2. Obstetrical Ultrasound
• Introduced in the late 1950’s
ultrasonography is a safe, non-
invasive, accurate and cost-effective
means to investigate the fetus
• Computer generated system that uses
sound waves integrated through real
time scanners placed in contact with a
gel medium to the maternal abdomen
• The information from different
reflections are reconstructed to
provide a continuous picture of the
moving fetus on the monitor screen
3. Obstetrical Ultrasound
Indications:
• Unsure last menstrual period
• Vaginal bleeding during pregnancy
• Uterine size not equal to expected for dates
• Use of ovulation-inducing drugs confirm early pregnancy
• Obstetric complications in a prior pregnancy: ectopic, preterm
delivery
• Screen for fetal anomaly: abnormal serum screens, certain drug
exposure in early pregnancy, maternal diabetes.
Rhisoimmunization
• Postdate fetus
• Twins (monochorionic)
• Intrauterine growth restriction (IUGR)
RADIUS study (1993) did not support routine US screening
5. Obstetrical Ultrasound
• Pre and peri-ovulation (1-2 weeks): ovarian
follicle matures and ovulation
• Conceptus (3-5 weeks): Corpus luteum,
fertilization, morula, blastocyst, bilaminar
embryo
• Embryonic (6-10 weeks): Trilaminar C-shaped
embryo
• Fetal Phase: (11-12 weeks):
6. Obstetrical Ultrasound
(TVU)
Gestational sac: seen at 4 weeks, fluid
filled with echogenic border, grow at least
0.6 mm daily.
Yolk sac: 33 days (4.7 wk)
Embryonic echoes: 38 days (5.4 w) with
embryo at 6 wk
In a normal pregnancy, the embryo should
be visible if the gestational sac is 25 mm
or larger in diameter.
7. Obstetrical Ultrasound
• An intrauterine gestational sac should be visualized by
transvaginal ultrasound with β-hCG values between 1000
and 2000 IU and abdominal exam 5500-6500 IU
• Visible heart activity: 43 days (6.1w)
• Normal heart rate at 6 weeks: 90-110 bpm
• At 9 weeks:140-170 bpm.
• At 8-9 weeks if nl heartbeat: no bleeding 3%loss
bleeding 13% loss
• At 5-8 weeks a bradycardia (<90 bpm) is associated with a
high risk of miscarriage.
8. Obstetrical Ultrasound
• CRL(Crown Rump Length):
• Longest length excluding
limbs and yolk sac
• Made between 7 to 13
weeks
• 3 days: 7-10 weeks
• 5 days: 10-14 weeks
• Fetal CRL in centimeters plus
6.5 equals gestational age in
weeks
9. Obstetrical Ultrasound
• Ultrasound findings in a
pregnancy destined to abort
include:
• A poorly-defined, irregular
gestational sac
• A large yolk sac (6 mm or
greater in size)
• Low site of sac location in the
uterus
• Empty gestational sac at 8
weeks' gestational age (the
blighted ovum).
10. Obstetrical Ultrasound
First Trimester Screening
• In 2007, the American College of Ob Gyn endorsed offering
aneuploidy screening to all gravidas
• Performed between 11 and 13 weeks 6 days (fetal crown–
rump length 42–79 mm).
• Fetal nuchal translucency and maternal blood, β-hCG and
pregnancy-associated plasma protein A (PAPP-A).
• This test can detect approximately 60-85% of fetuses with
Down syndrome, with a 5% false positive rate.
• Abnormal screen can increase the risk of genetic, other
aneuploidiesand other cardiac anomalies
11. Obstetrical Ultrasound
Nuchal translucency:
• Translucent space between the back of the
neck and the overlying skin
• The scan is obtained with the fetus in sagittal
section and a neutral position .
• The fetal head (neither hyperflexed nor
extended, either of which can influence the
nuchal translucency thickness).
• The fetal image is enlarged to fill 75% of the
screen, and the maximum thickness is
measured, from leading edge to leading edge.
(inner to inner measurement)
• It is important to distinguish the
nuchallucency from the underlying amnionic
membrane.
• > 6 mm considered abnormal
13. Obstetrical Ultrasound
• Cervical length
• Endovaginal probe, examine in dorsal lithotomy position with
empty bladder
• Normal cervix should have a length of 2.5cm or more from 10
weeks gestation until 36 week
• The width of the cervical canal at the level of the internal os
should be less than 4mm
• Document any evidence of funneling
• Optimal gestational age for cervical length assessment is after
16 to 20 weeks gestation
• Assessment 20-24 weeks best time evaluation PTD
16. Obstetrical Ultrasound
BPD:
• Greatest accuracy between 12-28 weeks
(better>14 wks.)
• The plane for measurement of head
circumference (HC) and bi-parietal diameter
(BPD)must include:
• Cavum septum pellucidum
• Thalamus
• Choroid plexus in the atrium of the lateral
ventricles.
• Measure outer table of the proximal skull to the
inner table of the distal
HC:
• Measure the longest AP length
• (BPD + OFD) X 1.62
17. Obstetrical Ultrasound
Abdominalcircumference
• Determined on transverse view
at the level of thejunction of
the umbilical vein, portal
sinus,and fetal stomach
• Measured from the outer
diameter to outer diameter
• Multiply mean diameter by
3.14
• Assessing fetal
weight/IUGR/macrosomia
18. Obstetrical Ultrasound
Femur Length (FL):
• Aligning the transducer with the lower
end of the fetal spine and rotating
toward the ventral aspect of the fetus
• Can measure from 10 weeks onward
• Measurement origin to distal end of
shaft and shows two blunted ends
• Do not include femoral head or distal
epiphysis
• Femur image is at an angle of less than
30 degrees to the horizontal.
• It increases from about 1.5 cm at 14
weeks to about 7.8 cm at term.
Humerus
• Measured similarly
19. Obstetrical Ultrasound
Amnionitic Fluid
• AFI: measure four quadrants
of largest verticle pocket
• 5-20 cm. nl, 6-8 cm.
borderline,<5 cm
oligohydramnios
• Polyhydramnios is defined as
an amniotic fluid volume in
excess of 2000 mL. A single
pocket of fluid that is 8 cm or
larger
20. Obstetrical Ultrasound
Placenta:
• Determining its upper and lower edges r/o placenta
previa
• With increasing gestational age, the placenta
increases in echogenicity because of increased
fibrosis and calcium content.
• This feature of placental maturation has led to a
grading of placentas from immature (grade 0) to
mature (grade 3).
• Placentolmegaly
Diabetes, fetal hydrops, Rhisoimmunization
• Small placenta:
• Severe IUGR (symmetrical/asymmetrical)
Grade 0
Grade 1
Grade 3
21. Obstetrical Ultrasound
• Abnormal placentas
• Placenta Previa
• found in approximately 5% of
second-trimester scans
• If detected at 15–19 weeks, it
persists in 12% of patients.
• If it is detected at 24–27
weeks, it may persist in up to
50%.
• VasaPrevia:membranous
insertion of cord where
exposed vessels cross internal
os
22. Obstetrical Ultrasound
• Fetal anatomy:
• Head
• Atrium of lateral ventricles
• Choroid plexus assessment
• Cerebellum
• Cisterna magna
• Nuchal fold
23. Obstetrical Ultrasound
• The atrium of lateral
ventricles should be less
than 10mm in diameter
(best measured at the
occipital horn).
• The choroid plexii should
be homogenous.
• Small, and sometimes
multiple, choroid plexus
cysts are a common
finding on high resolution
equipment.
• They are of doubtful
significance as an isolated
finding.
24. Obstetrical Ultrasound
The cerebellar diameter should approximately equal the weeks of gestation.
(Ex: 19weeks=19mm)
Cisterna magna: < 10mm
Nuchal fold: (outer edge of occipital bone to skin surface )
<6mm (between 17-20weeks).
27. Obstetrical Ultrasound
• Fetal Circulation
• Blood from the placenta is carried to the fetus by the
umbilical vein
• About half of this enters the fetal ductusvenosus and is
carried to the inferior vena cava
• The other half enters the liver proper from the inferior
border of the liver.
• The branch of the umbilical vein that supplies the right
lobe of the liver first joins with the portal vein.
• The blood then moves to the right atrium of the heart.
• In the fetus, there is an opening between the right and
left atrium (the foramen ovale), and most of the blood
flows through this hole directly into the left atrium
from the right atrium, thus bypassing pulmonary
circulation.
• The continuation of this blood flow is into the left
ventricle, and from there it is pumped through the
aorta into the body
28. Obstetrical Ultrasound
– Some of the blood entering the
right atrium does not pass
directly to the left atrium
through the foramen ovale, but
enters the right ventricle and is
pumped into the pulmonary
artery.
– In the fetus, there is a
connection between the
pulmonary artery and the
aorta, called the
ductusarteriosus, which directs
most of this blood away from
the lungs
29. Obstetrical Ultrasound
Cardiac Anatomy
• Four-Chamber View of the Heart
• The ultrasound beam is directed
perpendicular to the midchest plane
at the level of the heart.
• These chambers consist of the right
and left atrial and both ventricular
chambers
• Corresponding valves between them
http://www.fetal.com/FetalEcho/04%20Standard.html
30. Obstetrical Ultrasound
• The heart is approximately one-third
the area of the chest, inclined to the
left 45 degrees to the midline.
• The AP midline passes through the
left atrium and the right ventricle
• The midline (AP) and the cardiac axis
(arrowhead on dashed line) intersect
and form the angle shown
• Look for asymmetry in chamber size,
defects in the septum or
displacement of the heart
• Detection rate 60-75% for anomalies
with 4 chamber view, higher with
outflow tracts
31. Obstetrical Ultrasound
• Sweep the transducer beam in a transverse plane from the level
of the four chamber view towards the fetal neck
• Right Outflow Tract Left Outflow Tract
• Right outflow track comes Comes off left ventricle
off right ventricle and bifurcates continues into aortic arch
continues into pulmonary artery and then to descending
aorta
41. Obstetrical Ultrasound
Doppler Ultrasound
• Blood flow characteristics in the fetal blood vessels can be assessed with
Doppler 'flow velocity waveforms‘
• Diminished flow, particularly in the diastolic phase of a pulse cycle is
associated with compromise in the fetus.
• Various ratios of the systolic to diastolic flow are used as a measure of this
compromise.
• The blood vessels commonly interrogated include the umbilical artery, the
aorta, the middle cerebral artery, ductusvenosus (DV) and umbilical vein
(UV)
• Abnormal uterine artery Doppler velocimetry and pre-eclampsia, intra-
uterine growth retardation and adverse pregnancy outcomes.
42. Doppler Ultrasound
• Ductusvenosus leads directly into the vena cava to allows some blood rich
in oxygen and nutrients to be pumped out of the body without passing
through the capillary beds in the kidney.
• Abnormalwaveforms in the ductusvenosus may be key to predicting right
heart failure in the hypoxic fetus and an important indicator of imminent
fetal demise (Kiserud 1991).
• Reversed flow in the ductusvenosus is an ominous sign.
43. Doppler Ultrasound
• The umbilical artery is
evaluated measuring the
blood flow velocity at peak
systole (maximal
contraction of the heart)
and peak diastole
(maximal relaxation of the
heart)
• These values are
computed into different
ratios like S/D or RI
44. Doppler Ultrasound
• Predict fetuses at risk
for anemia or hydrops
especially
Rhalloimmunized
pregnancies
• >1.5 MOM or ratios can
be used
47. Obstetrical Ultrasound
• 4D Ultrasounds that adds the element of
time to the 3D process.
• Offers live images
• Fetal changes like movement, kicking, reach
with hands and facial expressions can be
seen
