What are amniocentesis and CVS, and for whom are they recommended? How they are done, the miscarriage risk, care afterwards and what results mean.
Amniocentesis and CVS (chorionic villus sampling) are diagnostic procedures in which a small sample is taken from the fluid around the baby or from placental tissue and the baby's genetic structure is examined. They are not screening tests; they are decided with the doctor, to confirm or rule out a particular condition when a screening result shows a high probability, when there is a history of genetic disease in the family or when a finding is seen on ultrasound. They are not a routine practice and are optional. The procedures carry a risk of miscarriage, although a small one. Mild cramping after the procedure may be usual.
Are a screening result and a diagnostic test result the same thing?
Screening tests estimate the likelihood of a condition, while diagnostic tests try to determine whether a particular condition exists. Diagnostic and screening tests are assessed separately. When screening shows a high probability, the option of a diagnostic test, or of not having an additional test, is discussed with the doctor.
What is the difference between amniocentesis and CVS?
In amniocentesis, a thin needle is advanced through the abdominal wall under ultrasound guidance and a sample is taken from the amniotic fluid that surrounds the baby. In CVS, on the other hand, a cell sample is taken from a part of the placenta (the chorionic villi); this is done mostly through the abdomen and, in some situations, through the cervix.
The most marked difference between the two is timing: CVS is done at an earlier stage of pregnancy and amniocentesis in the second trimester. Neither procedure should be done below its own earliest limit. Amniocentesis is done later and its results also come later. Which is suitable is determined together with the doctor according to the indication and the stage of pregnancy.
For whom are they recommended, and why?
These procedures are considered when a screening test shows a high probability, when an earlier pregnancy or baby was affected by a genetic condition, when there is a history of genetic disease in the family or when a finding has been seen on ultrasound. Among the conditions that can be looked for are Down syndrome, Edwards and Patau syndromes, and diseases such as sickle cell disease, thalassaemia and cystic fibrosis. Which genetic analysis will be done is determined by the doctor and the laboratory according to the reason for the procedure.
The procedure is optional. That it is offered does not mean it is compulsory; a detailed counselling consultation is recommended before making the decision.
How is the sample taken during the procedure?
The procedure is mostly applied in a hospital setting, under ultrasound guidance. The sample taken is examined in the laboratory.
What can you feel during and after the procedure?
In CVS the procedure generally gives a feeling of discomfort rather than pain, and period-like cramping may be seen for a few hours afterwards. The feeling varies from person to person; you can ask your doctor what you may feel before the procedure.
How should you prepare before the procedure?
On subjects such as fasting, medicine use and rest after the procedure, the instruction of your doctor or the centre where the procedure will be done applies. It is recommended that the status of blood-borne viruses be assessed before the procedure; your blood group may also come up at this consultation.
Is there a risk of miscarriage from the procedure?
In experienced hands, the additional risk of miscarriage related to the procedure in a singleton pregnancy is small, but it exists; in a twin pregnancy this risk is higher. Estimates of the size of the risk vary with the study and the period. Most miscarriages are seen in the first days after the procedure; some can appear in later days.
Besides miscarriage, which risks and symptoms are important?
Infection is rare. Leakage of fluid and bleeding are also among the situations needing attention after the procedure. If the sample falls short, the procedure may need to be repeated.
What is expected after the procedure?
In the first days after the procedure, mild abdominal pain or cramping may be usual; rest is recommended in this period. Follow your doctor's instructions on the use of painkillers. The time for returning to daily life depends on your doctor's instructions.
Do the results come all at once?
The results may come not all at once but in several stages: a rapid preliminary result for some common conditions, and a more detailed result for more comprehensive analyses. Your doctor or the laboratory will tell you how long this will take.
Does a normal result show that your baby is healthy in every respect?
The result gives information only about the conditions analysed; it says nothing about the conditions not looked at. If the sample is insufficient or the result is not clear, reassessment may be needed. For this reason a normal result does not show that the baby is healthy in every respect.
How can you discuss your options and need for support after the result?
Your doctor and the healthcare team discuss with you the options after the result. This process can lead to intense feelings; in this case you can be referred to support organisations. You can ask your doctor about counselling or mental health support.
What can you ask your doctor before deciding on the procedure?
- Ask which procedure is being recommended for what reason and what the alternatives are.
- Tell your doctor your blood group and, if you have one, a diagnosis of chronic infection.
- Find out whether your pregnancy is single or multiple and how this affects the risk of the procedure.
- Ask for written instructions that you need to follow on the day of the procedure and afterwards.
- Ask by whom, by what route and when the results will be communicated.
Frequently Asked Questions
My blood group is Rh negative; is an injection needed after the procedure?
In Rh-negative blood group, a protective injection is recommended to prevent the problems that Rh incompatibility between mother and baby can cause. Whether the injection is needed for your procedure in the case of CVS is determined by your doctor, who knows your blood group.
Does the needle touch the baby during the procedure?
No. In amniocentesis the needle is guided under ultrasound imaging and kept away from the baby. This precaution does not mean that the procedure has no risks; the risks are described above.
I carry hepatitis B, hepatitis C or HIV; can the procedure be done?
In mothers who carry one of these infections the risk of passing it to the baby may increase; for this reason the subject needs to be discussed with a specialist doctor and the status of the virus needs to be assessed before the procedure. Pass on your information to your doctor beforehand; whether the procedure is suitable for you is decided with this information.
Are amniocentesis and CVS screening tests?
No. They are diagnostic procedures aimed at confirming or ruling out a particular condition. Which analysis will be done is determined according to the reason for the procedure.
Does a procedure being recommended mean I have to have it?
No. The procedures are optional. Before deciding you can receive detailed counselling and discuss with your doctor the options of a diagnostic test or of not having an additional test.
Is the sample taken from the same place in amniocentesis and CVS?
No. In amniocentesis the sample is taken from the amniotic fluid, and in CVS from placental tissue.
Are the two procedures done in the same period of pregnancy?
No. CVS is done earlier and amniocentesis in the second trimester. Each procedure should not be applied below its own earliest limit.
Is there no risk of miscarriage at all from the procedure?
No. In experienced hands, the additional risk in a singleton pregnancy is small, but it exists. In a twin pregnancy the risk is higher.
Does a normal result show that the baby is healthy in every respect?
No. The result gives information only about the conditions analysed. It does not rule out conditions that were not examined.
If the sample is not sufficient, may reassessment be needed?
Yes. If the sample is insufficient or the result is not clear, reassessment and, in some situations, repetition of the procedure may be needed.
Do all the results come at the same time?
No. A rapid preliminary result may come for some conditions and a detailed result for more comprehensive analyses. The doctor or the laboratory will tell you the time to be waited.
Can mild cramping occur after the procedure?
Yes. In the first days mild abdominal pain or cramping may be usual. Follow your doctor's instructions on rest, the use of painkillers and returning to daily life.
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