lecturer of obstetric& gynecology
Definition of Ultrasound
Ultrasound means sound waves of frequency
higher than those heard by the human ear.
no definite complications for diagnostic ultrasound
when the frequency used is less than 10 MHz
Ultrasound in diagnostic obstetrics and gynecology is
used in the range between 3-8 MHz
A- In normal pregnancy
The early pregnancy scan
Mid-pregnancy Scan (Anomaly Scan)
Late Pregnancy Scan.
B- In abnormal pregnancy
From 10-13 weeks is best for early
detection of trisomy.
From 5-8 weeks is best for early
detection of ectopic pregnancy.
Trans-vaginal if 5-8 weeks.
Trans-abdominal if 10-13 weeks.
Accurate Evaluation of gestational age
Using crown-rump length (CRL)
accuracy close to +/- 4 days.
Early Detection of Ectopic Pregnancy
Early Exclusion of trisomy 21(congenital
establish the presence of a living
Obstetrical ultrasound is a useful clinical test to:
establish the presence of a living embryo/fetus.
estimate the age of the pregnancy.
diagnose congenital abnormalities of the fetus.
evaluate the position of the fetus.
evaluate the position of the placenta.
determine if there are multiple pregnancies.
determine the amount of amniotic fluid around the
check for opening or shortening of the cervix.
assess fetal growth.
assess fetal well-being.
You should wear a loose-fitting, two-
piece outfit for the examination
Only the lower abdominal area needs to
be exposed during this procedure.
In early pregnancy US, full bladder is
In transvaginal US, empty bladder is
the patient is positioned lying face-up on an
examination table that can be tilted or moved.
A clear water-based gel
help the transducer make secure contact with the body
eliminate air pockets between the transducer and the skin
presses the transducer firmly against the skin in various
sweeps over the area of interest.
angling the sound beam from a farther location to better
see an area of concern.
Transvaginal ultrasound is performed very
much like a gynecologic exam and
involves the insertion of the transducer into
the vagina after the patient empties her
bladder, lying on her back, possibly with her
feet in stirrups.
A protective cover is placed over the
transducer, lubricated with a small amount
of gel, and then inserted into the vagina.
Only two to three inches of the transducer
end are inserted into the vagina
The images are obtained from different
orientations to get the best views of the
uterus and ovaries.
Most ultrasound examinations are painless, fast and
easy, usually no discomfort from pressure.
If scanning is performed over an area of
tenderness, you may feel pressure or minor pain
from the transducer.
With transvaginal scanning, there may be minimal
discomfort as the transducer is moved in the
Once the imaging is complete, the gel will be
wiped off your skin.
Earliest sign of
seen at 4-4.5 weeks
It is intradecidual
Can be used for
A normal gestational
sac grows by 1 mm
its normal eccentric location: it is
embedded in endometrium, rather than
centrally within the uterine cavity
presence of a yolk sac : seen at
approximately 5.5 weeks or with a beta-
HCG of ~7000m IU/ml
presence of the double decidual sign
Seen at 5 weeks
true from pseudo
Seen at 20 mm
8 mm sac
Seen at 6
Should be seen
at sac diameter
Heart beat is
seen at CRL of
Gestational sac – 4 to 5 weeks
Yolk sac – 5 to 6 weeks
Fetal pole - 6 to 7 weeks
Cardiac Activity - 6 to 7 weeks.
Failed early pregnancy refers to the
death of the embryo and
The most common cause of embryonic
death is a chromosomal abnormality.
A pregnancy is considered non-viable on
transvaginal ultrasound if:
no fetal heart beat where:
› CRL ≥ 7 mm
no fetal pole where:
› MSD > 25 mm with no embryo
Both fetus and gestational sac are
expected to grow 1mm/day. Hence,
absence or inadequate growth on serial
scans at least 7-10 days apart
is suggestive of non-viability.
no yolk sac, where:
› MSD > 8 mm
› embryo seen
irregular gestational sac
low position of the gestational sac
Normally BHCG doubles every 48hours
Discrimination zone: relies on BHCG
increasing by >66% in 48 hours, if not and
no considerable bleeding think of
ectopic pregnancy if uterus is empty on
However 5% of normal pregnancies
don’t behave like that
Only seen in 10-20%
Sac is intra-decidual
No yolk sac or fetal
pole at sac
diameter of 25 mm
Sac can be irregular
Low uterine position
If unsure repeat in 1
Very High BHCG
Theca lutein cysts in
The ovaries are commonly the site for theca lutein
cysts secondary to the BHCG.
Gestational sac seen at 4.5 weeks
Yolk sac seen at 5 weeks
CRL seen at 6 weeks with sac diameter
Heat beat seen at CRL of 5mm
If too early or unsure repeat in 1 week
It is essential to accurately date the
pregnancy for adequate timing of
delivery, management of post-maturity
and small for gestational age.
Use LMP if regular periods and certain
dates, then first trimester ultrasound to
Visible form 4.5 weeks
by T.V scan
Implanted on one
side of the uterine
As the sac is not
usually round, an
average of the
length, width and
depth is made.
The accuracy of
dating using GS size is
low and can be off
by a whole week
This is therefore not
Before placental circulation is established, the yolk
sac is the primary source of exchange between
the embryo and the mother.
In a normal early pregnancy, the diameter of the
yolk sac should usually be < 6 mm while its shape
should be near spherical.
As the pregnancy advances, the yolk sac
disappears and is often sonographically not
detectable after 14 weeks
Absence of the YS in the presence of
an embryo is always abnormal and is
associated with fetal demise.
A larger than normal YS is also
associated with adverse outcome in
Visualization of multiple yolk sacs is the
earliest sign of a polyamniotic
pregnancy, e.g. twins.
Measure from top of head
Always measure in neutral
made between 7 to 13
with the CRL can be
within 3-4 days of LMP)
it should not be changed
by a subsequent scan.
• Standard – Anatomic Survey
• Limited – Targeted to answer a question
• Specialized – Targeted anatomic
All can be + or – 2 weeks
either side of the
The diameter between the 2 sides of the
This is measured after 13 weeks.
Dating using the BPD should be done as
early as is feasible.
Different babies of the same weight can
have different head size, therefore dating in
the later part of pregnancy is generally
The BPD remains the standard against
which other parameters of gestational age
assessment are compared
A wrong measurement plane can produce
errors up to 20mm !
The measurement is taken from the
outer edge of the near cranium to the
inner edge of the far cranium.
a middle-to-middle measurement is
The BPD can be smaller (and sometimes
much smaller than is expected) in
fetuses with flatter heads(check the
Same as BPD
On the outer
margin of the bony
More indicative of
serves as a monitor for growth of the long
The femoral shaft is seen as a slightly
curved, echogenic structure that produces
an acoustic shadow
The longest dimension of the femoral shaft is
measured for the FL
The transducer should be aligned along the
long axis of the bone should include
measurement of the entire diaphysis.
The femoral epiphysis, seen as a spike on
one end of the femoral shaft, is not
included in the measurement.
The measurement is most accurate when
the femur is perpendicular to the US beam
Measures the longest bone in the body and
reflects the longitudinal growth of the fetus
The use of FL in dating is similar to the BPD,
and is not superior unless a good plane for
the BPD cannot be obtained or that the
head has an abnormal shape.
Similar to the BPD, dating using the FL
should be done as early as is feasible.
The FL is a mandatory measurement
the FL has a very important function of
excluding dwarfism in the fetus.
The extension to the greater trochanter and
the head of femur should not be included
The measurement is also consider
inaccurate when the femur image is at an
angle of over 30 degrees to the horizontal.
measurement of the FL is considered
accurate only when the image shows
two blunted ends.
Do not take an average of the BPD and FL
for dating, because you can always have a
fetus with an average size head and a
longer or shorter than average lower limb
The measurements should be reported as
they are. Do not take an average.
› U/S beam should be perpendicular to the bone
› Measurement is made along the femur diaphysis
› Exclude the distal femoral diaphysis
o Spine + rib
o Part of portal
o Picture should
be as round as
The single most important measurement
to make in late pregnancy
It reflects more of fetal size and weight
rather than age.
Serial measurements are useful in
monitoring growth of the fetus.
AC measurements should not be used
for dating a fetus.
It is also a mandatory measurement.
The best plane is the one in which the portal
vein is visualized in a tangential section.
The plane in which the stomach is visualized
is also acceptable.
The outer edge of the circumference is
On screen computer-generated elliptical
measurements probably yield the best
Positive cardiac activity
› Absence of cardiac activity for
at least 2-3 minutes
› Ideally confirmed by two or
Lie - relationship of long axis of fetus to
the long axis of the mother
Presentation – part of the fetus closest to
maternal pelvic inlet or cervix
› Cephalic (vertex, sinciput, brow, face)
The earliest time is 12 weeks if in right
Best done between 17-20 weeks
What you will see????
Male: penis or scrotum
Female: The 3-lines sign which denotes
The absence of the penis must not be
taken as sufficient evidence of the fetus
being a girl
MALE:dome shaped genital swelling with a
FEMALE:three or four parallel
lines representing the labia
Inner border of placenta against the uterine wall
has the combined hypoechoic myometrium and
interposed basilar layer = hypoechoic band called
the decidua basalis (contains maternal blood
Outer surface abutting the amniotic fluid =
chorionic plate (chorioamniotic membrane)
= bright specular reflector
Placental thickness judged subjectively
But if measure at mid position or cord insertion 2-4 cm
Placental calcification. Scan of posterior placenta at 39 wks
shows calcification along the basal plate (arrows), chorionic
plate (open arrows), and septa (arrowheads
Midline sagittal scan at 28 weeks shows the posterior
placenta (P) completely covering the cervix (C). B,
the placenta had invaded
through the myometrium to
the bladder wall
Combination of NST with 4 real-time
2 points given to each observation
that is normal or present
Maximum 30 minute time frame.
Each of the 5 components of the
biophysical profile score do not have
equal significance. Fetal breathing
movements, amniotic fluid volume, and
the non-stress test are the most powerful
Components of the 30 minute
Biophysical Profile Score
> 3 body or limb movements
Fetal tone One episode of active extension and
flexion of the limbs; opening and
closing of hand
>1 episode of >30 seconds in 30 minutes
- Hiccups are considered breathing activity.
A single 2 cm x 2 cm pocket is considered
2 accelerations > 15 beats per minute of at least
15 seconds duration.
› NST (short-term indicator of acid/base status)
Considered normal if NST is reactive and AFI
is >5 cm
Positive end diastolic
Absent / Reverse EDF in
Umbilical Artery of
Low resistance can be a sign of redistribution of
blood in the foetus in cases of IUGR
This is the last vessel to be affected in IUGR
and is used to decide timing of delivery.
Measure the dimensions of the largest
vertical pocket of amniotic fluid.
Pocket of fluid
<1cm = oligohydramnios
1-2cm = decreased fluid
2-8cm = normal
>8cm = polyhydramnios
Controversies in cut-off criteria for
› < 0.5 mm
› < 1 cm
› < 2 cm
› < 3 cm
Technique(4 quadrant technique)
Divide the uterus into four quadrants using the
linea nigra as the vertical axis and the
umbilicus as the horizontal axis.
Linear transducer head placed along mother’s
longitudinal axis and held perpendicular to the
floor in the sagittal plane.
The pocket with the largest vertical dimension
is measured in each quadrant.
Sum of all four measurements = AFI
Cord or extremities may traverse the
pocket, but may not be measured as
part of the vertical depth
<5cm = very low (oligohydramnios)
5-8cm = low
8-25cm = normal term AFI
>25cm = polyhydramnios
• Excessive transducer pressure
• Cord-filled pockets should not be used
• Obese patients may introduce scatter
that creates artifact echoes
– May overcome with lower frequency
• Not measuring low in the uterine cavity