Amniocentesis

Amniocentesis is a diagnostic test in which a small amount of the amniotic fluid surrounding the baby in the uterus (womb) is removed by passing a fine needle through the mother’s abdomen.

Amniocentesis is usually offered to women who have an increased chance of having a baby with a disorder. It is not usually offered on a routine basis. If a disorder is diagnosed, then you should be given information and the opportunity to discuss this with a specialist.

With an experienced clinician, the risk of blood stained amniotic fluid is less than 1% (that is, less than 1 in 100 tests).

You will be asked to sign a consent form before having amniocentesis.

Why is Amniocentesis carried out?

One of the main reasons amniocentesis is used is to detect whether or not a baby has a chromosomal disorder, such as Down syndrome. However amniotic fluid can be analysed (tested) in several different ways and ultimately the analysis will depend on the reason why amniocentesis is being considered.

Amniotic fluid contains lots of different elements floating in it. It is these elements, such as baby skin cells, viruses and waste products from the baby that can be analysed to provide a diagnosis.

When is Amniocentesis carried out?

The safest time to have amniocentesis is after 15 weeks of pregnancy.

How is Amniocentesis carried out?

Pre-procedure preparation

A scan is performed just prior to the procedure to check:

  • The position and size of the baby (If less than 14 weeks, amniocentesis will be postponed)
  • The position of the placenta (afterbirth)
  • The amount of amniotic fluid around the baby.

The area of skin of your abdomen (tummy) covering the site being used for the amniocentesis needle will be thoroughly cleaned. Sterile drapes will then be used to cover most of your abdomen. The scanner probe head is covered with a sterile plastic bag. The doctor will wash his hands and put on sterile gloves. All this careful preparation is to ensure that the procedure is carried is carried out in as clean an environment as possible, as this will help to reduce the risk of procedure-related infection to you and your baby.

Procedure

A fine needle is passed through the abdominal skin, through the wall of the uterus and into the pool of amniotic fluid. This skilled procedure will be carried out under direct scan guidance for the entirety of the procedure. Once the needle is in the pool of amniotic fluid, a small sample of that fluid is taken using a syringe. The size of the sample is usually between 10-20mls (1-2 tablespoonful). Taking this amount of fluid will not affect the pregnancy and will soon be made up and replaced by the baby. You will be asked to check your personal details on the label of your amniotic sample before it is sent to the laboratory. Once the procedure is finished you will be shown the baby’s heartbeat for reassurance.

Post-procedure

An amniocentesis procedure will take 15-20 minutes to be carried out and you will be asked to rest for 15-30minutes before going home. Some women may feel some discomfort following the procedure. It would be unwise to leave the hospital if you are feeling unwell or uncomfortable and we always advise you to rest until you are fit to travel. Before you leave the hospital, details on how you wish to receive your result will be checked with you, as well as contact telephone number and/or address. We would advise you to rest and take life easy for at least two days following an amniocentesis procedure. If you have any worries or concerns please don’t hesitate to contact us or contact your local Maternity Unit. If your blood group is Rhesus negative, will be offered an Anti D injection.

Will it hurt?

You will find that there may be some discomfort during and for s short time after the amniocentesis procedure. It is not that unusual to have mild period-like cramps after the procedure, but with rest this discomfort will soon wear off.

Will amniocentesis give a definite result?

The amniocentesis will give you a definite result, but there are some exceptions to this (such as culture failure) and this will be discussed with you during the pre-procedure counselling. The result sometimes can be somewhat unexpected, e.g. a mother may have an amniocentesis based on her concern about having a baby with Down syndrome and the result may be abnormal but not for Down syndrome. Occasionally the result can be difficult to interpret. In these cases, further follow-up by referral to a Genetics Department is usually needed.

How long does it take for an amniocentesis result?

Because amniocentesis is carried for several reasons, the answer to this question is when the result is ready. To explain further, it can take up to 2 weeks to get a chromosome result but a result to check for viruses may only take one week. The timing of your result will be discussed with you during pre-procedure counselling. On some rare occasions, the cells collected to check the baby’s chromosomes can be very slow growing or fail to grow at all. You will be kept informed if this likely to happen. In these cases it is best just to wait for the slow growing cells mature or if there is no growth at all you may want to consider having a repeat test.

Is the procedure dangerous for the baby?

About 1 in every 100 women (or 1%) who have amniocentesis from 15 weeks of pregnancy under ultrasound guidance miscarry as a result of the procedure.

This procedure is ALWAYS carried out under scan guidance. By doing this great care is taken to avoid the areas of the baby that can be seriously damaged by needle-stick injury.

Will the baby be affected by the decrease in the amount amniotic fluid after amniocentesis?

The baby will quite normally, and naturally, replaces the amniotic fluid a few times every 24 hours anyway. The amount of fluid removed for amniocentesis procedure purposes is small when compared to the total volume of amniotic fluid left. Therefore any deficit of amniotic fluid is fairly quickly made up following amniocentesis.

If I were to miscarry, when is this likely to occur and is this the only problem I have to look for following an amniocentesis?

The risk of miscarriage can be present for several weeks following an amniocentesis. In our experience, it is not uncommon for women to have period-like pain, blood spotting or fluid loss via the vagina in the first week or so following an amniocentesis. By no means will all these women go onto miscarry, as in most cases these symptoms will settle down and the pregnancy will proceed as normal. If amniocentesis is undertaken then there is a 1:300* risk of miscarriage (or a 1% risk of premature labour if done after 24 weeks) within 3 weeks following the procedure. This is why only doctors who are specially trained are allowed to carry out this skilled procedure. It is important that if you are worried by any of the symptoms, that you follow the contact instructions contained in — “What you need to look out for following an amniocentesis” which can be found in the end paragraph.

Is there anything I can do to help prevent a miscarriage?

No not really, but we do advise the following:

  • Rest after the procedure and only leave the hospital when you feel absolutely fine.
  • Plan to rest for a couple of days, but bed rest is not necessary.
  • Avoid strenuous tasks or exercise, but light duties and gentle walks are fine.
  • Avoid intercourse for a couple of days.
  • Take pain-killing tablets, such as Paracetamol, if you experience any pain or discomfort. (Follow the dosage instructions on paracetamol packaging).

How should you prepare for Amniocentesis?

It is very important that you fully understand what will be involved in having an amniocentesis, so be absolutely sure you know what the procedure and risks involved are. Written information and information counselling services are available from the Fetal Medicine Department for you to make use of.

Discuss how you would like to have your result given to you, e.g. by telephone, by letter or by appointment. It is always wise to discuss with your partner issues surrounding an abnormal result and what your likely choices would be in this difficult situation.

What do you need to look out for following an amniocentesis?

You should contact us or your local Maternity Unit if you experience any of the following:

  • Severe pain that is not controlled with simple analgesia such as paracetamol tablets.
  • Any bleeding, fluid loss or unpleasant discharge from the vagina.
  • Abdominal cramps or tightenings.
  • If you feel that you have a temperature or a very fast pulse.
  • If you feel ill or unwell.

Further information and a PDF leaflet are available from the Royal College of Obstetrics and Gynaecology.

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