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)
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FIRST TRIMESTER ULTRASOUND
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ROLE OF ULTRASOUND Ultrasound is a valuable diagnostic tool in
assessing the following indications: Unsure of Dates Vaginal
Bleeding Pelvic Pain Exclude an ectopic pregnancy Maternal past
history ( Threatened Miscarriage ) Nuchal Translucency (11-14 weeks
: CRL 45-84mm) EQUIPMENT SELECTION AND TECHNIQUE Use a curvilinear
probe (3.5-6MHZ) with low power to reduce risk of biological
effects. use of doppler should be avoided in the 1st trimester.
Transvaginal probe approx 5-9 MHz
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SCANNING TECHNIQUE PATIENT PREPARATION Confirm presence of
intrauterine gestation, and number Look for bright trophoblastic
reaction around sac. Assess maternal ovaries, adnexae and Pouch Of
Douglas (P.O.D) Cervix = assess if closed and measure length
between internal and external os If multiple pregnancy, confirm
number of foetuses, number of sacs, and number of placentas present
to determine chorionicity. ie
Monochorionic/Monoamnionic(MCMA),Monochorionic/Diamni
onic(MCDA),Dichorionic/Diamnionic(DCDA) Confirm heart beat(s) &
rate with M-Mode only (Use of Colour or Doppler traces is not
recommended in the 1st trimester) Measure CRL to calculate
gestational age and Estimated Date of Delivery(EDD). If too early
to see the foetal pole measure the average sac diameter.
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Items must be examined in 1 st. Trimester (less than 12 weeks)
Gestational sac location / size / shape Yolk sac & Amnion Crown
rumple length (CRL) & Embryo Fetal cardiac activity (heart
beat) Amnionitic fluid Fetal morphology>11 weeks) Cranium Heart
Stomach/Bladder/Cord insertion/presence of limbs, hands and
feet
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GESTATIONAL SAC The gestational sac(GS) is the earliest
sonographic finding in pregnancy. The GS is an echogenic ring
surrounding an anechoic centre. An ectopic pregnancy will appear
the same but it will not be within the endometrial cavity. The GS
is not identifiable until approximately 4 & 1/2 weeks with a
transvaginal scan. The GS grow at least 0.6 mm daily. Gestational
sac: seen at 4 weeks, fluid filled with echogenic border
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YOLK SAC &Amnion The yolk sac appears during the 5th week.
It is the second structure to appear after the GS. It should be
round with an anechoic centre. It should not be calcified or
>5mm from the inner to inner diameter. Yolk sacs larger than 6
mm are usually indicative of an abnormal pregnancy. Failure to
identify (with transvaginal ultrasound) a yolk sac when the
gestational sac has grown to 12 mm is also usually indicative of a
failed pregnancy.
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5 week gestation. Yolk Sac Only seen.The yolk sac will be
visible before a clearly definable embryonic pole. Mean Sac
Diameter measurement is used to determine gestational age before a
Crown Rump length can be clearly measured.The average sac diameter
is determined by measuring the length,width and height then
dividing by 3. a transvaginal approach the gestational sac can be
seen during week 4-5.
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CROWN RUMP LENGTH (CRL) & Embryo CRL(Crown Rump Length):
Longest length excluding limbs and yolk sac Made between 7 to 13
weeks Fetal CRL in centimeters plus 6.5 equals gestational age in
weeks
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HEART BEAT An intrauterine gestational sac should be visualized
by transvaginal ultrasound with -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.
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The very early embryonic heart measured using M- Mode The Crown
Rump Length (CRL) measurement in a 6 week gestation.
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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 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) > 6 mm considered abnormal
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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).
2nd TRIMESTER ULTRASOUND PROTOCOL ROLE OF ULTRASOUND In the 2nd
trimester, ultrasound is essential for assessing the Current
viability Structural integrity of the foetus Placental position and
condition This scan must not be done before 18weeks. 19weeks is
optimal. EQUIPMENT SELECTION AND TECHNIQUE Warm gel, clean towels
Use a curvilinear probe (3.5-6MHZ) with low power to reduce RISK of
bio effects.
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SCANNING TECHNIQUE PATIENT PREPARATION Ensure the patient
presents with a full bladder. This will aid in the cervical
measurement and placental position and measurement in relation to
the cervix. Start from the cervix then placenta then baby head,
heart, abdomen, limbs and spine as a rough guide Have your
worksheet with you and mark off as you go so you will not forget
anything.
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WHAT TO CHECK WHEN BABY IS SUPINE Profile,nasal bone,
nose/lips, mandible, palate, orbits. Humerus, rad/ulna, hands,
fingers Heart,4chamber & heart beat Chest cavity Cord
insertion,2 umblical arteries Bladder, gender WHEN BABY IS
DECUBITUS Head, BPD, HC Heart Diaphragm, liver, GB, bowel AC
measurement, stomach, umbilical vein, Spine coronal, trans FL,
femora, tib/fib, feet WHEN BABY IS LYING PRONE Spine Kidneys
Diaphragm Head, choroids
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Transvaginal probe Full bladder Cervical Length: internal os to
external os Cervical length
Slide 20
Biparietal Diameter and Head Circumference (BPD AND HC): BPD:
The plane for measurement of head circumference (HC) and
bi-parietal diameter (BPD)must include: 1. Cavum septum pellucidum
2. Thalamus 3. 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
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Abdominal circumference Determined on transverse view atthe
level of the junction of the umbilical vein, portal sinus,and fetal
stomach NO KIDNEYS in the view Assessing fetal
weight/IUGR/macrosomia
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Femur Length (FL): Aligning the transducer with the lower end
of the fetal spine and rotating toward the ventral aspect of the
fetus Measurement origin to distal end of shaft and shows two
blunted ends Do not include femoral head or distal epiphysis It
increases from about 1.5 cm at 14 weeks to about 7.8 cm at term.
Humerus Measured similarly
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Amnionitic Fluid AFI: measure four quadrants of largest
verticle pocket normal, 6-8 cm. borderline,
3rd trimester ultrasound>26 WEEKS
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3rd Trimester Ultrasound - Protocol Role of Ultrasound
Ultrasound is a valuable diagnostic tool in assessing the following
indications: Follow up of previously identified, or suspected,
abnormality. Suspected or known low placental position Bleeding,
fluid loss or pain Altered maternal health (eg hypertension or
proteinuria) Decreased foetal movements Small for dates (SFD)or
Small for Gestational Age (SGA) or Large for dates (LFD) or Large
for Gestational Age (LGA) Patient Preparation The patient does not
need to drink a lot of water at this stage.
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Scanning Technique Cervix - assess if closed and measure length
between internal and external os Assess placental location and
distance from internal os. Check for retroplacental haemorrhages,
placental masses etc Maternal adnexae (if indicated, also maternal
kidneys) Confirm heart beat & rate Foetal lie: ( eg cephalic,
spine to maternal left) If breech, describe the 'type' of breech.
Frank Complete Footling Head: Shape Symmetry/falx Cerebellum Cavum
septum pellucidum Ventricles
Slide 39
Slide 40
Chest: Heart~ rate (check for arrhythmia) position &
orientation (4 chambers, outflow tracts) Diaphragm Lungs
(homogenous & echogenic relative to liver) Abdo stomach kidneys
bladder anterior abdo wall & cord insertion Limbs: 12 long
bones Position of hands/feet Movement & tone Spine: Symmetry
from C spine to the sacral taper and an intact posterior skin
edge
Slide 41
BIOPHYSICAL PROFILE ASSESSMENT (For utero-placental vascular
insufficiency) Look for foetal movements such as leg, hand flexing
and diaphragmatic movements. Assess foetal tone and posture.
Biophysical Score is a combination of the following assessments
giving them a mark out of 8 in total. Foetal breathing 2/2 Foetal
limb/body movements 2/2 Foetal posture 2/2 AFI 2/2 If the score is
below 7 then this is a concern which will need close follow up. The
assessment must span a minimum of a 30minute period before a
negative report is suggested.
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Obstetrical Ultrasound Three-Dimensional Ultrasound3D Display
multiple longitudinal, transverse, and coronal images. Images may
improve the accuracy of anomaly detection of the fetal face, ears,
and distal extremities
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Obstetrical Ultrasound Abnormal 3D Images Cleft lip
Cyclopia
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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
