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SUBJECT: OB GYNE
Transcriber:Jorge
TOPIC: BASIC SONOGRAPHY IN OBSTETRICS Editor: Aby
Lecturer: Dr. Rex Poblete Number of Pages:7
Sonography in Obstetrics
- The real time image on the ultrasound screen isproduced by sound waves reflescted back from
the organs, fluids, and tissue interfaces of the
fetus within the uterus.
- Transducers convert electrical energy into soundwaves that are emitted in synchronized pulses,
then listen for the returning echoes.
- Because air is a poor transmitter of highfrequency sound waves, soluble gel is applied to
the skin to act as a coupling agent.
- Sound waves pass through layers of tissue, withdifferent densities, and are reflected back to the
transducer.
- Dense tisseu (bone)- bright / white- Fluid dark/ anechoic- High frequency transducers yield better image
resolution
- Low frequency penetrate tissue more effectivelyThe lower the frequency, the more penetration, but it will
compromise the resolution.
So during 1st term, nung maliit pa yung fetus,
transvaginal ultrasoundung gamit. Since malapit ung
probe sa mismong fetus, pwdeng gumamit ng high
frequency (4-9 megahertz), kaya nagiging high din ung
resolution = malinaw ung picture
However, pagdating the 2nd term onwards, since di na
pwde transvaginal ung ultrasound (occupied na ni baby
ung uterus), sa surface ng abdomen na lang ung probe
(which means more tissue in between the probe n fetus).So to get through the tissues (to increase penetration),
kailangan mababa ung frequency (2nd T: 4-6mgHz, 3rd T:
2-5mgHz). But this will compromise the image quality.
Kaya according to doc, minsan magtataka ung mothers
bakit pag first trimester ultrasound and linaw ng picture,
pero pag second trimester na lumalabo.
Anembyonic blighted
- The patient 100% pregnant and intrauterine butno fetus in the gestational sac
- Eventually leads to collapsed gestational sacIst trimester ultrasound
- For the 1st trimester ultrasound is done to checkfor the viability of the fetus and to see if there are
any abnormalities in the uterus and adnexal
structures such as ovarian mass (most common:
corpus luteum), myoma, etc.
- But the primary indicator of viability is the fetalheart tone for the 1
st 10 weeks.
Indications for First Trimester Ultrasound:
Confirm an intrauterine pregnancy Evaluate a suspected ectopic pregnancy Define cause of vaginal bleeding Evaluate pelvic pain Estimation of gestational age Diagnose multifetal gestations Confirm cardiac activity Assist chorionic villous sampling, embryo transfer
and localization and removal of IUD
Assess for fetal anomalies Evaluate maternal pelvic masses/ uterine
abnormalities
Measure nuchal translucency Evaluate suspected gestational trophoblastic
disease
Gestational sac is seen by 5 weeks, and fetal echoes and
cardiac activity by 6 weeks.
Crown Rump length is the most accurate biometric
predictor of gestational age.
Embryonic demise
- If no fetal activity in real time ultrasound, it is anindicator of early intrauterine embryonic demise
Subchorionic hemorrhage
- The detachment of the placenta from the site ofimplantation
- A common finding in patients with vaginalbleeding/spotting and it is an indicator of an
abortion
Nuchal translucency (NT)
First introduced in 1992 as a screening fot fetalchromosome abnormalities
Combined with the maternal age to provideeffective method of screening for trisomy 21
It is measured in the sagittal plane between 11and 14 weeks using precise criteria
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Components of SECOND and THIRD TRI Standard UltrasoundExamination
1. Fetal number; multifetal gestations: amnionicity, chorionicity, fetalsizes, amnionic fluid volume, and fetal genitalia, if visualized
2. Presentation
3. Fetal cardiac activity
4. Placental location and its relationship to the internal cervical os
5. Amnionic fluid volume
6. Gestational age
7. Fetal weight
8. Evaluation of the uterus, adnexa, and cervix
9. Fetal anatomical survey, including documentation of technicallimitations
Increased NT also assess risk for otherchromosomal conditions with associated cardiac
and skeletal abnormalities
Measure the area b/w skin and subQ tissue,>3mm = abnormal
Pathophysiology of NT
1. Cardiac failure in association withabnormalities of the heart and great arteries
2. Venous congestion in the head and neck, dueto constriction of the fetal body in amnion
rupture sequence or superior mediastinal
compression in diaphragmatic hernia or the
narrow chest skeletal dysplasia
3. Altered composition of the extracellularmatrix
4. Abnormal or delayed development of thelymphatics
5. Failure of the lymphatic drainage due toimpaired fetal movement in various
neuromuscular disorder
6. Fetal anemia or hypoproteinemia7. Congenital infection, acting through anemia
or cardiac dysfunction
*Basically NT pertains to the problem mostly
regarding the circulation whether venous, arterial
or lkymphatics.
NT - Nuchal Translucency
Screening is done at 11 to 14 weeks Cut-off value is 3 mm
The nuchal translucency (NT) measurement is the
maximum thickness of the subcutaneous translucent area
between the skin and soft tissue overlying the fetal spine
at the back of the neck. Calipers are placed on the inner
borders of the nuchal space, at its widest portion,
perpendicular to the long axis of the fetus. In this normal
fetus at 12 weeks' gestation, the measurement is 0.9 mm.
Basic ultrasound in second and third trimester
14 weeks up to 42 weeks
1. Indications for second trimester ultrasound2. Components of second trimester3. Biophysical profile
Three types of sonographic evaluations during the
Second- and Third-Trimester Evaluations Its components
are listed in this slide including a survey of fetal anatomy,
When multifetal gestations are studied, documentation
includes the number(s) of chorions and amnions,
comparison of fetal sizes, estimation of amnionic fluid
volume in each sac, and description of fetal genitalia if
visualized. Fetal anatomy may be adequately assessedafter approximately 18 weeks. If a complete survey of
fetal anatomy cannot be obtainedfor example, due to
oligohydramnios, fetal position, or maternal obesitythe
limitation should be noted in the report
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Placenta grading (Grannum)
0 = smooth chorionic plate on the fetal surface
of the placenta w/o calcification
I = placenta with scattered bright echoes
II = increased basal and comma-like
echogenicities extending into the placenta
from the indentations of the chorionic plate
III = Extensive basal, curvilinear echogenecities
extending from the chorionic plate to the
base of the placenta
Amniotic Fluid Assesment
AF plays an important role on assessing fetal growth,
development and status
Abnormal volume
Can interfere with fetal structural development can signify an underlying disorder
AF appearance
Can determine fetal hypoxia (meconium staining)
Sonographic Criteria
1. Subjective assessment2. Single- pocket assessment (SVP)
o For multiple gestation, cannot measurewith umbilical cord
o Oligohydramnios = less than 2 cmo Polyhydrmanios = more than 8 cm
3. Amniotic fluid index (AFI)o Most commono Oligohydramnios = less than 5 cm ( 97.5th percentile)
Oligohydramnios
AFV= < 500cc
= AFI is below 5cm
= SVP is below 2cm
= below the 10th percentile for age
Etiology:
- 2nd to a low fetal urine outout- Anatomic defects- potters syndrome, agenesis,
PUV
- IUGR and placental insufficiency
What is Polyhydramnios?
AFV = 2 liters
= AFI is above 24 cm
= SVP is above 8 cm
= AFI > 90th percentile for age
Etiology:
Maternal in 20%
Fetal in 20% Idiopathic 60%
Implication of polyhydramnios:
Scan for anomalies of fetal upper GIT, CNS, andabdominal wall
Treatment:
1. Amnioreduction/Amniocentesis2. Oral indomethacin
FETAL BIOMETRYUltrasound parameters for fetal aging
1. Biparietal Diameter (BPD) The BPD is measured from the outer edge
of the proximal skull to the inner edge of
the distal skull, at the level of the thalami
and cavum septum pellucidum
more reliable when there is head shapechange
2. Head Circumference (HC) The head circumference (HC) also is
measured. If the head shape is
flatteneddolichocephaly, or rounded
brachycephaly, the HC is more reliable
than the BPD.
Cephalic Index (CI) = BPD/OFD x 100 Dolichocephaly (flattened) = < 74 Brachycephaly (rounded) = > 83
3. Abdominal Circumference (AC) Has the largest reported variability Most difficult to obtain Accurate single predictor of growth
disturbance
Useful in calculating fetal weight The abdominal circumference (AC) has
the widest variation, up to 2 to 3 weeks,
because it involves soft tissue. This
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circumference is most affected by fetal
growth. The AC is measured at the skin
line in a transverse view of the fetus at
the level of the fetal stomach and
umbilical vein
4. Femur Length (FL) The femur length (FL) correlates well withboth BPD and gestational age. It is
measured with the beam perpendicular
to the long axis of the shaft, excluding the
epiphysis, and has a variation of 7 to 11
days in the second trimester
Easiest and most reproducible to
measure
The femur length (FL) correlates well withboth BPD and gestational age.
Measured with the beam perpendicularto the long axis of the shaft, excluding the
epiphysis, and has a variation of 7 to 11
days in the second trimester
Key points in Biometry
The variability of gestational age estimationincreases with advancing pregnancy.
Individual measurements are least accurate in thethird trimester
Estimates are improved by averaging the fourparameters.
If one parameter differs significantly from theothers, it may be excluded from the calculation.
The outlier could result from poor visibility, but itcould also indicate a fetal abnormality or growth
problem.
Sonography performed to evaluate fetal growthshould typically be performed at least 2 to 4
weeks apart (ACOG, 2009; AIUM, 2007)
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Ultrasound Features of Common High Risk OB Cases
Molar pregnancy (H-mole) Placenta previa (Transvaginal Ultrasound more
sensitive in the diagnosis)
Abruptio placenta Preterm labor - Cervical funneling
Preterm Labor
TVS can be used to assess cervical status
Thank Your Vaginal Ultrasound
Determines the shape, length, and degree of shortening
Shape of the Cervix
A T-shaped configuration of the internal os areawith a diameter < 4 mms denotes cervical
competence.
Loss of the normal T-shape to either a Y, V orU shape denotes varying degrees of cervical
incompetence.
Length of the Cervix
A cervical length of 25 mm or less at 24-28 weeks
gestation was significantly associated with preterm births
at < 35 weeks of gestation.
Percentage funneling = A / A+B
Cervical Length RR (95% CI) of delivery
mms (%) at < 35 weeks AOG
24 weeks 28 weeks
22 ( 5) 9.49 13.88
26 (10) 6.19 9.57
30 (25) 3.79 5.39
35 (50) 2.35 3.52
Doppler Velocimetry in Obstetrics
The use of Doppler in obstetrics has beenprimarily in the areas of duplex velocimetry and
color mapping.
The Doppler shift is a phenomenon that occurswhen a source of light or sound waves is moving
relative to an observer and is detected by theobserver as a shift in the wave frequency. When
sound waves strike a moving target, the
frequency of the sound waves reflected back is
shifted proportionate to the velocity and
direction of the moving target. Because the
magnitude and direction of the frequency shift
depend on the relative motion of the moving
target, the velocity and direction of the target can
be determined.
Currently used to evaluate the fetus, placenta, umbilical
cord, and uterine structures
Significance:
1. Prediction of pregnancy-induced hypertensionand IUGR
2. Assessment of fetal status in pregnanciescomplicated by diabetes, isoimmunization, fetal
anomalies and multifetal pregnancies.
Doppler systolicdiastolic waveform indices of blood flow
velocity. The mean is calculated from computer-digitized
waveforms. (D = diastole; S = systole.)
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Blood vessels used for investigation
Umbilical artery Uterine arteries Middle cerebral artery Ductus venosus
Doppler waveforms from normal pregnancy. Shownclockwise are normal waveforms from the maternal
arcuate, uterine, and external iliac arteries, and from the
fetal umbilical artery and descending aorta. Reversed
end-diastolic flow velocity is apparent in the external iliac
artery, whereas continuous diastolic flow characterizes
the uterine and arcuate vessels. Finally, note the greatly
diminished end-diastolic flow in the fetal descending
aorta.
Umbilical artery Normally, with forward flow throughout cardiac
cycle, the amount of flow during diastole
increases as gestation advances
S/D ratio decreases, from about 4.0 at 20 weeksto 2.0 at term
S/D ratio is generally less than 3.0 after 30 weeks Considered abnormal if S/D ratio is above the
95th% for gestational age
useful adjunct in the management of pregnanciescomplicated by fetal-growth restriction
not recommended for screening of low-riskpregnancies or for complications other than
growth restriction.
Normal:
Absent diastolic flow:
Reversed diastolic flow:
Significance!
considered abnormal if the S/D ratio is above the95th percentile for gestational age.
In extreme cases of growth restriction, end-diastolic flow may become absent or even
reversed(ARED) - almost half of cases are due tofetal aneuploidy or a major anomaly
In the absence of a reversible maternalcomplication or a fetal anomaly, reversed end-
diastolic flow suggests severe fetal circulatory
compromise and usually prompts immediate
delivery
fetuses of preeclamptic women who had absentor reversed end-diastolic flow were more likely to
have hypoglycemia and polycythemia (Sezik
and colleagues, 2004)
Uterine artery
Typical - steep sytolic slope, an early diastolic notch, and
a small amount of diastolic flow
Starting at 14 weeks, disappearance of of notchand an increase of diastolic flow - fall in
resistance index
By 20 weeks, 15% retain a notch By 24 weeks, 5% have persistent notch Uterine FVW returns to nonpregnant state within
days after delivery
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Significance!
Failure of the uterine artery to modify (persistence of
diastolic notch) implies that the placentation is defective,
leading to the possible development of problems
associated with poor placentation like pre-eclampsia,
abruption, and IUGR
Timing of investigation?
Increased impedance of uterine artery velocimetry at 16
to 20 weeks was predictive of superimposed
preeclampsia developing in women with CHVD
Middle cerebral artery
studied and employed clinically for detection offetal anemia and in the assessment of growth
restriction
With fetal anemia = peak systolic velocity is increased due to
increased cardiac output and decreased
blood viscosity (Segata and Mari, 2004)
Mari and colleagues (1995) performedMCA velocity studies in 135 normal
fetuses and 39 with alloimmunization.
They showed that anemic fetuses had a
peak systolic velocity above the normal
mean.
Mari and colleagues (2000) used athreshold of 1.50 multiple of the median
(MoM) for peak systolic velocity to
correctly identify all fetuses with
moderate or severe anemia. The false-
positive rate was 12 percent.
In assessment of growth restriction= first is increased impedance of flow in the
umbilical artery followed by
redistribution of flow to the brain, with
decreasing resistance that has been
termed brain sparing, eventually by
abnormalities in venous flow.
At this time, MCA Doppler has notbeenadopted as standard practice in the
management of growth restriction, and
its utility in the timing of delivery of such
fetuses is uncertain.
Ductus venosus
In the setting of severe fetal-growth restriction,cardiac dysfunction may lead to venous flow
abnormalities, including pulsatile flow in the
umbilical vein and abnormal ductus venosus
waveforms
(Reddy and associates,2008)
Ductus venosus abnormalities may identifypreterm growth-restricted fetuses that are atgreatest risk for adverse outcomes
3D Ultrasound
Clinical application:
Morphology, malformation, agenesis (3D, easierin 4D)
Bone shape abnormalities: spina bifida, dwarfism,club feet on one image, cleft palate vs. cleft lip
Skeletal dysplasia abnormalities in dynamic 4D;investigation of spine
Frontal bones, spatial view of fusion or not Variety of fetal volume evaluation: bladder,
stomach, cyst
Fetal well-being (4D): normal vs abnormalgestures; evaluation of fetal sleep vs. awakening.
Motion: deglutition, respiratory motion, eyelid,limbs and mouth motion, fetal digestive
peristaltic motion
Fetal neuro-myopathy genetic disease (4D): fetalreactivity/tonicity
Fetal biopsy (4D): umbilical blood samplingpuncture with precision, amniocentesis, kidney
dilatation, uropathy
Fetal heart (4D): better correlation betweenvalves, chambers and vessels; volume calculation
of heart cavities; atrial and ventricular
communication; assessment of valvular function
Cord insertion using power-Doppler and 3DReferences:
Williams 23rd Edition, chapter 16 Docs ppt
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