2010 Group Project 4
- 1 Percutaneous Umbilical Cord Blood Sampling
Percutaneous Umbilical Cord Blood Sampling
Percutaneous Umbilical Blood Sampling (PUBS) is an invasive pre-natal diagnostic procedure performed during the second trimester (between week 18 to 22) where a sample of fetal blood is extracted from the vein in the umbilical cord using a fine needle via the abdomen of the mother. The extracted blood can then be used to detect certain anomalies including chromosome abnormalities such as Down Syndrome, blood disorders such as Fetal Haemolytic Disease and intrauterine infection, growth retardation, and some birth defects as well as metabolic disorders. PUBS is often used when other diagnostic tests such as Ultrasound, Amniocentesis and Chorionic Villus Sampling do not yield conclusive results. This pre-natal diagnostic technique is also used to deliver certain therapies such as the administration of medicine and transfusion of blood directly to the fetus.
Although it is a very useful diagnostic technique, there are many complications associated with the procedure from haemorrhage and fetal bradycardia to premature birth and fetal death. The mortality rate associated directly to procedural factors has been found to be approximately 1 to 2 times out of every 100 procedures. The long list of associated risks have been found to be related to procedural factors such as duration and the number of punctures as well as individual circumstances of the patient for example gestational age.
Despite the risks involved, the one of the benefits of PUBS over that of other pre-natal diagnostic techniques such as Amniocentesis and Chorionic Villus Sampling (CVS), is that genetic information also known as Karyotypes is available much sooner after the procedure. This is especially important in cases requiring rapid diagnosis and/or management.
When is PUBS Preformed?
PUBS is usually preformed when other pre-natal diagnostic test such as Choronic Villi Sampling (CVS), Amniocentesis and Ultrasound do not yield conclusive results. PUBS is done during the second trimester or more precisely after week 18.
Percutaneous Umbilical Cord Sampling (PUBS) consists of three fundamental steps.
Step 1 - Imaging
An advanced imaging ultrasound is used to determine the location of where the umbilical cord inserts into the placenta. This ultrasound image is then used to guide a thin needle through the abdomen and uterine wall of the mother and into the the umbilical vein running through the cord.
Step 2 - Retrieval of Fetal Blood Sample
The needle is then inserted into the cord to retrieve a small sample of fetal blood. There are two main routes for the retrieval of fetal blood. The method used to perform the procedure is determined by the position of the placenta in the uterus and point of connection with the umbilical cord.
(i) Placenta Anterior (where the placenta is attached towards the front of the uterus) - the needle is inserted straight into the umbilical cord without penetrating the amniotic sac. The amniotic sac is a fluid–filled structure that surrounds the developing fetus acting as a cushion thus protecting it.
(ii) Placenta Posterior (where the placenta is attached towards the back of the uterus) - the needle must travel through the amniotic sac to reach the umbilical cord. This may cause some temporary bleeding and cramps.
It is also important to note when performing cordocentesis, if the mother is Rh–negative, Rh Immune-Globulin (RhIG) is administered to the mother in order to prevent the development of Rh incompatibility.
Step 3 - Sample Analysis
The fetal blood sample is sent to a lab where it is screened for genetic defects and other disorders. The results for the test are usually available within 72 hours however under some circumstances, may take a few weeks to obtain the results. In the event of diagnosis, implementation of the most suitable procedure for management of the condition occurs or in extreme cases, the pregnancy is terminated.
Disorders and Abnormalities Found by PUBS
Percutaneous Umbilical Blood Sampling also known as Cordocentesis like stated above is a pre-natal diagnostic test that is usually preformed to detect abnormalities such as Trisomy 21 (Down Syndrome) and Trisomy 18 (Edwards Disease) and blood disorders for example Fetal Hemolytic Disease. Yet on the whole Cordocentesis may be performed to help diagnose any of the concerns listed below:
• Fetal anemia
• Malfunction of the fetus
• Fetal platelet count of the mother
• Fetal infections like rubella or toxoplasmosis
• Respiratory illnesses
• Congenital heart defects
Yet one major disadvantage when comparing Percutaneous Umbilical Blood Sampling to other major testing method for example Choronic Villi Sampling (CVS) and Amniocentesis is that PUBS does not help test for neural tube defects such as Spina Bifida
Associated Risk and Complications
Similarities and Differences to other Pre-natal Diagnostic Technique
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2010 ANAT2341 Group Projects
Project 1 - Ultrasound | Project 2 - Chorionic villus sampling | Project 3 - Amniocentesis | Group Project 4 - Percutaneous Umbilical Cord Blood Sampling | Project 5 - Fetal Fibronectin | Project 6 - Maternal serum alpha-fetoprotein | Group Assessment Criteria
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Cite this page: Hill, M.A. (2020, June 4) Embryology 2010 Group Project 4. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_Group_Project_4
- © Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G