WHAT TYPES OF DISORDERS CAN BE DETECTED BY CVS?

(1) Chromosomal abnormalities.

(2) Some inherited disorders. Dominant, Recessive and X-linked patterns of inheritance.

WHO MAY BENEFIT FROM A CVS?

                    1)   Women over 35 (for first as well as subsequent pregnancies).

                    2)   Women who have had a child with a chromosomal abnormality such as Down syndrome.

3)  Women who are at risk for an inherited disorder that runs in their family or their partner’s family, which can be prenatally diagnosed. An example of this is Cystic Fibrosis.

WHY DO YOU NEED AN ULTRASOUND SCAN WITH CVS?

The scan locates the position of the chorion (placental tissue) which will be sampled. The ultrasound scan can also tell whether you are carrying twins and is used to measure the baby to determine the age of the pregnancy. During the CVS, the ultrasound allows the doctor to follow the sampling procedure visually and ensures the procedure is carried out safely.

WHAT HAPPENS DURING THE CVS?

A very small amount of the placental tissue (chorionic villi) is taken during this test. The amount of tissue needed for the analysis in the laboratory is extremely small and represents only about 1/1000 (0.1%) of the total amount of the placental tissue.

It is not feasible at present to test the cells for all the possible abnormalities that could affect the baby. Discuss with your doctor the disorders which might be detected. There are two different methods used to sample the chorionic tissue. The selection of the most appropriate method will be discussed with you.

Vaginal CVS

Vaginal CVS is very similar to having a PAP smear test. While the ultrasound is being used on the abdomen to locate the baby in the uterus, a speculum is inserted into the vagina so that the cervix can be clearly seen by the doctor. The cervix is swabbed with antiseptic to clean the cervix and remove mucus that is usually present and a cannula (fine hollow tube) is passed through the cervix into the uterus. The image of the cannula can be clearly seen in the ultrasound picture and thus it can be guided to where the placenta is forming. A small sample of the chorionic villi is removed from the placenta.

Abdominal CVS

Abdominal CVS is performed in a similar way to Amniocentesis (see later). The chorionic villi sample is obtained by passing a fine needle through the abdominal wall and into the placenta using ultrasound for guidance. A local anaesthetic is usually used to numb the area where the needle is passed prior to the procedure. Most women find the local anaesthetic quite uncomfortable.

WILL THE TEST HAVE TO BE REPEATED?

More than one CVS is very occasionally necessary to obtain a diagnosis. This happens when the doctor is unable to obtain enough tissue at the first attempt, or when the laboratory is unable to make an analysis of the tissue. Samples of the tissue are examined immediately (under a microscope) to make certain enough tissue is collected. If not enough tissue is collected, another sample may need to be taken at this time.

Rarely, the laboratory may be unable to make an analysis of the tissue and then another CVS may have to be done at another time.

On rare occasions, there is a need for an Amniocentesis to be done later to confirm a diagnosis. This means that a very small number of women (less than 1%) have both a CVS and an Amniocentesis.

WHAT WILL THE CVS TELL US ABOUT THE BABY?

Doctors and scientists are now able to diagnose a large number of disorders prenatally. It is not feasible to test the cells for all the possible abnormalities that could affect the baby. Discuss with your doctor the range of disorders which might be detected.

It is important to remember that a normal test result cannot exclude every possible problem with the baby. Not all birth defects can be detected by these tests.

WHERE WILL THE TEST BE DONE?

All CVS are done as an outpatient test (you do not need to be admitted to hospital) performed in the Fetal Medicine Department, Royal Hospital for Women, Barker St, Randwick, by doctors who are experts in doing this procedure. There is no need to fast before the test.

WHEN WILL THE CVS BE DONE?

The test is performed from the 10th to12th week following the first day of the last menstrual period. It is important to see your doctor as soon as you realise you are pregnant.

In special circumstances, the CVS may be carried out later in the pregnancy. However, it should not be done before the 10th week of pregnancy.

WHEN WILL THE RESULTS BE AVAILABLE?

The result is usually available in 2 weeks (occasionally the cells grow slowly and they can take 3 weeks). The cells making up the chorionic villi usually have the same genetic information as the developing baby and are allowed to grow and multiply in a laboratory until there are enough for testing.

DOES THE CVS HARM THE PREGNANT WOMAN OR THE UNBORN CHILD?

It is important that CVS is only carried out by a doctor experienced in this technique and should be done only after the 10th week of pregnancy. Studies have shown that the miscarriage rate related to the test is about 1- 1½ % (about 1 in 50 pregnancies). This figure does not  include those women who would have miscarried without the test. Should a miscarriage related to the procedure occur, it usually happens within a few weeks of the test.

Some women experience cramping and occasionally, some vaginal bleeding after CVS. These symptoms are normal and should only last a day or so. You should contact your doctor if you are concerned.

Parents are often concerned that the cannula (tube or needle) used to collect the tissue will hurt the baby, but the use of the ultrasound scanner during the procedure ensures that the instrument is outside the sac that the baby is in.

ARE ANY OTHER TESTS DONE?

As the CVS is performed early in the pregnancy, it is not possible to detect abnormalities such as neural tube defects (see Glossary). It is important to have a blood test (the alphafetoprotein test) in the 15^th-17^th week of pregnancy which can help find babies with neural tube defects and other abnormalities in the development of the baby.

An ultrasound between 18 and 20 weeks of pregnancy to look for other abnormalities is usually appropriate.

DISADVANTAGES OF DOING A CVS

1. The rate of miscarriage is higher than for an Amniocentesis

2. The chances of getting a placental 'mosaic' artefact is higher than with an Amniocentesis.  This implies the fetus is normal, but that some of the cells in the placenta have abnormal chromosomes.  Usually the only way to exclude a 'real' abnormality is by Amniocentesis.

3. AFP is not performed. This is not really an issue unless you are at increased risk of a neural tube defect.

 WHAT HAPPENS IF THE RESULTS 0F THE CVS SHOWS AN ABNORMALITY IS PRESENT IN THE BABY?

Most often, the baby will not have the particular disorder for which it was tested. In those few cases where the test does show that the baby has an abnormality, the expectant parents will be given as much information as possible to enable them to make a choice about whether to continue the pregnancy. Support and information is available to the expectant parents at this time. Formal genetic counselling is recommended.