Fetal blood sampling (FBS) is the technique used to collect a small amount of blood from the umbilical cord to allow it to be sent to the laboratory for testing. FBS is used to detect Down Syndrome and most other chromosome abnormalities in the fetuses of couples who are at increased risk of having an affected child. In addition, many other diseases that can be diagnosed in adults, can also be diagnosed in fetuses using this technique.

FBS is an out-patient procedure carried out after 18 weeks of pregnancy. Partners are welcome to attend. It takes about 30 minutes in all and no special preparation is needed. Most of this time is spent being scanned and preparing equipment; it takes about 2 or 3 minutes to obtain the sample of fetal blood. You will need to know your blood group and if it is rhesus negative, you will receive an injection after the procedure. Your Consultant will explain why this is necessary. First, ultrasound will be used to determine the position of the fetus, the placenta and the umbilical cord.

The blood sample is sent to the CGS laboratory in London for testing, the chromosome tests can usually be completed in two to four working days. The sex of the fetus will be revealed by the chromosome test and parents can choose whether or not they wish to have this information. Fetal blood sampling is the most accurate technique available for predicting the fetal chromosomes, about one in one hundred (1%) pregnancies will miscarry as a result of fetal blood sampling.

If the fetus is shown to have an abnormality you will be told what the problem means for a baby and what treatment is available. You and your partner can then decide whether or not you wish to continue the pregnancy. Couples considering fetal blood sampling should decide early on whether or not they feel they could accept termination of pregnancy. If they do not, all that testing can provide is advance knowledge that the baby does or does not have a specific abnormality.

Patient procedure notes:

• A patch of skin on the abdomen will be cleaned with antiseptic and local anaesthetic injected to numb the area.
  

• A fine needle will be guided through the mother’s abdomen into the amniotic fluid and then the umbilical cord. The movement of the needle will be checked by ultrasound throughout the procedure and you may be able to watch what is happening on the video screen.
  

• Because the umbilical cord is extremely small in early pregnancy it may take a few minutes to locate it accurately.
  

• A small volume of fetal blood will be collected and the needle will be withdrawn. You will be asked to rest at home for the remainder of the day and to avoid vigorous exercise for two more days.