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Amniocentesis and Chorion Villus Sampling


What is amniocentesis?

Amniocentesis involves withdrawing a small quantity of fluid from around the baby in order to examine cells that originate from the baby. In other words, through such an examination we can eventually diagnose chromosomal abnormalities, the most frequent being trisomy 21.

Whom is amniocentesis indicated for?

In general, amniocentesis is indicated for women at high risk of carrying a baby with chromosomal abnormalities, an example being trisomy 21. Such a risk increases with maternal age. Some doctors propose amniocentesis to all pregnant women from 35 years onwards. However an alternative is to combine the risk based on maternal age with the measurement of the fetal nuchal translucency as well as serum biochemistry markers. In case the combined risk is higher than a certain cut-off, an amniocentesis could be proposed in order to analyse the chromosomes of the baby.

The practitioner can also indicate an amniocentesis in other circumstances, such as for example in case of past history of genetic disease in the family or suspicion of congenital infection. In such cases, specific analysis on the amniotic fluid will be performed. Finally, amniocentesis can also be indicated in case, during the 2nd or 3rd trimester morphological scan, suspect abnormalities are detected bu the sonographer.

Practically how does the amniocentesis happen?

Amniocentesis is generally performed in an ultrasound room, from 16 weeks of gestation onward. The procedure lasts less than a minute, generally not painful, therefore a local anaesthesia is not needed. Amniocentesis involves passing a thin needle into the uterus, under ultrasound guidance. The fluid removed reaccumulates generally within a few hours.

Subsequently, the sample is send to the laboratory. For a full karyotype, the results are know 3 weeks later, however for a more specific indication, results could be obtained rapidly within a couple of days.

What to expect after amniocentesis?

For the first couple of days you may experience some abdominal discomfort or period-like pain. You may find it helpful to take simple painkillers like paracetamol. However, if the pain persists, if you experience bleeding, loss of fluid or high temperature, it is recommended that you directly get in contact with your gynaecologist.

What are the risks associated with amniocentesis?

Amniocentesis carries a 1% risk of miscarriage, often occurring within the week following the procedure.

Is there an alternative to an amniocentesis?

Amniocentesis is not obligatory. It will be proposed to couples and it is only after weighing the pros and the contras that a couple can decide to have it done or not. It is recommended that counselling concerning the indication of an amniocentesis is performed by maternal fetal medicine specialists.

Amniocentesis remains fully re-imbursed by the national health care system or INAMI in Belgium, for whatever risk for trisomy 21. In neighbouring countries, an amniocentesis is only re-imbursed in case there is a high risk for trisomy 21. It is likely than during 2013, the same rules will also apply to Belgium.

Since January 2103, a new test can be proposed as an alternative to amniocentesis for trisomy 21. It is a simple blood test drawn from the mother, thus a non-invasive prenatal test or NIPT that allows in nearly 100% of cases to detect trisomy 21, without any risk of miscarriage. Unfortunately, such a test is still completely to be paid by the parents.

Chorion Villus Sampling (CVS)

What is chorion villus sampling?

Chorion villus sampling (CVS) involves the examination of placental tissue, without the need to enter into the amniotic sac. Since both the fetus and the placenta originate from the same cell, therefore the chromosomes present in the cells of the placenta are the same as those of the baby.

What are the indications for a CVS?

The indications for a CVS, besides rare exceptions, are the same as for an amniocentesis. The most common indication concerns women at high risk of carrying a fetus with a chromosomal abnormality.

How is CVS done in routine practice?

As for an amniocentesis, CVS is performed in an ultrasound room. It has the advantage of being performed earlier as compared to amniocentesis, since a CVS can be performed from as early as 11 weeks of gestation and usually until 16 weeks of gestation. The procedure last for less than a minutes and is performed under local anaesthesia. A fine needle is then passed through the mother's abdomen and a sample of villi is taken. The needle is carefully observed using ultrasound scan. The procedure is usually performed threw the mother’s abdomen, in about 99% of cases. Rarely, a vaginal CVS is necessary.

Subsequently, the sample is send to the laboratory. For a full karyotype, results are often known after 2 to 3 weeks. However, for specific indications, results could be obtained in a week or less.

What should I expect after the CVS?

For the first couple of days you may experience some abdominal discomfort, period-like pain or a little bleeding. Simply taking paracetamol as a painkiller should be helpful. However, if there is a lot of pain or bleeding or if you develop a temperature please seek medical advice.

What are the risks associated with the test?

The risk of miscarriage due to CVS is about 1% and this is the same as the risk from amniocentesis at 16 weeks. In approximately 1% of cases the invasive test will need to be repeated because the results are inconclusive.