NBT002206 Diagnostic testing in pregnancy.qxd:12pp 27/05/2010 10:37 Page 2
Diagnostic testing
in pregnancy
Exceptional healthcare, personally delivered
NBT002206 Diagnostic testing in pregnancy.qxd:12pp 27/05/2010 10:37 Page 2
Diagnostic testing in pregnancy
Chorionic Villus Sampling (CVS)
What is CVS?
This is when a small piece of tissue is taken from the placenta.
The placenta contains the same genetic information as the
baby. The cells from the placental tissue are grown and studied in
order to detect some chromosomal abnormalities, for example
Down’s Syndrome.
The most common reason for having a CVS:
■
Prior tests which show you to be at an increased risk of a
chromosome problem.
■
A history of chromosome problems.
■
A history of genetic disorder.
The advantages and disadvantages will be discussed with
you and your partner so that you can decide if this test is
right for you. Whatever you decide, we will support your
decision. Before having any test it is important to consider
how you might feel should the result come back abnormal.
How and when is a CVS performed?
A CVS can be performed from around 11-14 weeks of pregnancy.
You will have a detailed ultrasound scan (USS), and counselling.
The test itself takes a few minutes.
An experienced doctor using ultrasound (scan) guidance
performs the test. You will be given some local anaesthetic
before a fine needle is passed through your abdomen (tummy)
into your uterus (womb), and into the placenta. Women
describe this as being uncomfortable, but not painful. Small
fragments of placenta are withdrawn using a syringe. The
placenta will naturally repair itself.
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Sometimes it is not possible to reach the placenta. If this is the
case you may be asked to return the following week to have
the test done when the placenta and/or the baby may be in a
position that will make it easier to do the test. Alternatively an
amniocentesis will be offered.
Once the test is complete, you will be asked to rest in the clinic
for about 20 minutes before going home. You should bring
someone with you to support you and to drive you home. We
advise that you rest for the remainder of the day and if you are
working, you may need to take the following day off work.
If your blood group has shown you to be rhesus negative, you
will need to be given an injection of anti-d immunoglobulin
following the procedure.
What are the risks?
Every care is taken to reduce the risks to yourself and your
baby. As the test is performed with scanning and involves the
placenta, the risk of damage to your baby is small.
The procedure (test) itself carries a miscarriage risk of 1 in100
(RCOG)* above the risk of natural miscarriage. The test is
performed at a time when there is still a risk of natural
miscarriage occurring, and the earlier the test is performed,
the greater the risk.
You should seek the advice of your community midwife
or your own Doctor (GP) if…
■
You have any vaginal bleeding, or experience an increase in
vaginal discharge.
■
You experience increasing abdominal pain. It is usual to
experience some discomfort following the test. It is safe to
take mild painkillers (paracetamol) to keep you comfortable.
■
If you feel generally unwell or if you have a raised
temperature, as this may indicate infection. A sterile
technique is used, so the risk of infection is small.
These symptoms do not necessarily indicate that you will miscarry,
but it is reassuring to be checked.
Diagnostic testing in pregnancy
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Is it an accurate test?
Because the placenta is a rapidly growing organ, it will occasionally
produce a result that is difficult to interpret. This may mean that
we will need to discuss and offer you an amniocentesis test to
clarify the result, although this is rare.
Occasionally only a small sample is obtained and the laboratory
may not be able to perform the test. Rarely, this may mean
repeating the test.
This is a reliable test for Down’s Syndrome and for some
other chromosome problems. It is not possible to detect all
genetic problems.
The test can reliably tell you the sex of your baby. Please tell
us if you want to know this information.
When do I get the result?
The result comes in two parts:
Part one: This result is usually available in about 3 working
days. This part of the test can only tell us about chromosomes
13, 18 and 21.
Part two: The confirmatory (final) result is available after
about two weeks. This tells us about all the chromosomes.
We will arrange with you how you would like to receive the result.
Once we have received the confirmatory (final) report, we
will send you a letter for a normal result, but will contact you
by telephone if a problem has been identified (shown).
In the event of an abnormal result, you will be offered an
appointment to come back to the antenatal clinic for a
discussion about what to do next, and to help you to make
decisions about how you would like to manage your pregnancy.
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Amniocentesis
What is amniocentesis?
Amniocentesis is the removal of a small amount of the amniotic
fluid (waters) surrounding your baby during pregnancy. This
fluid is usually clear and pale yellow. It contains some of the
baby’s cells. These are grown in the laboratory so chromosomes
can be studied. In this way chromosome abnormalities can be
detected, for example Down’s Syndrome.
The most common reason for having an amniocentesis is an
increased chance of Down’s Syndrome based on prior tests.
It may also be performed when there is:
■
A history of chromosome problems.
■
A history of a genetic disorder.
The advantages and disadvantages will be discussed with
you and your partner so that you can decide if this test
is right for you. Whatever you decide, we will support
your decision. Before having any test it is important
to consider how you might feel should the result come
back abnormal.
When and how is amniocentesis done?
Amniocentesis is performed from around 15-16 weeks of
pregnancy in the antenatal clinic as an outpatient. Bring
someone with you to support you. You will have a detailed
ultrasound scan (USS) and the position of the baby and the
placenta will be checked.
The test itself takes a few minutes and is performed under
ultrasound scan guidance by an experienced doctor, assisted by
a midwife. The skin is cleansed with antiseptic lotion. A fine,
sterile needle is passed through your abdomen (tummy), and
a small amount of amniotic fluid (15-20 mls) is removed. The
amount removed is a tiny amount of the total and this will not
affect the baby. Your body will naturally make more fluid to
replace that removed.
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Does it hurt?
Although you will be aware of what is happening, most women
say afterwards that it is no worse than having blood taken,
or having an injection, and that the thought is worse than
the actual test. You may experience a cramp-like discomfort.
Local anaesthetic is not often used for this test, as this may be
more uncomfortable than the actual test.
What are the risks?
We take care to reduce the risks to you and your baby.
The test does carry a small risk of miscarriage. 1 in 100 women
will have a miscarriage following the test. (RCOG)* You should
consider this risk when deciding whether or not you wish to
have the test.
Because the test uses the ultrasound scan, injury to the baby is
avoided and is very rare.
Sometimes the laboratory is unable to test the sample, for
example, if there are not enough of the baby’s cells within that
sample or if the cells do not grow. It is not possible to judge the
quality of the sample in advance. If this happens, the test will
need repeating, although this happens very rarely and will be
discussed with you.
What happens after the test?
Most women feel fine after the test, although we suggest you
remain in the clinic for about 20 minutes afterwards. We advise
that someone else drives you home.
We suggest that you take it easy for a couple of days after the
test. Avoid heavy lifting and strenuous exercise. Ordinary every
day activity will not cause you to have a miscarriage.
Following the test some women may experience cramp like
abdominal (tummy) pains, and may feel a little sore for 1-2
days. This is quite normal. You can safely take mild painkillers
as advised by your midwife or doctor.
If your blood group has shown you to be rhesus negative, you
will need an injection of Anti-D following the amniocentesis.
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It is rare to experience serious complications, but the signs to
be aware of are:
■
Heavy vaginal bleeding (slight spotting is normal).
■
Leakage of fluid from the vagina.
■
Painful “period-like” abdominal (tummy) pain that does not
ease or go away with paracetemol.
■
A raised temperature or general feeling of being unwell.
In the event of these symptoms, or if you have any concerns,
contact your community midwife or Doctor. The number is in
your maternity record book.
Is it an accurate test?
The test is reliable for Down’s Syndrome and for some other
chromosome problems, but it is not possible to detect all genetic
problems. It is accurate in determining the sex of the baby.
When do I get the result?
The result comes in two parts:
Part one: This result is usually available in about 3 working
days. This part of the test can only tell us about chromosomes
13, 18 and 21.
Part two: The confirmatory (final) result is available after
about two weeks. This tells us about all the chromosomes.
We will arrange with you how you would like to receive the result.
Once we have received the confirmatory (final) report, we
will send you a letter for a normal result, but will contact you
by telephone if a problem has been identified (shown).
In the event of an abnormal result, you will be offered an
appointment to come back to the antenatal clinic for a
discussion about what to do next, and to help you to make
decisions about how you would like to manage your pregnancy.
Diagnostic testing in pregnancy
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References and sources of further information
Royal College of Obstetrician & Gynaecologists (RCOG)* (2000)
Clinical green top guidelines. Amniocentesis (8).
Bui, T.H., et al. (2002 ) Prenatal diagnosis: molecular genetics &
cytogenetics) Best Practice & Research. Clinical Obstetrics &
Gynaecology.
Bui, T.H. et al (2002) Prenatal diagnosis: molecular genetics &
cytogenetics. Best Practice & Research. Clinical Obstetrics &
Gynaecology.
Antenatal Results & Choices (ARC) 0207 631 0285
www.arc-uk.org
Contact a Family (CAFAMILY) 0808 808 3555
www.cafamily.org.uk
DIPEx
www.healthtalkonline.org & www.youthhealthtalk.org
Down’s Syndrome Association (DSA) 0845 230 0372
www.downs-syndrome.org.uk
Sickle Cell Society 0208 961 7795
www.info@sicklecellsociety.org NHS Constitution. Information on your rights and responsibilities.
Available at www.nhs.uk/aboutnhs/constitution
[Last Accessed March 2010]
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How to contact us:
H
If you have any other
questions or if you would like
more information you may
contact your own midwife or Doctor (GP)
Alternatively, contact the
Antenatal screening midwife
at Southmead Hospital
Antenatal Clinic
0117 323 2465
www.nbt.nhs.uk
If you or the individual you are caring for need support reading this leaflet please ask a member of staff for advice.
© North Bristol NHS Trust. First Published December 2005. This second edition June 2010. NBT002206