Basic Sonography Ob Tranx

7/28/2019 Basic Sonography Ob Tranx

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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

Documents

Basic Sonography Ob Tranx