Genetic Counselling

Genetic Counselling maybe offered by your own doctor or alternatively is available at the practice prior to C.V.S. and other procedures. This is to help you understand both the test itself plus birth defects and inherited conditions in general; it also allows relevant family medical and pregnancy information to be checked to assess your specific risks. You will then be informed of the risks, benefits and limitations of testing to you. You can choose the course of action that is appropriate to you in view of your own specific family needs and goals.

We recommend counselling on a day prior to the procedure to enable you to better consider your options, but it is available also at the practice on the day of the procedure.

Who is offered C.V.S. ?

Women of 37 years and over at the estimated time of delivery are routinely offered testing in Victoria. Some younger women may also be offered it (in many other states of Australia and other countries it is offered at 35 years and sometimes even younger).

Other reasons for offering C.V.S. include:

• Women who already have a child with chromosomal problem such as Down Syndrome.
• Women who know that an inherited disorder runs in their family or in the family of their partner.
• Occasionally C.V.S. is performed for other reasons.
  These include couples who are known to have a chromosome abnormality themselves, plus those who are known to be at risk of having a baby with one of a number of rare disorders.

C.V.S. cannot test for spina bifida. Unlike Down Syndrome, spina bifida is not more common in pregnancies of "older" women. An ultrasound examination at 18 to 20 weeks can detect many physical abnormalities of the fetus, including spina bifida.

Why are older women offered C.V.S. ?

As the woman's age increases her chance of having a baby with a chromosome abnormality, such as Down Syndrome, also increases. The chance of Down Syndrome is the same whether or not this the first child.

In each human cell there are 46 chromosomes, each of which is paired giving 23 different chromosome pairs. The only exceptions are the egg and sperm which each have 23 chromosomes. Each chromosome contains thousands of genes which control an individual's growth and development. Birth defects may result if there are too many or too few chromosomes. The best known chromosome abnormality in newborn babies is an extra chromosome 21 so that the baby has 47 chromosomes in the cells instead of the normal 46. This causes a condition known as Down Syndrome (previously known as mongolism). A chromosome abnormality cannot be cured or corrected.

The chance of having a live born baby with Down Syndrome when you are aged 37 years is approximately 1 in 220. The chance at 40 years is approximately 1 in 90. The chance of having a live born baby with any chromosome abnormality is about double these figures. With increasing age there is no increase in the chance of having a baby with spina bifida. Most other abnormalities also do not depend on the age of the pregnant woman so that if the chromosomes are normal then most of the increased risk in 'older' pregnant woman has of delivering a baby with an abnormality is removed.

It is important when looking at the chance of a baby having a chromosome abnormality to keep the figures in perspective:

• approximately 4% of babies have some abnormality at birth and most of these have normal chromosomes.
• chromosome abnormalities are rare compared to many of the other risks of pregnancy, for example 5% of babies are born early.

What type of disorders can be detected by C.V.S. ?

• Chromosome abnormalities
• Some inherited disorders when couples are known to be at high risk
• C.V.S. is not a general test for the fetus - it tests only for very particular problems, usually only chromosomal abnormalities.

When is C.V.S. carried out?

C.V.S. may be performed anytime from 10 weeks onwards.

Why is an ultrasound scan needle before C.V.S. ?

An ultrasound scan is carried out to confirm the age of pregnancy, to make sure there are not twins and to check that the pregnancy appears healthy. The fetus is still small so very few physical abnormalities can be detected at this stage.

One part of the fetus which is carefully examined at 10 weeks is the back of its neck looking for evidence of swelling. If there is subtle swelling in this area then there is an increased chance of Down Syndrome.

What should I do before the test ?

A full bladder is not required.

On the day of the test you should expect to be at our premises for one to one and a half hours.

What happens on the day of the test?

We use transabdominal C.V.S. Nitrous oxide gas, the gas used in labour, is available for the procedure if you wish to have it. This helps to keep you comfortable during the test, but does not put you to sleep.

A fine needle is passed through the skin and into the uterus to the edge of the placenta, The path of the needle is followed carefully on the ultrasound screen. A finer needle is then passed through the outer needle into the placental tissue. A syringe is used to draw up very small fragments of placental tissue. The tissue is examined to make sure it is adequate. If required, further aspirations are performed through the inner needle without any additional discomfort. The needle at no time is passed into the amniotic sac - this helps minimise the risk of the test, and any movement of the fetus during the test causes no concern. It usually takes only 1-2 minutes to perform the test. At the end of the procedure the fetus is checked and you are able to leave the room immediately. After waiting for about 30 minutes you are then able to go home.

The amount of discomfort with C.V.S. varies, but patients who use the gas have very little pain.

Chorionic villus sampling (CVS), using the transabdominal technique: a needle is passed through the abdomen down into the placenta.

What is done with the cells?

The cells obtained at C.V.S. are allowed to grow in the laboratory until there are enough for testing the chromosomes. Each of the chromosomes is carefully examined to check that there are the correct number and that the appearance and the length of each chromosome is normal. If the fetus has Down Syndrome (mongolism) then there is an additional 21 present. The sex of the fetus can also be determined by looking at the chromosomes - you can find this out if you ask your doctor.

The laboratory will usually have the result available within 2 weeks - your doctor will be informed and he or she will pass it on to you.

How will I feel afterwards ?

Most people appreciate having a companion to drive them home after a C.V.S.

It is recommended that you rest for the remainder of the day, although there is no reason to go to bed. There need be no further limitation of routine after this time.

If it takes more than one or two hours to travel home, it is preferred that patients stay in Melbourne overnight after the procedure.

After C.V.S. some women feel lower abdominal discomfort or period like pains and some may feel faint for a short time. These symptoms are not associated with any risk to the pregnancy. It is very uncommon to have any bleeding after transabdominal C.V.S.

What are the risks of the test?

A study which included Lachlan de Crespigny's patients suggested that the risk of miscarriage from C.V.S. itself is 1 in 100 or less. (There is also the natural miscarriage rate which is approximately 1 in 50 after 10 weeks whether or not you have a C.V.S).

Patients often ask when a miscarriage might occur after C.V.S. Because most miscarriages are after C.V.S. are "natural" miscarriages which are unrelated to the test this is a difficult question to answer. If however there has been no problem by three weeks after the test then any complications would be unlikely to be due to the test. The chance of complications is very much related to the experience and expertise of the operator.

Research has suggested that there might be a slightly increased risk of limb defects when a C.V.S. has been performed, prior to 9 weeks. There is however no evidence of C.V.S. causing limb defects at the time we offer the test, ie at 10 weeks or more. Other rare complications include bleeding, infection and ruptured membranes.

Complications to the pregnant woman herself are extremely rare. If your blood group Rh negative you should have anti-D after the C.V.S., although if your doctor has indicated that you have antibodies then amniocentesis is preferable.

C.V.S. like any test may fail because an inadequate sample is obtained or because the laboratory cannot produce a result. Both of these risks are very uncommon.

Incorrect results are possible but are extremely rare. In approximately 1% of patients uncertain results occur which may need a further test (usually amniocentesis) to sort them out.

What Should I look for after the test?

If there is any blood or clear fluid from the vagina, you should consult your own doctor.

What does a test cost ?

Details of charges are available from our practice. We will give you an account for the test itself plus the laboratory will separately send an account for laboratory services plus any necessary blood test. Medicare will cover part of the cost for each of these accounts.

What if the results show an abnormality is present?

Those few patients in whom the test shows that the fetus has an abnormality will be given information so that they can make a choice about whether to continue the pregnancy. Counselling is available. If a couple decide to terminate the pregnancy, because of an abnormality detected at C.V.S., the procedure is usually a straight forward 'D & C' in hospital.

What alternative methods are available to test the chromosomes?

C.V.S. can also be carried out via the transcervical approach. This involves passing a tube (canula) through the neck of the womb (cervix) into the placenta tissue. In our hands, a transabdominal approach is safer.

The chromosomes may also be tested by amniocentesis - a pamphlet is available for this test.

Should an ultrasound examination be performed later in the pregnancy?

Since few physical abnormalities of the fetus can be detected using ultrasound at the time the C.V.S. is carried out, most obstetricians would suggest a further scan at 18 to 20 weeks.

Summary

C.V.S. is most commonly performed to exclude Down Syndrome and other abnormalities because of the age of the pregnant women. It cannot be used to diagnose spina bifida but this and other abnormalities can be diagnosed with an ultrasound examination at 18 to 20 weeks.

C.V.S. has perhaps a slightly higher risk of causing a miscarriage than amniocentesis. The attraction of C.V.S. is that the results are available relatively early in pregnancy - hence if there is an abnormality and you decide to terminate the pregnancy, this can be performed as a simple 'D & C' (Curette).

It is important to appreciate that no test, even a combination of a C.V.S. and a careful scan at 18 weeks, guarantee that the baby will be normal in every respect.

If you would like more information, please ask. If you would like more written information we have pamphlets available on ultrasound and amniocentesis. For more detailed information you may purchase Lachlan's book "Which Tests For My Unborn Baby? A Guide to Prenatal Diagnosis",(OUP) which is available at a reduced price at our practice.