Download Ultrasound in obstetrics Dr.Zahraa` Muhmmed Jameel

Ultrasound in obstetrics
Dr.Zahraa’ Muhmmed Jameel
• It uses very high frequency sound waves of between 3.5
(abdominal u/s)and 7.0 (transvaginal u/s)megahertz emitted
from transducer.(Audible sound from 20 to 20000 hertz)
• Transducers can be trans abdominal or transvaginal.
• The probe contain piezoelectric crystals which change
electricity to sounds and then receive sounds reflection and
change it into electricity and displayed on the screen
• Is currently considered to be a safe, accurate, noninvasive
and cost effective procedure. It has progressively become an
indispensible obstetric tool and plays an important role in
the care of every pregnant woman
Transabdominal Ultrasound
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Transabdominal approach :
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Lower frequency, lower resolution image
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Curved linear transducer
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Better visualized with full bladder
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Can see coronal and sagittal views of organs and fetus
Transvaginal Ultrasound
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Higher frequency, higher resolution image
Endocavitory probe
Better visualized with empty bladder
Can see sagittal or coronal view of uterus
If possible attempt trans abdominal before considering
transvaginal to avoid more invasive procedure.
– Useful in:
– Early pregnancy
– Examination of cervix later in pregnancy
– Identifying lower edge of placenta
– In women with significant amount s of abdominal adipose
tissue
The main uses of ultrasonography are in the
following areas:
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The gestational sac can be visualized as early as 4-5 weeks
of gestation
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The yolk sac at about 5 weeks.
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The embryo can be observed and measured by about 56weeks.
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A visible heart beat can be visualized by 6 week
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Confirm the site of the pregnancy is within the cavity of the
uterus
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Ectopic pregnancy is suspected if, +ve preg. test, no GS
within the uterus, adnexal mass with or without fetal pole, or
there is fluid in the pouch of douglas .
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Missed miscarriage: fetus identified with an absent fetal
heart(CRL >6mm + no fetal heart)
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Blighted ovum :empty gestational sac in the absence fetal
development(GS >20mm +no fetal pole)
2. Determination of gestational age and
assessment of fetal size &growth.
• a)The gestational sac measurement 5-6 week of
gestation
• b) The Crown-rump length (CRL) can be made 7-13
weeks+6 days
• c) The Head circumference (HC)from 14-20 week of
gestation
• d) The Biparietal diameter (BPD) after 13 weeks
• e) The Femur length (FL) after 14weeks
• f) The Abdominal circumference (AC) It reflects more of
fetal size and weight rather than age.
• The weight of the fetus at any gestation can also be estimated
with great accuracy using polynomial equations containing
the BPD, FL, and AC.
• Essentially, the earlier the measurement is made, the more
accurate prediction (from early CRL ±5 days is preferred to BPD at
20 weeks ±7 days) & GA cannot be calculated by u/s after 20
weeks B/c larger range of normal values of BPD & HC around the
mean.
• In pregnancies at high risk of FGR, serial measurements are
plotted on the normal reference range.
• Growth pattern help to distinguish b/w symmetrical and
asymmetrical FGR (BPD,AC)
• Large HC compared to small AC in brain sparing effect
(asymmetrical IUGR)
• In diabetic preg, AC is large due to effect of insulin on fetal liver
and fat stores
•
Cessation of growth is ominous sign of placental failure
•
3. Multiple pregnancies.
• Determining the number of fetuses, the chorionicity, fetal
presentations, evidence of growth retardation and fetal anomaly,
the presence of placenta previa, and any suggestion of twin-totwin transfusion.
• Thickness of dividing membrane thin in monochorionic twin &
thick in dichorionic twin
• The optimal GA to determine chorionicity is at 9-10 week
• Later in pregnancy, dichorionicity is determined by identification
of 2 placental masses &2 different sex fetuses
• No septum in monochorionic monoamniotic twin
• Thin septum in monochorionic diamniotic twin Formed by 2
layers of amnion
• Thick septum formed by 2 layers of amnion &2 layers of
chorion
Lambda sign or twin peak sign(dichorionic diamniotic twin)
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5-Placental localization
• At 20 week scans, lower uterine has not yet formed & most low
lying placenta appear to migrate upward as the lower uterine
segment stretches in the late 2nd &3rd trimester
• 5% of women have a low lying placenta at 20 weeks, only 5% of
this group will eventually be shown to have placenta previa
• Transvaginal u/s can be used to define lower edge of placenta if
not seen by abdominal probe
6- Amniotic fluid assessment
rd
• Amount of AF in the uterus is a guide of fetal wellbeing in the 3
trimester
• Oligohydramnios is reduction in AF volume
• Polyhydramnios is increase in AF volume
• 2 ultrasonic measurement approaches give indication of AF
volume these are : MVP &AFI
• The Maximum vertical pool is measured after a general survey of
uterine content (2-8)cm
• The Amniotic fluid index is measured by dividing the uterus into 4
u/s quadrants , a vertical measurement is taken of the deepest
cord free pool in each quadrant and the result are summated
The fetus has a role in the control of the volume of AF. It swallows AF,
absorbs it in the gut & later excretes urine in the amniotic sac
• Congenital abnormalities that impair swallow, for example
anencephaly or oesophagial atresia, will result in increase of .AF
• Congenital abnormalities that result in failure of urine production
or passage, for example renal agenesis & posterior urethral valves,
will result in reduced or absent AF.
• IUGR can be associated with reduced AF b/c of reduced urine
output.
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7- Assessment of fetal wellbeing
• A-Biophysical profile is along (30 minutes) ultrasound scan which
observes fetal behavior, measure AF volume& include a CTG.
• Fetuses spend 30% of their time asleep, during which they are not
active, & do not exhibit breathing movements.
• B-Doppler investigations
• Doppler u/s can be used to assess placental function & identify
evidence of blood flow redistribution in the fetus, which is a sign
of hypoxia
• For umbilical artery give information about placental health and
function
• Pulstality index or resistance index(RI) :a measure of the amount
of diastolic flow to systolic flow
• An infarcted placenta (HT) will have increase resistance to flow(
low RI)
• Absent or reverse diastolic flow in the UA has strong correlation
with fetal distress & IUD
• For fetal vessels (middle cerebral arteries , aorta, IVC & ductus
venosus)
• Increase diastolic flow in MCA in hypoxia
• Increase velocity in MCA in anemia (Rhesus disease, twin-to- twin
transfusion syndrome)
• 8- Measurements of cervical length
• Can be assessed by transvaginal u/s.
9- Other uses:
• Confirmation of IUD
• Confirmation of fetal presentation in uncertain cases
• Diagnosis of uterine & pelvic abnormalities during pregnancy, for
example fibromyomata & ovarian cyst.
• u/s & invasive procedures
• Is used to guide invasive diagnostic procedures such as
amniocenteses, chorionic villous sampling & cordocentesis.
• Is used to guide invasive therapeutic procedures such as insertion
of fetal bladder shunt & chest drain
• Fetoscopy
• Doppler ultrasound and the prediction of
adverse pregnancy outcome
• Uterine arteries Doppler in 20-24 week have been used to predict
preg. Outcome.
• may demonstrate markers of increase resistance to flow including
diastolic notch in the waveform in the early diastole
• This associated with adverse pregnancy outcomes as PE, IUGR &
abruption.
• Summary of the aims of obstetric ultrasound
The early preg. Scan (11-14 weeks)
• To confirm fetal viability
• To provide accurate estimation of GA
• To diagnose multiple gestation, in particular to determine
chorionicity
• To identify markers which indicate an increased risk of fetal
chromosomal abnormality such as down syndrome
• To identify fetuses with gross structural abnormalities
• The 20 week scan(18-22)weeks
• To provide accurate estimation of GA if an early scan has not been
performed
• To carry out a detailed fetal anatomical survey to detect any fetal
structural abnormalities or markers of chromosomal abnormality
• To locate placenta and identify the 5% of women with a low-lying
placenta for a repeat scan at 34 weeks to exclude placenta previa
• To estimate AF
Also in some centers to:
• To perform Doppler u/s examination of maternal uterine arteries
to screen for adverse pregnancy outcome, for example :PE
• To measure cervical length to assess risk of preterm deliveries
• Ultrasound in the third trimester
• To assess fetal growth
• To assess fetal well-being