sacs, each containing a yolk sac
Obstetric USG in 1st Trimester cont
• Evaluation of Uterus and Adnexal structures
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Obstetric USG in 1st Trimester cont
Uterus and cervical plug
• Measurement of Nuchal Translucency
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Obstetric USG in 1st Trimester cont
Nuchal Translucency
29Triplet with sub-chorionic bleeding
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Twin pregnancy28 mm CRL in 10 weeks
• Fetal life, number and presentation• Amount of amniotic fluid
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Obstetric USG in 2nd and 3rd Trimester
• Record Placental localization• Establishment of fetal age and growth by fetal
biometry including– Bi-parietal Diameter– Head Circumference– Femur Length– Abdominal Circumference
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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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Obstetric USG in 2nd and 3rd Trimester cont
35Fetal Cardiac Structure
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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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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• 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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Fetal Age Estimation in 2nd & 3rd Trimester
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Bi-parietal diameter and head circumference measurements
Fetal Age Estimation in 2nd & 3rd Trimester
41Bi-parietal Diameter
• 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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Fetal Age Estimation in 2nd & 3rd Trimester
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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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Thank You
Q & A
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