The document discusses guidelines for performing a second trimester ultrasound examination. It describes the 6 components of the stepwise ultrasound exam: 1) fetal lie and presentation, 2) fetal cardiac activity, 3) number of fetuses, 4) placental localization, 5) amniotic fluid assessment, and 6) fetal biometry. Fetal biometric measurements taken include biparietal diameter, head circumference, abdominal circumference, and femur length. These measurements are used to determine gestational age and fetal growth.

1. Second Trimester Ultrasound
Hale T., O & G Yr-1 Resident,
Mekelle University,
College of Health Sciences, Dep't of OB-GYN
26 Jan 2016

2. Hale T., M.D., Resident Physician
• Contents
– Stepwise approach to second trimester
ultrasound examination
– Fetal biometeric measurements
– Fetal anomaly scan

3. Hale T., M.D., Resident Physician
• Objectives
– To understand the 6 components of
stepwise ultrasound exam in 2nd trimester
of pregnancy
– To be able to measure accurately the 4
standard biometric parameters for fetal
age and/or fetal growth (weight) assessment
– To understand principles and standardized
method of ultrasound examination for fetal
anatomy scan

4. Hale T., M.D., Resident Physician
1. Stepwise Approach
1. Fetal lie and presentation
2. Fetal cardiac activity
3. Number of fetuses in the uterus
4. Adequacy of aminotic fluid
5. Localization of the placenta
6. Fetal biometry

5. Hale T., M.D., Resident Physician
1. Fetal lie and presentation
– The orientation of the fetal spine to the
maternal spine
– Obtain midsagital view of the fetal spine
– Alternatively
• Fetal presentation cephalic or breech
–Longuitidinal
• Fetal presentation noncephalic nonbreech
–Oblique or transverse

6. Hale T., M.D., Resident Physician
Midsagittal View

7. Hale T., M.D., Resident Physician
Ultrasound in Obstetrics & Gynecology_ A Practical Approach - Clip 10.1.mp4

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10. Hale T., M.D., Resident Physician
2. Fetal Cardiac
Activity
Ultrasound in Obstetrics & Gynecology_ A Practical Approach - Clip 10.2.mp4
Ultrasound in Obstetrics & Gynecology_ A Practical Approach - Clip 10.3.mp4

11. Hale T., M.D., Resident Physician
3. Number of Fetuses
in the Uterus
– Mapping the entire
uterine cavity by
ultrasound
– Maintain the
transducer
perpendicular to the
floor

12. Hale T., M.D., Resident Physician
Transducer: Transverse

13. Hale T., M.D., Resident Physician
Transducer: Sagital

14. Hale T., M.D., Resident Physician
4. Placental Localization in the Uterus
Ultrasound in Obstetrics & Gynecology_ A Practical Approach - Clip 10.6.mp4

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5. Aminotic Fluid
Estimation
Ultrasoundin Obstetrics& Gynecology_A PracticalApproach - Clip10.7.mp4
Cord
Fetal parts
Transverse diameter of the pocket

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19. Hale T., M.D., Resident Physician
6. Fetal Biometry
– Biparietal diameter,
– Head circumference,
– Abdominal circumference and
– Femur length

20. Hale T., M.D., Resident Physician
2. Fetal Biometry
• Four fetal biometric measurements are
required for dating (determining
gestational age) and/or for estimating
fetal weight
– Biparietal Diameter (BPD),
– Head Circumference (HC),
– Abdominal Circumference (AC) and
– Femur Length (FL

21. Hale T., M.D., Resident Physician
– Fetal biometry refers to fetal age and
corresponds to the length of gestation
(dating) while size refers to the fetal weight
– BPD and FL provide the most accurate
assessment of gestational age in the second
trimester
– Biometric exam components enable for
systemic examination of the whole fetus

22. Hale T., M.D., Resident Physician
• Biparietal Diameter
– Should be measured in a cross-sectional view of
the fetal head at the level of the thalami
– Sonographic landmarks
• Midline Falx
• Thalami
• Symmetrical appearance of both cerebral
hemispheres
• Cavum Septae Pellucidi
• Insula
• No cerebellum visualized

23. Hale T., M.D., Resident Physician
• The BPD is the maximum diameter of a
transverse section of the fetal skull at the level
of the parietal eminences
– Measured from the outer edge of the proximal
skull to the inner edge of the distal skull at the
level of thalami & cavum septum pellucidum.

24. Hale T., M.D., Resident Physician
• BPD
– Easy to obtain
– More accurate than CRL
– More accurate in predcting EDD than LNMP

25. Hale T., M.D., Resident Physician
• Most accurate between 14 and 26 weeks
of gestation
– ±7 to 10 days
• Beyond 20 weeks
– Test performance diminishes
– Mid to late 3rd trimester
• Margin of error - three to four weeks

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28. Hale T., M.D., Resident Physician
• Measuring BPD in direct OA, OP or deep in
the maternal pelvis
– From a coronal plane of the head
– Tilting the woman into a 45° head-down
position
– Partially filling the maternal bladder
– Transvaginal imaging
– Otherwise
• GA from measurement of femur length can be
taken

29. Hale T., M.D., Resident Physician
• BPD measurements in breech and transverse
presentations
– Fetal head might be dolichocephalic (long
and narrow) in shape
• This produces a BPD measurement that is
artifactually small for gestational age

30. Hale T., M.D., Resident Physician
• BPD
– Not good biometer in the following cases
– These conditions affect the shape of the fetal skull
due to lateral compressive forces
• Fetal head shape abnormality (dolichocephaly
/brachycephaly)
• Breech and trasverse presentation,
• Oligohydramnios,
• PROM,
• NTD
– In these cases measure
• Cephalic Index (CI) =(BPD/OFD)x100
• 80 +/-5

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Plane of section that intersects both
the third ventricle and thalami

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• Problems
– Incorrect angle
– Incorrect rotation
– Incorrect level
– Midline not horizontal

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• Head Circumference
– Accuracy is within one week prior to 20
weeks of gestational age
– Test performance falls in the second half of
pregnancy
– In the late 3rd trimester the marigin of error
can be 3-4 weeks

35. Hale T., M.D., Resident Physician
• Possible views for measurement
• Thalami view
–Prefered by most literatures
• Ventricular view
–For ventricular exams

36. Hale T., M.D., Resident Physician
– There are three options for the
measurement of the HC
• The ellipse method
–Occiput to Synciput
• The 2-diameter method
– HC = 3.14 (BPD + OFD)/2
»Both BPD and OFD measured from
outer to outer
• The trace method

37. Hale T., M.D., Resident Physician
• Principles of measurement
– Obtained by placing the cursors on the
outer margins of the calvarium bilaterally
• Outer-outer
– Avoid including the skin thickness
– Using the computerized ellipse function

38. Hale T., M.D., Resident Physician
HC measuring through thalami view

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• Measuring TCD
– Suboccipitobregmatic view landmarks
• Anterior horns of the lateral ventricles
• Cavum
• Cerebellum

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– Method
• At 90 degree to the long axis of the
crebellum
• Outer-outer
• TCD in mm equivalent to numerically
equivalent to the number of weeks of
gestation of the pregnancy in 2nd
trimester of pregnancy
• Reconciles when BPD and HC disagree

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HC measuring through lateral ventricle view
Two Diameter

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Ellipse method

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• Abdominal Circumference
– Lower ability to predict gestational age
– Often used for estimations of fetal weight
and interval growth evaluations
– Important for gestational age determination
if cranial or limb abnormalities exist

46. Hale T., M.D., Resident Physician
• Abdominal Circumference
– Measured on a transverse section of the
upper fetal abdomen
– Sonographic landmarks
• Circular cross section of the abdomen
• Spine seen on cross section (3 white
spots)
• Stomach bubble (hypoechoic, left side)
• Intrahepatic portion of the umblical vein
• Large sections of the fetal ribs (Unbroken
and equal size)
• Kidneys not visualized

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• Principles
– Obtain a longitudinal view demonstrating
the heart and bladder
– Slide laterally till spine is visualized
– Rotate 90 degree at the level of fetal
stomach
– Sliding movements of the transducer to
visualize the umblical vein
– Freez the image

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• Measuring the AC
– Two diameter method
• APAD
• TAD
–AC = 3.14 (TAD + APAD)/2

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Two diameter method

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54. Hale T., M.D., Resident Physician
• Directly anterior fetal spine
– Umbilical vein will not be seen
• Options
–Dip one end of the transducer
–Slide the transducer to a more lateral
position
–Complete the remainder of the
examination
»Fetus might have moved into a
more favorable position

55. Hale T., M.D., Resident Physician
Appreciate the difference

56. Hale T., M.D., Resident Physician
Avoid measuring the AC if at all possible when
the fetal spine is at 6 or 12 o’clock

57. Hale T., M.D., Resident Physician
• Non-circular outline
– An oval outline indicates an oblique cross-
section
– Slight change in rotation or angle
• Long length of umbilical vein
– Shows oblique and incorrect section

58. Hale T., M.D., Resident Physician
Spine positions at 9 or 3 o’clock are most optimal for AC
measurement as it minimizes shadowing

59. Hale T., M.D., Resident Physician
Spine position at 12 and 6 O'clock position:
Least optimal for AC measurements

60. Hale T., M.D., Resident Physician
• Femural Length
– As accurate as the BPD in the prediction of
gestational age
– Can often be obtained when fetal position
prevents measurement of the BPD or HC
– The femur can be measured from 12 weeks
to term
– Should not replace that of the BPD or HC
as the sole predictor of gestational age

61. Hale T., M.D., Resident Physician
• Femur Length
– Principles
• The whole femur diaphysis should be
displayed on the screen,
• The angle between the insonating beam
and the shaft of the femur should be kept
in the range of 45-90°
• The longest visible diaphysis should be
measured
• Exclude epiphysis
• Exclude triangular spur artefacts that can
falsely extend the diaphysis length

62. Hale T., M.D., Resident Physician
– Measuring the femur is ideally undertaken
after the AC has been measured
– Slide the probe caudally from the AC
section until the iliac bones are visualized
– The upper femur should be selected for
measurement
• The lower femur is frequently difficult to image
clearly because of acoustic shadowing from fetal
structures anterior to it

63. Hale T., M.D., Resident Physician
– Keeping the echo from the anterior femur in
view, rotate the probe slowly until the full
length of the femur is obtained
– To ensure that you have the full length of
the femur and that your section is not
oblique, soft tissue should be visible
beyond both ends of the femur
– Measure from the center of the ‘U’ shape at
each end of the bone

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Growth of the femur with increasing gestational showing
97th, 90th, 50th, 10th and 3rd centiles

68. Hale T., M.D., Resident Physician
• Problems
– Fetal movements
– One or both end-points are difficult to
define
– The upper femur appears straight but the
lower femur appears bowed
– Gestational age equivalents of the BPD or
HC and femur disagree

69. Hale T., M.D., Resident Physician
• Estimating Fetal Weight
– Hadlock et al is the formula that is most
commonly used for EFW
– Calculating the EFW is more accurate in the
second trimester than the third trimester
but EFW is clearly of lesser clinical relevance
in the second trimester
– In the 3rd trimester, EFW is of crucial
importance to detect fetal growth restriction
or macrosomia
– The estimation of macrosomia is not very
accurate and the error can exceed 10%

70. Hale T., M.D., Resident Physician
• Confirming or Assigning Gestational Age
– GA confirmed and EDD set by early pelvic
ultrasound
• Second trimester scans only used for
assessment of fetal growth
– Scan done in the second trimester for the
first time
• Assign GA and set EDD if LNMP uknown
or unreliable
• Measurements used to assess GA
–BPD or HC and the FL

71. Hale T., M.D., Resident Physician
• Confirmation of GA at the 2nd trimester
examination is based either on a reliable
LNMP or/and on measurements from early
scans
– The measurements of the BPD or HC and
the FL fall within the normal range for the
gestational age when plotted on
appropriate charts
– Measurements of the BPD or HC and the FL
fall outside the normal range for menstrual
age

72. Hale T., M.D., Resident Physician
– The BPD or HC falls within normal range for
the known gestational age but the FL is
below the normal range
– The FL falls within the normal range for
known gestational age but the BPD is
below the normal range

73. Hale T., M.D., Resident Physician
• Assigning GA for the first time in the 2nd trimester
(Unknown LNMP, No early scan)
– The gestational ages calculated from both the BPD
or HC and FL dating tables agree to within 7 days
• Confrim GA and Set EDD taking the average
– The gestational ages calculated from the BPD or HC
and the FL dating tables differ by more than 7
days
• BPD and HC agree with AC and TCD
– Take BPD or HC for GA confrimation
– Study the cause of FL abnormality
• FL agree with AC and TCD
– Take FL for GA confirmation
– Study the cause of HC and BPD abnormalities

74. Hale T., M.D., Resident Physician
• Two most popular formulas:
– Shepard formula
• Log10 BW=-1.7492+0.166(BPD)+0.046(AC)- 2.646
[ACxBPD] /100
– Hadlock formula
• Log10BW=1.3598+0.051(AC)+0.1844(FL)-
0.0037(ACxFL)

75. Hale T., M.D., Resident Physician
• Other biometric parameters
– Intra- and interorbital diameters,
– Clavicle length,
– Foot length, and
– Length of long bones of the extremities
– Fetal body ratio indexes (HC/AC, BPD/FL,
FL/AC)

76. Hale T., M.D., Resident Physician
Basic Fetal Anatomy
• List of basic fetal anatomy in the second
trimester of pregnancy
– Head
• Lateral central ventricies
• Choroid plexus
• Midline falx
• Cavum septae pellucidi
• Cerebellum
• Cistern magna
• Upper lip
• Philtrum

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– Chest
• Heart
– 4 chamber view
– Left ventricular outflow tract
– Right ventricular outflow tract
• Lung fields
– Abdomen
• Stomach
• Kidneys
• Urinary bladder
• Umblical cord insertion into the fetal abdomen
• Umblical cord vessel number

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– Skeletal
• Cervical
• Thoracic
• Lumbar
• Sacral spine
• Extremities
– legs and arms
– Placenta
– Aminotic fluid
– Adnexae

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• Ultrasound examination is in the unique
position of being both a screening test
and a diagnostic test for fetal anomalies

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• Optimal time for fetal anomaly scan
– 18-20 weeks?
– 20-22 weeks?
– 23-24 weeks?

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• Head Anatomy
– Three axial sonographic planes are needed
to assess the head anatomy:
• The plane at the level of the lateral ventricles
• The plane at the level of the BPD and
• The plane at the level of the posterior fossa

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Transverse plane of the fetal head at the level of
the lateral ventricles
The LV is measured at the level of the atrium

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Transverse plane of the fetal head at the
level of the Thalami

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Transverse plane of the fetal head at the level of
the posterior fossa

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Transverse section of the fetal head at the level
of the posterior fossa

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Plane at level of Lateral Ventricles
Bilateral Ventriculomegally
V/H > 0.5
VD > 10

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Choroid P cysts Trisomy 18

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Holoprosencephaly:
=> Results from failure of division of the prosencephalon during early
embryogenesis into two lateral ventricles
Holoprosencephaly

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Anencephaly:
Absence of brain tissue associated with absent
calvarium
Anencephaly

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Prominent orbits and absent
calvarium— ’Frog Sign’

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Encephalocele:
Localized defect of cranium – neural tube defect
Encephaloceles

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Cystic hygroma at 24 weeks’ gestation ( ‘cart
wheel’)

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Posterior Fossa

94. Hale T., M.D., Resident Physician
• Complete or partial absence the cerebellar vermis, varying degrees of
hydrocephalus 50% of affected fetuses have other intracranial malformations,
35% extracranial abnormalities and 15-30% have aneuploidy
Cystic Hygroma
Dandy Walker
malformation

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Cerebellar vermis dysgenesis

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Posterior fossa changes (Chiari II)

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Spina bifida Spina bifida

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Bilateral ventriculomegally Bilateral ventriculomegally

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Agenesis of the corpus callosum Septo-optic dysplasia

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Basic sonographic anatomy of the face can be primarily
achieved by the evaluation of the orbits and the upper
lip and philtrum
Tangential plane of the
fetal head at the level of the
orbits
Tangential plane of the
fetal face

101. Hale T., M.D., Resident Physician
Midsagittal view of the fetal head and face

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Tangential view: Important to see cleft palate
Tangential plane of the fetal
face

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• Chest Anatomy
– The plane required to assess both the lungs and
the heart is the 4-chamber view, which corresponds
to an axial view of the chest at the level of the
heart

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Longitudinal section of the fetal body

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Hypoplastic left heart syndrome

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Congenital Diaphragmatic Hernia
1. Cystic mass is
seen in the left
fetal chest
2. No stomach
‘bubble’ visible
in the
abdomen
3. Heart pushed
to the right
side

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Congenital cystic adenomatoid
malformation of the lung

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• Anatomy of the Fetal Abdomen

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• Transverse section of the normal umbilical cord
at 24 weeks demonstrating the presence of two
arteries and one vein

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Transverse section of the fetal abdomen
demonstrating both kidneys and renal
pelves
Transverse section of the fetal
abdomen demonstrating echogenic
bowel

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Duodenal atresia Omphalocele

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Gastroschisis

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Infantile polycystic kidney disease

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Posterior urethral valves

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• The Fetal Limb
– In the view that demonstrates Tibia and Fibula if
the plantar or footprint view of the foot is obtained
in this section, talipes should be suspected

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Talipes
Trisomy 18, 13 and
triploidy

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Sandal Gap
Trisomy 21 and Triploidy

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Rocker-bottom feet
Protruding heel and convex shape of the sole of the foot

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The Spine

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Banana-Shaped

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Lemon-shaped

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Lethal Skeletal Dysplasia

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130. Hale T., M.D., Resident Physician
• Fetal Sex
– Transabdominally
starting from 14
weeks
– Male: Scrotum and
penis identified
• Testis in the
scrotum
– Female: A lip in
between the two legs

131. Hale T., M.D., Resident Physician
• Do not diagnose a female by an
apparent lack of male parts
• Do not ask the parents if they wish to
know the sex of their baby
– Many parents assume that if you have asked
the question the fetus must be a male
• Never guess!

132. Hale T., M.D., Resident Physician
• Summary
– Stepwise approach helps to standardize
scaning process and systemic evaluation
– Optimal time for second trimester scanning
is 18-20 weeks; extending 20-22 weeks adds
the advantage of screening for fetal heart
anatomy
– Understanding to obtain proper sections is
crucial for accurate age and size
determination

133. Hale T., M.D., Resident Physician
REFERENCES

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REFERENCES

135. Hale T., M.D., Resident Physician
Thank you for listening!