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Sonography
(Ultrasound)
A sonography is a procedure that
can be used to evaluate the fetus, placenta and amniotic fluid during a
pregnancy. It is performed using an instrument called a scanner that works
on the echo principle. The machine sends out sound waves that are reflected
back from the surfaces that it scans. These echoes or reflected sound waves
form black-and-white images on a screen, similar to an X-ray.
The sonography is a painless procedure.
The doctor will request you to drink a lot of fluid so that the procedure
can be performed on a full bladder. This enables the doctor to get a clearer
picture. It is a painless procedure save for the discomfort of a full bladder.
In the abdominal technique, the doctor coats the woman's abdomen with mineral
oil or aqua gel and runs the hand-held scanner over her belly. Sometimes
a vaginal probe can be performed early in the pregnancy that involves the
insertion of a vaginal probe. The woman's body is exposed to sound waves
for a fraction of a second. This procedure is not known to have any harmful
effects.
If a woman is bleeding in early pregnancy
(6-12 weeks), a sonography can be performed to detect fetal movement. If
there is no sign of movement, it could indicate a miscarriage. A sonography
can also identify ovarian cysts and ectopic pregnancy as the cause of pelvic
pain in early pregnancy.
Chorionic villus sampling is a procedure
that is performed for some women around 9-11 weeks into the pregnancy to
determine whether the fetus has any birth defects. In these cases, a sonogram
comes in handy to determine the site of the placenta from where the tissue
sample should be obtained. Some women have an amniocentesis approximately
11-18 weeks into their pregnancy to screen for genetic defects. Again a
sonography is helpful as it helps the doctor identify the amniotic fluid
as well as the position of the placenta and fetus that have to be avoided
by the needle.
If the mother has had a child earlier
with a birth defect like anencephaly, spina bifida or hydrocephaly, a sonography
performed between 14-25 weeks of pregnancy could detect these abnormalities.
In the case of high-risk pregnancies
where the doctor might need to induce labour or do a cesarean section,
a sonography performed at 16-25 weeks of pregnancy enables the doctor to
measure the size of the fetus' head and calculate the gestational age and
due date of the baby. A sonography which is done at 16-25 weeks can also
detect if the mother is going to have twins, especially if the fetus seems
to be inordinately big or there is a history of twins in the family.
Sonographies are normally also done
late in the pregnancy (32-40 weeks) for high-risk pregnancies. This is
to monitor fetal movement and respiration and check the volume of amniotic
fluid.
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