2010 Group Project 4

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Percutaneous Umbilical Cord Blood Sampling

Introduction

Schematic of placental circulation and location of umbilical vein

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 umbilical 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.

History

Procedure

When is PUBS Performed?


PUBS is an invasive procedure and as a result, it carries with it a relatively high risk of complications. Therefore, it is generally to be used in the case of high-risk pregnancies. A high-risk pregnancy is classified as such due to various factors that indicate a significantly increased likelihood of genetic defects. These may include:

- An advanced maternal age of 35 and over

- A previous pregnancy affected with chromosomal disorder

- Family history of genetic disorders (E.g. monogenic disease carrier status or balanced chromosomal translocation in a parent, history of X-linked or inborn metabolic disorders etc.)

- Abnormal results identified on a previously performed non-invasive procedure, such as ultrasound or maternal serum biochemistry screening [1]


PUBS in comparison with other diagnostic techniques

PUBS is usually performed after non-invasive procedures such as ultrasound and biochemical markers, have indicated the possibility of genetic disorders. Because, these tests generally produce highly sensitive results, they are not always reliable at giving an accurate diagnosis. Therefore, an invasive technique such as PUBS is employed to in an attempt to provide more conclusive and accurate information.[2]

PUBS may also be used when other invasive pre-natal diagnostic tests including chorionic villi sampling (CVS) and amniocentesis do not yield conclusive results. These methods are similar in that they involve the examination of cell samples obtained directly from the developing fetal structures.


PUBS Chorionic Villi Sampling Amniocentesis
risk of complications 1-2% 2% 0.5-1%
recommended time period for testing 18-23 weeks 8-11 weeks 16-18 weeks
available diagnostic analyses karyotype and DNA analysis, biochemical studies, detection of blood disorders and intrauterine infections. unable to detect neural tube defects. karyotype and DNA analysis, enzyme studies. least accurate in cytogenic analysis. karyotype and DNA analysis, biochemical studies
time taken for samples to be cultured 72 hours 9-10 days 10-11 days

[3] [4]

Advantages of PUBS:

- Accurate at detecting the presence of genetic disorders

- Sample is available for many different types of analysis, which allows for the detection of a wide range of defects

- Results are available relatively soon after procedure has taken place


Disadvantages of PUBS:

- Unable to accurately detect the severity of disorders

- Takes place only later in pregnancy

- Recognised as posing potential risks

- Unable to detect neural tube defects





Percutaneous Umbilical Cord Sampling (PUBS) is the performed by the advancement of a needle within a ultrasound visual field to a targeted puncture site and 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 throughout the procedure in order 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. The ideal sample site for PUBS is located at the root of the umbilical cord due to its stable fixed position which is less susceptible to disturbances caused by fetal movement compared to the free loops of the cord.


Placenta Anterior Placenta Posterior
Description Placenta attached to anterior wall of uterus - the needle is inserted straight into the umbilical cord without penetrating the amnion and amniotic cavity Placenta located on posterior wall of uterus - the needle must travel through the amniotic sac to reach the umbilical cord. This may cause some temporary bleeding and cramps
Diagram
Placenta Anterior
Placenta Posterior


There are two techniques that can be used when obtaining the sample: freehand and needle-guided. The choice of technique is dependent on a number of factors including the location of the cord root and the preferences of the physician performing the procedure.

1. Freehand - allows lateral readjustment of needle direction once within the uterus. A transducer is used to navigate the needle to the specific sample site and is the more preferred technique due to the increased range of movement

2. Needle-guided - involves the insertion of a separate needle straight into the targeted puncture site with the aid of the transducer, which forms a fixed passage through with a second smaller needle passes to retrieve the fetal blood. Despite permitting precise alignment of the needle tract with the vessel, the range of movement is limited to a single plane of travel [5]

Doppler image of needle-guided technique


It is also important to note when performing PUBS, that if the mother is Rh–negative, Rh Immune-Globulin (RhIG) is administered to the mother in order to prevent the development of Rh incompatibility and further sensitization.


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

• Isoimmunisation

• 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

Useful Links

Search Bookshelf Percutaeous Umbilical Cord Sampling

Search Pubmed Now: Percutaeous Umbilical Cord Sampling


References

  1. <pubmed>18292841</pubmed>
  2. <pubmed>8907774</pubmed>
  3. <pubmed>18292841</pubmed>
  4. <pubmed>20193481</pubmed>
  5. <pubmed>8739583</pubmed>

Glossary

Amnion: An extraembryonic membrane ectoderm and extraembryonic mesoderm in origin and forms the innermost fetal membrane, produces amniotic fluid.

Amniotic Cavity: The fluid-filled (amniotic fluid) extraembryonic coelom (cavity) formed initially by epiblast and then ectoderm and surrounding extraembryonic mesoderm. In humans, it forms the innermost fetal membrane, produces amniotic fluid expanding to fuse with the chorionic membrane during week 8 of development.

Ultrasound: A non-invasive technique for visualizing and prenatal diagnosis of several features of development including: follicles in the ovaries, the gestational sac, fetus in the uterus, fetal parameters, and the placenta. The technique uses high-frequency sound waves that are reflected off internal structures.

Umbilical Cord: (placental cord) The placental cord is the structure connecting the embryo/fetus to the placenta. It is initially extra-embryonic mesoderm forming the connecting stalk within which the placental blood vessels (arteries and veins) form. In human placental cords the placental blood vessels are initially paired, later in development only a single placental vein remains with a pair of placental arteries. This structure also contains the allantois, an extension from the hindgut cloaca then urogenital sinus. Blood collected from the placental cord following delivery is a source of cord blood stem cells.


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. (2019, December 6) Embryology 2010 Group Project 4. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_Group_Project_4

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G