Obstetric ultrasonography, or prenatal ultrasound, is the use of medical ultrasonography in pregnancy, in which sound waves are used to create real-time visual images of the developing embryo or fetus in the uterus.

1. OBSTETRIC
ULTRASOUND
BY: MUKESH SAH
POST GRADUATE MEDICAL INTERN
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2. Ultrasound
orefers to sound waves traveling at a frequency above
20,000 hertz (cycles per second).
oTransducers use wide-bandwidth technology to perform
over a range of frequencies.
o In 2nd trimester, a 4- to 6-megahertz abdominal
transducer is often in close enough proximity to the fetus
to provide precise images.
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3. TRANSABDOMINAL
ULTRASOUND
◦ Lower frequency, lower resolution image
◦ Curved linear transducer
◦ Better visualized with full bladder
◦ Can see coronal and sagittal views of
organs and fetus
Bladder
Uterus
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4. TRANSVAGINAL ULTRASOUND
◦ Higher frequency, higher resolution image
◦ Endocavitory probe
◦ Better visualized with empty bladder
◦ Can see sagittal or coronal view of uterus
◦ RULE OF THUMB: if possible attempt transabdominal before considering transvaginal to avoid more
invasive procedure.
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5. All sonography machines are required to display two indices:
1. Thermal Index
a measure of the relative probability that the examination may raise the
temperature, potentially enough to induce injury.
2. Mechanical Index
a measure of likelihood of adverse effects related to rarefractional
pressure, such as cavitation—which is relevant only in tissues that
contain air.
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6. The following guidelines may
help avert injury:
1. Position the patient on the examination table close to you, so that your
elbow is close to your body, with less than 30 degrees shoulder abduction,
keeping your thumb facing up.
2. Adjust the table or chair height so that your forearm is parallel to the floor.
3. If seated, use a chair with back support, support your feet, and keep ankles
in neutral position. Do not lean toward the patient or monitor.
4. Face the monitor squarely and position it so that it is viewed at a neutral
angle, such as 15 degrees downward.
5. Avoid reaching, bending, or twisting while scanning.
6. Frequent breaks may avoid muscle strain. Stretching and strengthening
exercises can be helpful.
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7. Indications for Sonography before
14 weeks’ gestation
Confirm an intrauterine pregnancy
Evaluate a suspected ectopic pregnancy
Define the cause of vaginal bleeding
Evaluate pelvic pain
Estimate gestational age
Diagnose or evaluate multifetal gestations
Confirm cardiac activity
Modified from the American Institute of Ultrasound in Medicine, 2013a.
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8. Indications for Sonography before
14 weeks’ gestation
Assist chorionic villus sampling, embryo transfer, and localization and
removal of an intrauterine device
Assess for certain fetal anomalies such as anencephaly, in high-risk
patients
Evaluate maternal pelvic masses and/or uterine abnormalities
Measure nuchal translucency when part of a screening program for
fetal aneuploidy
Evaluate suspected gestational trophoblastic disease
Modified from the American Institute of Ultrasound in Medicine, 2013a.
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9. Indications for Second or
Third Trimester Ultrasound
Examination
MATERNAL INDICATIONS
Vaginal bleeding
Abdominal/pelvic pain
Pelvic mass
Suspected uterine
abnormality
Suspected ectopic
pregnancy
Suspected molar pregnancy
Suspected placenta previa
and subsequent surveillance
FETAL INDICATIONS
Gestational age estimation
Fetal-growth evaluation
Significant uterine
size/clinical date discrepancy
Suspected multifetal
gestation
Fetal anatomical evaluation
Fetal anomaly screening
Assessment for findings that
may increase the aneuploidy
risk
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10. Indications for Second or Third
Trimester Ultrasound Examination
MATERNAL INDICATIONS
Suspected placental
abruption
Preterm premature rupture
of membranes and/or
preterm labor
Cervical insufficiency
Adjunct to cervical cerclage
Adjunct to amniocentesis or
other procedure
Adjunct to external cephalic
version
FETAL INDICATIONS
Abnormal biochemical markers
Fetal presentation determination
Suspected hydramnios or
oligohydramnios
Fetal well-being evaluation
Follow-up evaluation of a fetal
anomaly
History of congenital anomaly in
prior pregnancy
Suspected fetal death
Fetal condition evaluation in late
registrants for prenatal care
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11. Components of Standard
Ultrasound Examination by First
Trimester
Gestational sac size, location, and number
Embryo and/or yolk sac identification
Crown-rump length
Fetal number, including amnionicity and chorionicity of multifetal
gestations
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12. Components of Standard
Ultrasound Examination by First
Trimester
Embryonic/fetal cardiac activity
Assessment of embryonic/fetal anatomy
appropriate for the first trimester
Evaluation of the maternal uterus, adnexa, and
cul-de-sac
Evaluation of the fetal nuchal region, with
consideration of fetal nuchal translucency
assessment
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13. Gestational Sac (GS):
◦ Visible at 4-5wks GA with transvaginal US
◦ Visible at 6 wks GA with transabdominal US
◦ echogenic ring with anechoic center within uterine cavity
◦ Measure by Mean Sac Diameter: average dimensions of
width/length/height of sac
◦ GS size increases by about 1mm/day in early pregnancy
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14. Gestational Sac (GS):
Yolk Sac: bright ring with anechoic center located inside GS seen at 5wk GA.
Fetal Pole: represents fetal development at somite stage. Can be seen by
transvaginal US as thickening of yolk at 6wks GA.
Fetal heart beat : usually seen around the time fetal pole is present, further
confirming viability
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15. 2nd and 3rd Trimester
sonography
1. Standard sonographic examination
anatomical structures that should be evaluated during
the examination
assessed after approximately 18 weeks
2. Specialized sonographic examinations
targeted examination is a detailed anatomical survey
performed
when an abnormality is suspected on the basis of
standard examination
3. Limited sonographic examination
operform to address a specific clinical question including
amnionic fluid volume assessment, placental location,
or evaluation of fetal presentation or viability
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16. Components of Standard
Ultrasound Examination by 2nd
and 3rd Trimester
Fetal number, including amnionicity and chorionicity of multifetal
gestations
Fetal cardiac activity
Fetal presentation
Placental location, appearance, and relationship to the internal
cervical os, with documentation of placental cord insertion site
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17. Components of Standard
Ultrasound Examination by 2nd
and 3rd Trimester
Amnionic fluid volume
Gestational age assessment
Fetal weight estimation
Fetal anatomical survey, including documentation of technical
limitations
Evaluation of the maternal uterus, adnexa, and cervix when
appropriate
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18. Standard
Examination of Fetal
Anatomy
Head, face, and neck
Lateral cerebral ventricles
Choroid plexus
Midline falx
Cavum septum pellucidi
Cerebellum
Cisterna magna
Upper lip
Nuchal fold
at 15–20weeks
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19. Minimal Elements of a Standard
Examination of Fetal Anatomy
Chest
Four-chamber view
Left ventricular
outflow tract
Right ventricular
outflow tract
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20. Minimal Elements of a Standard
Examination of Fetal Anatomy
Abdomen
Stomach—presence, size, and situs
Kidneys
Urinary bladder
Umbilical cord insertion into fetal abdomen
Umbilical cord vessel number
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21. Minimal Elements of a Standard
Examination of Fetal Anatomy
Spine
Cervical, thoracic, lumbar, and sacral spine
Extremities
Legs and arms
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22. Minimal Elements of a Standard
Examination of Fetal Anatomy
Fetal sex
In multifetal gestations and when medically indicated
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23. Guidelines for Nuchal
Translucency (NT) Measurement
The margins of NT edges must be clear enough for proper caliper placement
The fetus must be in the midsagittal plane
The image must be magnified so that it is filled by the fetal head, neck, and
upper thorax
The fetal neck must be in a neutral position, not flexed and not
hyperextended
The amnion must be seen as separate from the NT line
Electronic calipers must be used to perform the measurement
The + calipers must be placed on the inner borders of the nuchal space with
none of the horizontal crossbar itself protruding into the space
The calipers must be placed perpendicular to the long axis of the fetus
The measurement must be obtained at the widest space of the NT
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24. Nuchal Translucency
Measured during 11-14 wks gestational age
Seen on sagittal image as increased subcutaneous non-septated fluid in
posterior fetal neck
◦ sequential screening with NT: 82-87%
◦ NT alone: 64-70%
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25. Fetal Biometry
The estimated gestational age from the crown-rump
length.
Formulas are similarly used to calculate estimated
gestational age and fetal weight from measurements
of the
biparietal diameter head
abdominal circumference
femur length
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26. crown rump length (CRL)
◦ Approximately estimates Gestational Age from 7-12wks gestation
◦ Measure longest length of embryo
A Rule of thumb of estimating GA:
6wks + CRL(mm) = 6wks+days
Estimating due date:
◦ For 1st trimester if GA measures within 7days of EDD by LMP then do not
change EDD
◦ For 2nd trimester if GA measures within 10days of EDD by LMP  then do not
change EDD
◦ If ultrasound provides EDD more/less than the 7 or 10 days, then EDD is changed
to ultrasound EDD
◦ Once GA confirmed with first trimester CRL, EDD should NOT be changed in
further CRL measurements
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27. Fetal Biometry
BIPARIETAL DIAMETER FEMUR LENGTH
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28. Fetal Biometry
Abdominal Circumference
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29. Amnionic Fluid
Amnionic fluid volume evaluation is a component of every second or third
trimester sonogram.
The normal range for single deepest pocket that is most commonly used is2
to 8 cm
Oligohydramnios
that the volume is below normal range, The sonographic diagnosis is usually
based on an AFI ≤ 5 cm or on a single deepest pocket of amnionic fluid ≤ 2
cm
Hydramnios or polyhydramnios—
is defined as amnionic fluid volume above normal
the ultrasound transducer is held perpendicular to the floor and parallel to
the long axis of the pregnant woman.
The uterus is divided into four equal quadrants—the right- and left-upper
and lower quadrants,respectively.
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30. Amniotic Fluid Index
The normal range for AFI that is most commonly used is 5 to 24cm, with
values above and below.
The AFI is the sum of the single deepest pocket from each quadrant.
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31. ABNORMAL FETAL ANATOMY
Acrania Anencephaly
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32. ABNORMAL FETAL ANATOMY
Encephalocele Ventriculomegaly
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33. ABNORMAL FETAL ANATOMY
Myelomeningocele Alobar holoprosencephaly
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34. ABNORMAL FETAL ANATOMY
Dandy-Walker Sacrococcygeal malformation
teratoma
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35. ABNORMAL FETAL ANATOMY
Face and Neck
Micrognathia Cleft lip/palate
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36. ABNORMAL FETAL ANATOMY
Neck
Cystic Hygroma
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37. ABNORMAL FETAL ANATOMY
Thorax
Congenital diaphragmatic hernia
Congenital high
airway obstruction
sequence
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38. Components of Fetal
Echocardiography
Basic imaging parameters
Evaluation of atria
Evaluation of ventricles
Evaluation of great vessels
Cardiac and visceral situs
Atrioventricular junctions
Ventriculoarterial junctions
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39. Components of Fetal
Echocardiography
Four-chamber view
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40. Components of Fetal
Echocardiography
Left ventricular OT Right ventricular OT
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41. Components of Fetal
Echocardiography
Three vessel and trachea view
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42. Components of Fetal
Echocardiography
High axis view Low axis view
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43. Components of Fetal
Echocardiography
Aortic arch view Ductal arch view
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44. Components of Fetal
Echocardiography
Superior and Inferior vena cavae views
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45. ABNORMAL FETAL ANATOMY
Heart
VSD AVSD
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46. Motion-mode or M-mode
imaging
linear display of cardiac cycle events, with time on the x-axis and
motion on the y-axis
used to measure fetal heart rate If there is an abnormality of heart rate
or rhythm
permits separate evaluation of atrial and ventricular waveforms
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47. Motion-mode or M-mode
imaging
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48. ABNORMAL FETAL ANATOMY
Abdominal wall
Gastroschisis Omphalocoele
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49. ABNORMAL FETAL ANATOMY
Renal
Renal pelvis dilatation Duplicated renal
collecting system
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50. ABNORMAL FETAL ANATOMY
Skeletal Abnormalities
Osteogenesis imperfecta Talipes
Equinovarus
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51. THREE- AND FOUR-DIMENSIONAL
SONOGRAPHY
3-D volume is acquired that may be rendered to display images of any
plane— axial, sagittal, coronal, or even oblique—within that volume.
Sequential “slices” can be generated
Technique applications include
evaluation of intracranial anatomy in the sagittal plane (corpus
callosum, palate and skeletal system)
Four-dimensional (4-D) sonography/Real-time 3-D
-allows rapid reconstruction of the
rendered images to convey the impression
that the scanning is in real time. Improves visualization of cardiac
anatomy.
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52. Ultrasonography
3D
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53. Ultrasonography
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54. Doppler Ultrasound
When sound waves strike a moving target, the frequency of the waves
reflected back is shifted proportionate to the velocity and direction of
that moving target—a phenomenon known as the Doppler shift.
Because the magnitude and direction of the frequency shift depend on
the relative motion of the moving target, Doppler can be used to
evaluate flow within blood vessels.
Doppler waveform and describes
The simplest is the systolic-diastolic ratio (S/D ratio), which compares
the maximal (or peak) systolic flow with end-diastolic flow to evaluate
downstream impedance to flow.
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56. Doppler Ultrasound
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57. Doppler Ultrasound
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58. Doppler Ultrasound
MCA Doppler
An early stage
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59. Doppler Ultrasound
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60. THANK YOU
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