obstetric ultrasound - fetal age estimation

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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