Pregnancy Time’s Special Tests
ULTRASOUND
Almost all women are now offered an ultrasound scan. Your
partner may be able to come with you for the scan, and many couples find it
quite fascinating. A full bladder helps to give a clearer picture as it keeps
the baby quite high in the abdomen. Your stomach will be lubricated. And the
scanner passed over it. Sound waves are passed into the uterus to build up a
picture of the baby and the placenta. The picture on the monitor may look
rather indistinct, but usually the person doing the scan can point out where
the head and limbs are. Often the baby’s beating heart shows up quite clearly.
In early pregnancy you can usually make out most of the baby, but later on, as
the baby gets much larger, it is harder to see him all at once.
From a
medical point of view the scan is useful to confirm the date of pregnancy.
Measurements may be take of the spine or head, or the long bones of the thigh.
The scan date is a little more accurate than dating the pregnancy from the
first day of your last period, if your periods are regular.
Ultrasound
scanning is also used to check the development of the baby, to ensure that
any
problems are picked up early. Sometimes these can be dealt with during
pregnancy, and in some hospitals procedures such as clearing a blocked urethra
to relieve pressure on the kidneys can be done at once. Being forewarned of a
problem may mean that the baby will have to be delivered in a tertiary care
hospital.
Scans
can confirm a multiple or twin pregnancy, and show where the placenta is lying
ALPHA-FETOPROTEIN TEST
You will probably have a blood sample taken at around
sixteen weeks to measure the levels of substance called alpha-fetoprotein. If
the levels are higher than expected, it can indicate a problem such as spina
bifida. However, it can also mean that the pregnancy is further along than was
thought, or that there is more than one baby. If AFP levels are high, an
ultrasound scan and/or other tests will be done to establish the cause.
MATERNAL SERUM SCREENING
New types of test recently become available called the
triple screen. These involve taking a blood sample and analyzing if for
specific signs. The result, combine with other factors such as the mother’s
age, can be used to predict the risk of conditions such as Down’s syndrome.
These tests have the advantage that they are non-invasive (see below), but they
are not diagnostic; they cannot tell you if your baby has Down’s syndrome, only
what your risk factor is if the factor is high, you can then can choose to have
a more invasive test like amniocentesis. At the moment tests can throw up false
positive readings and some of the women who are thought to have high risk
actually do not. For them, the test result cause unnecessary worry. For others,
a negative blood test rules out a more invasive test such as amniocentesis or
chorine biopsy (see right). The term `invasive’ refers to the fact that these
tests involve taking samples of amniotic fluid or cells from the placenta and
carry the risk of miscarriage. The extra information supplied by the Triple
screen, which carries no risk, can help parents decide whether to undergo
further tests. Maternal serum screening is not available in all areas, so ask
your doctor about it. The tests are being improved and refined and it is hoped
that the false positive problem will decrease.
AMINOCENTESIS
This involves taking a sample of the amniotic fluid that
surrounds the baby. It is used to check for chromosomal abnormalities such as
Down’s syndrome. As there is a risk of miscarriage after the test, it is only offered
if the chances of Down’s syndrome are considered higher than average. The
incidence of Down’s syndrome increases with the mother’s age, so in some areas
women over thirty-eight of forty are offered the test. It may also be suggested
if one of the diagnostic tests such as the triple screen shows an increased
risk.
An
ultrasound scan is used to show the position of the baby and the placenta, and
then a fine needle is passed through the abdominal wall to draw off some of the
fluid. Most women find the process quite painless, although they are usually
advised to rest for a day or two after the test.
CHORIONIC VILLOS SAMPLING
In this test, a few of the cells of the placenta are taken,
using a fine needle passed through the cervix. It can be done much earlier than
amniocentesis, before eleven weeks of pregnancy, so allowing an earlier
decision to be made regarding termination, if necessary. Unfortunately, the
risk of miscarriage is higher than with amniocentesis, and there is also a risk
of limb deformities. It tends to be used where the need for the information it
can give outweighs the risks.AFTER THE TEST
For many couples the greatest worry come with deciding what
to do if a test prove positive, which means that there may be an abnormality.
Making a decision about continuing a pregnancy, or choosing a termination is
never easy. Some couples feel strongly either for or against, while others feel
unsure, confused and upset. If may help to talk things through with your
midwife or doctor. They will be able to give you more information, refer you to
a geneticist and put you in touch with a local support group where you can
contact couples who have gone through a similar experience, though you may wish
to resolve the issue yourselves.
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