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What are Obstetric Ultrasound Scans?
Obstetric Ultrasound is the use of ultrasound scans in pregnancy.
Since its
introduction in the late 1950’s ultrasonography has
become a very useful diagnostic tool in Obstetrics.
Currently used equipments are known as
real-time scanners, with which a continuous picture of the
moving fetus can be depicted on a monitor screen. Very high
frequency sound waves of between 3.5 to 7.0 megahertz (i.e. 3.5 to 7
million cycles per second) are generally used for this purpose.
The main use of ultrasonography are in the following areas:
Diagnosis
and confirmation of early pregnancy.
The
gestational sac can be visualized as early as four and a half
weeks of gestation and the yolk
sac at about five weeks. The embryo can be observed and measured
by about five and a half weeks. Ultrasound can also very importantly
confirm the site of the pregnancy is within the cavity of the
uterus.
Vaginal bleeding in early pregnancy.
The viability of
the fetus can be documented in the presence of vaginal bleeding in
early pregnancy. A visible heartbeat could be seen and detectable by
pulsed doppler ultrasound by about 6 weeks and is usually clearly
depictable by 7 weeks. If this is observed, the probability of a
continued pregnancy is better than 95 percent. Missed abortions and
blighted ovum will usually give typical pictures of a deformed
gestational sac and absence of fetal poles or heart beat.
Fetal heart rate tends to vary with gestational age in the very
early parts of pregnancy. Normal heart rate at 6 weeks is around
90-110 beats per minute (bpm) and at 9 weeks is 140-170 bpm. At 5-8
weeks a bradycardia (less than 90 bpm) is associated with a high
risk of miscarriage.
Multiple pregnancies
In this situation, ultrasonography is invaluable in 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-to-twin transfusion.
3-D and 4-D Ultrasound
3-D
ultrasound can furnish us with a 3 dimensional image of what we are
scanning. The transducer takes a series of images, thin slices, of
the subject, and the computer processes these images and presents
them as a 3 dimensional image. Using computer controls, the operator
can obtain views that might not be available using ordinary 2-D
ultrasound scan. 3-dimensional ultrasound is quickly moving out of
the research and development stages and is now widely employed in a
clinical setting. It too, is very much in the News. Faster and more
advanced commercial models are coming into the market. The scans
requires special probes and software to accumulate and render the
images, and the rendering time has been reduced from minutes to
fractions of a seconds.
More recently, 4-D or dynamic 3-D
scanners are in the market and the attraction of being able to look
at the face and movements of your baby before birth was also
enthusiastically reported in parenting and health magazines. This is
thought to have an important catalytic effect for mothers to bond to
their babies before birth. What are known as 're-assurance scans'
and the rather misnamed 'entertainment scans' have quickly become
popular.
GYNECOLOGICAL ULTRASOUND
For gynecology patients,
ultrasound is used to view internal organs including the uterus,
ovaries, kidneys, and bladder and to scan for cysts and tumors. It
is also used for guidance during biopsies.
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