What is a cordocentesis?

A sample of blood of the unborn baby (baby) is obtained by placing a thin needle through the abdominal wall into the umbilical cord.

The blood in the umbilical cord originates from the baby, and can be used to diagnose specific conditions of the baby.

Why would a cordocentesis be done?

A cordocentesis can be done for several reasons amongst which are:

  • To determine possible chromosomal abnormalities in the baby (e.g. Down syndrome)
  • To determine whether the baby is anaemic before an intra-uterine transfusion is done (e.g. in cases of severe rhesus iso-immunisaion, where the mother produces antibodies against the baby’s blood group.)
  • To determine whether the baby is affected by an virus infection , e.g. rubella (German measles)

Why would a cordocentesis sometimes be done instead of an amniocentesis?

  • The results of the chromosomal analysis are usually available within three days, instead of three weeks. A cordocentesis is therefore preferred to an amniocentesis if:
  • The decision to obtain a chromosomal analysis is made late in pregnancy (after 20 weeks), e.g. when an abnormality is seen on ultrasound.
  • An amniocentesis had been done, but yielded none or an ambiguous result.

Why would both a cordocentesis and an amniocentesis be done?

Usually, amniocentesis and cordocentesis are complementary where tests are done for anaemia or infections in the baby, and each tests provides information which is not obtainable from the other.

Why would a cordocentesis then not always be done instead of an amniocentesis?

Some information can be obtained from an amniocentesis which could not be obtained from a cordocentesis.

It is difficult to perform a cordocentesis before 18 – 20 weeks, because the blood vessels in the umbilical cord is very thin.

Who decides whether a cordocentesis should be done or not?

Your doctor (or sometimes, genetic counsellor) will discuss with you why a cordocentesis is offered. It remains your own decision whether or not to undergo a cordocentesis.

When would a cordocentesis be done?

The timing of the cordocentesis would be determined by the reason for the cordocentesis. It can be performed any time between 18 weeks and delivery.

Where would a cordocentesis be done?

The cordocentesis would be done in a sonar room.

How is a cordocentesis performed?

With an ultrasound examination, the position of the umbilical cord, the placenta (afterbirth) and the baby in the womb is determined. The best place for the cordocentesis is then determined.A nursing sister comes to assist your doctor. A thin needle is then placed through your abdominal wall into the umbilical cord,fetal blood is the collected, which will be sent for the different tests. Local anaesthetic may be used. The needle is removed, and the baby’s heart action is shown to you for reassurance.

If your blood group is rhesus negative, the baby’s blood group will be tested. If the baby is rhesus positive, you will receive an injection with anti-rhesus antibodies, to prevent your immune system from producing antibodies against the baby’s blood group.

What can go wrong with a cordocentesis?

During the cordocentesis

  • It can be difficult to obtain the fetal blood sample from the umbilical cord. This might necessitate a second puncture elsewhere on your stomach.
  • There can be bleeding from the umbilical cord. This can be seen on sonar, and usually stops within a few minutes.
  • There can be bleeding into the umbilical cord (a so-called “cord haematoma”), which can impair the blood flow to the baby. It is only a significant risk with an intra-uterine transfusion, or where the baby has a very low platelet count.
  • The baby can be injured by the needle. This risk is diminished by watching the needle by sonar throughout the procedure, and because the needle is positioned in the umbilical cord during the cordocentesis.

Due to these potential complications, a viable baby (e.g. more than 26 weeks of gestation) can be monitored in the hospital for about 30 minutes after a cordocentesis which is done in the third trimester.

After the cordocentesis

  • Amniotic fluid can leak out. This would happen about once in every 50 cordocenteses. If it does happen, you would notice a small amount of fluid leaking out vaginally. Usually, it resolves if you stay in bed for a week.
  • A miscarriage can occur. Symptoms of this are cramping abdominal pains, worse than menstruation pains, as well as vaginal bleeding. This would happen about once in every 100 cordocentesis. It can also present by reduced fetal movements. If you notice any of these symptoms, please contact your doctor immediately.
  • An infection can develop in the womb. Symptoms of this are fever, cold shakes, a constant pain over the womb, and sometimes an offensive vaginal discharge. If you notice any of these symptoms, please contact your doctor immediately.
  • If you are HIV positive, there is an increased chance that HIV can be passed on to your baby if you have an cordocentesis.

When would the results be available?

  • The result of the chromosomal tests, which would indicate whether the baby has Down syndrome or other chromosomal abnormalities, should be available within three days.
  • The baby’s hemoglobin count (which is done to determine whether the baby is anaemic) and the baby’s rhesus blood group, is done in the rooms, and is available within minutes.
  • Other tests usually take a few days.

In both instances, we contact you by telephone as soon as the results are available. A copy of the results are also sent to your gynaecologist immediately.

Do the chromosomal tests determine only Down syndrome?

  • The chromosomal analysis should confirm or exclude the possibility of Down syndrome and other chromosomal abnormalities. The baby’s gender is also confirmed by this test. (Please indicate whether you would like to know the baby’s gender!) Rarely, the following can happen:
  • A so-called chromosomal “mosaic” can be found. This means that some cells are normal, and others are abnormal. This can reflect the baby’s chromosomal pattern, but can result from abnormal cell development in the laboratory, in a baby with a normal chromosomal pattern. If a mosaic is found, it can be necessary to repeat the cordocentesis.
  • Chromosomal abnormalities of uncertain significance can be found. These include:
    • A translocation, where one part of a chromosome is found on another chromosome. This might have implications for the unborn baby, when he/she has children one day.
    • Chromosomal fractures, where the chromosomes break up in the cell culture. This might have implications for the health of the unborn baby as an adult.
    • Extra X or Y chromosomes. This might have implications for the unborn baby, when he/she has children one day.
    • The baby’s gender as seen on ultrasound, can differ from the gender as obtained by cordocentesis. This can mean that the sonar was wrong, that a sampling, culture or reporting error has slipped in, or that there is really a difference between the baby’s genetic and physical gender. It is important to determine this difference before the birth!

Which preparations should I take before the cordocentesis?

  • You do not need a full bladder. An empty bladder is less uncomfortable!
  • Bring someone along for moral support, and to drive you home afterwards.
  • Let us know if you have any bleeding tendency, or if you are using any medication (including low-dose aspirin or arnica).
  • Arrange to have the rest of the day off work. (Please let us know if we need to provide you with a sick note.)
  • Make sure whether your medical aid will refund the amniocentesis – both the amniocentesis itself, and the analyses in the biochemical and cytogenetical laboratories. Please note that you will receive two separate accounts for the amniocentesis: one by ourselves for the procedure, and one by the laboratory for the alpha feto protein, cell culture and karyotyping.  The laboratory fee will double for twins, triple for triplets etc.
  • If you are HIV positive, there is a potential risk of transferring the HIVirus to the baby with a cordocentesis. If you are HIV positive, or would like to be tested for HIV before the cordocentesis, please let us know beforehand.

Which precautions should I take after the cordocentesis?

  • Spend the rest of the day quietly at home. It is not necessary to stay in bed, but do not do physically strenuous work or exercise.
  • Do not pick up any heavy objects (including a toddler!) for the next two to three days.
  • Contact us or your doctor if any of the following should develop:
    • Abdominal pain or cramps worse than with a menstruation, and which do not respond to usual analgesics (one to two tablets paracetamol, e.g. Panado® of Dolorol®).
    • Vaginal bleeding
    • A watery vaginal discharge.
    • Fever or rigors
    • An offensive vaginal discharge
    • A decrease or cessation of fetal movements.


Chromosomal abnormalities