Leeds Fetal Medicine Unit Website

Amniocentesis

Amniocentesis is the process of removing amniotic fluid (the fluid surrounding a baby in the womb). This is done primarily to aid diagnosis of chromosomal and genetic conditions, but is occasionally performed to reduce the amniotic fluid volume as part of amnioreduction in conditions where excess fluid accumulates. Prior to performing the test all women will initially undergo a detailed ultrasound scan of the baby's anatomy to confirm gestation and look for any abnormalities or signs that may aid the laboratory when testing the sample. Once gestation has been confirmed at 15 weeks or more (amniocentesis is not performed at early gestations in Leeds) the abdomen (tummy) is cleaned and a fine needle inserted under direct ultrasound vision so that we can avoid the baby(see Picture ?number below).

As a very fine needle (20-22 guage needle) is used we do not use local anaesthetic and most women find the procedure comparable to the discomfort experienced from having blood taken. Approximately 15mls of fluid is removed which is then sent to the laboratory for analysis. In the laboratory skin cells shed by the baby during growth are isolated and from the fluid removed, and it is from these that we can determine genetic information about the baby. Usually these isolated cells are tested using the rapid PCR test which looks for the three most common abnormalities at 15 weeks or more gestational weeks. Results as to whether the baby has Down's synrome (an extra chromosome 21), Edward's syndrome (an extra chromosome 18) or Patau's syndrome (an extra chromosome 13) are usually available 24-48 hours later. If the scan is abnormal or if there are other factors in individual cases, the isolated cells are also cultured for a further 18 days; at this point all chromosomes are examined for number and size.

Following the procedure you will be allowed home where we will ring you with the results when they are available.

Important - Risks associated with Amniocentesis

Like any invasive procedure to obtain genetic information about a baby, amniocentesis can potentially cause a miscarriage to occur. The national figure for this based on published research is 1%. This means that 1 in 100 procedures performed will cause a miscarriage to occur whether the baby has normal or abnormal chromosomes. It is unknown why this occurs, but may be related to infection. In our unit audit we audit our figures to determine what the miscarriage rate following the procedure is in our hands, click here to see our current results.

For a pateint information sheet (in pdf format) click here

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