Patau Syndrome can be detected prenatally (before birth) through a range of different tests that the mother can undertake.
These different tests can be broken into two different groups:[1]
SCREENING TESTS
There are two major forms of screening tests with each of these tests being undertaken during the first or second trimester of pregnancy.
Combined Screening Tests
First trimester combined screening tests are undertaken during the 11th - 13th week of gestation. These tests involve the mother undertaking a blood test, which is used to measure the levels of two different proteins that appear in her blood during pregnancy.[2] These proteins are pregnancy-associated plasma protein-A and human chorionic gonadotropin.[3]
The information gathered from these blood tests is then combined with the visual signs that an ultrasound shows in order to determine if the child is at a higher risk of Down Syndrome (Trisomy 21) or Edwards Syndrome (Trisomy 18).[2] However, these tests also provide evidence regarding the risk of Neural Tube Defects which are common within sufferers of Patau Syndrome.
Maternal Serum Screening
The other major form of prenatal screening test can be undergone during the second trimester, during the 15th - 17th week of gestation. Maternal Serum Screening involves another blood test taken from the mothers arm (shown in figure 3.1)[4], however this test is used to detect the levels of four different proteins within the mother's blood stream that are made by the baby or the placenta.[2] These proteins are Alpha-fetoprotein (made by the baby's liver), Human Chorionic Gonadotropin (made by the placenta), Unconjugated Estriol (made by the baby's liver and the placenta), and Dimeric Inhibin A (made by the placenta).[5]
The levels of these proteins are then combined with information about the mother (specifically age) in order to gauge the risk of the child being born with a birth defect.
Those that show an increased risk in either of these screening tests should then be offered a form of diagnostic test in order to accurately diagnose the child.
These different tests can be broken into two different groups:[1]
- Screening tests - These tests explains the risk of your child having a birth defect (such as trisomy 13)
- Diagnostic tests - These tests examine the childs genetic material in order to accurately diagnose the defect
SCREENING TESTS
There are two major forms of screening tests with each of these tests being undertaken during the first or second trimester of pregnancy.
Combined Screening Tests
First trimester combined screening tests are undertaken during the 11th - 13th week of gestation. These tests involve the mother undertaking a blood test, which is used to measure the levels of two different proteins that appear in her blood during pregnancy.[2] These proteins are pregnancy-associated plasma protein-A and human chorionic gonadotropin.[3]
The information gathered from these blood tests is then combined with the visual signs that an ultrasound shows in order to determine if the child is at a higher risk of Down Syndrome (Trisomy 21) or Edwards Syndrome (Trisomy 18).[2] However, these tests also provide evidence regarding the risk of Neural Tube Defects which are common within sufferers of Patau Syndrome.
Maternal Serum Screening
The other major form of prenatal screening test can be undergone during the second trimester, during the 15th - 17th week of gestation. Maternal Serum Screening involves another blood test taken from the mothers arm (shown in figure 3.1)[4], however this test is used to detect the levels of four different proteins within the mother's blood stream that are made by the baby or the placenta.[2] These proteins are Alpha-fetoprotein (made by the baby's liver), Human Chorionic Gonadotropin (made by the placenta), Unconjugated Estriol (made by the baby's liver and the placenta), and Dimeric Inhibin A (made by the placenta).[5]
The levels of these proteins are then combined with information about the mother (specifically age) in order to gauge the risk of the child being born with a birth defect.
Those that show an increased risk in either of these screening tests should then be offered a form of diagnostic test in order to accurately diagnose the child.
DIAGNOSTIC TESTS
Once the mother has been recommended on to a diagnostic test due to the higher then average risk of the child being born with a birth defect she can undertake one of the following three major diagnostic tests. Amniocentesis Amniocentesis can be undertaken from the 15th to the 18th week of gestation and it is the process in which a hollow needle is inserted into the uterus through the abdomen and into the amniotic sac in order to extract a small amount (less then one ounce) of amniotic fluid. The needle is guided through the use of ultrasound imaging in order to avoid damaging the foetus (shown figure 3.2).[6][7] However, this procedure brings with it its own risk. Less then 1% or between 1 in 300 and 1 in 500 people that have undergone this procedure have experienced a miscarriage as a direct result of this procedure.[8] On the other hand however, Amniocentesis can be used to identify chromosomal abnormalities, genetic disorders, and neural tube defects.[7] Transabdominal Chorionic Villus Sampling The process Transabdominal Chorionic Villus Sampling can be undertaken anywhere from the 10th to the 19th week of gestation.[9] This procedure is used to extract a tissue sample from the chorionic villi located in the placenta (shown figure 3.3)[10] by inserting a thin needle through the abdomen and guided by ultrasound imaging. The tissue sample that is extracted is then sent off to a laboratory where it undergoes a process called Polymerase Chain Reaction (PCR). PCR is used to count the number of chromosome present within the cells gathered from the placenta, this number should equal 23 pairs or 46 individual chromosomes. However, if the total number of chromosomes is either more or less then 46 then the cells undergo a full karyotyping. This karyotyping allows for the identification of exactly what abnormality is present (eg. Patau Syndrome).[11] However, this procedure also carries the risk of miscarriage in that 1% (1 in 100) of those that undergo this procedure experience a miscarriage.[9] The benefit to this procedure is that the early timing of these tests allow the parents enough time to ponder their circumstances and the risks involved in carrying this child to full-term. Detailed Fetal Ultrasound A detailed fetal ultrasound, also called a foetal morphology or anomaly scan, is performed between the 18th and 20th week of pregnancy. At this stage of the pregnancy the foetus will be large enough to distinguish body structure and development.[12] During this scan the sonographer will inspect the images shown by the ultrasound devices in order to examine the:[13]
One of the major benefits of ultrasound testing is also the fact that it utilises a safe procedure by using low-energy sound waves to map an image of the child[14] (shown figure 3.4).[15] |
REFERENCE LIST:
[1] The Royal Women's Hospital, (n.d.). Genetic testing in pregnancy. [online] Available at: https://www.thewomens.org.au/health-information/pregnancy-and-birth/now-you-are-pregnant/genetic-testing-in-pregnancy/ [Accessed 16 Aug. 2014].
[2] Better Health Channel, (2014). Maternal serum screening. [online] Available at: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Maternal_serum_screening [Accessed 16 Aug. 2014].
[3] Mayo Clinic, (2012). First Trimester Screening. [online] Available at: http://www.mayoclinic.org/tests-procedures/first-trimester-screening/basics/definition/prc-20014597 [Accessed 16 Aug. 2014].
[4] Doctor Tipster, (n.d.). Biochemical Screening. [image] Available at: http://www.doctortipster.com/wp-content/uploads/2012/04/Biochemical-Screening.jpg [Accessed 16 Aug. 2014].
[5] Emory University School of Medicine, (2008). About Maternal Serum Screening. [online] Available at: http://genetics.emory.edu/docs/Emory_Human_Genetics_About_Maternal_Serum_Screening.pdf [Accessed 16 Aug. 2014].
[6] Amniocentesis. (n.d.). [image] Available at: http://www.stanfordchildrens.org/content-public/topic/images/85/161385.gif [Accessed 16 Aug. 2014].
[7] American Pregnancy Association, (2014). Amniocentesis. [online] Available at: http://americanpregnancy.org/prenataltesting/amniocentesis.html [Accessed 16 Aug. 2014].
[8] Mayo Clinic, (2012). Amniocentesis. [online] Available at: http://www.mayoclinic.org/tests-procedures/amniocentesis/basics/risks/prc-20014529 [Accessed 16 Aug. 2014].
[9] Better Health Channel, (2012). Pregnancy Tests - Chorionic Villus Sampling. [online] Available at: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/pregnancy_tests_chorionic_villus_sampling [Accessed 17 Aug. 2014].
[10] Chorionic Villi. (n.d.). [image] Available at: http://umm.edu/~/media/ADAM/Images/en/19163.ashx [Accessed 16 Aug. 2014].
[11] BabyCentre, (2011). Chorionic villus sampling (CVS). [online] Available at: http://www.babycentre.co.uk/a328/chorionic-villus-sampling-cvs [Accessed 16 Aug. 2014].
[12] Puhja, M. (n.d.). 18-20 week screening pregnancy ultrasound. [online] Inside Radiology. Available at: http://www.insideradiology.com.au/pages/view.php?T_id=68#.U_ATbYCSxuA [Accessed 17 Aug. 2014].
[13] BabyCenter, (2014). 18 - 20 week pregnancy ultrasound. [online] Available at: http://www.babycenter.com.au/a557390/18---20-week-pregnancy-ultrasound [Accessed 17 Aug. 2014].
[14] Mayo Clinic, (2012). Ultrasound Risks. [online] Available at: http://www.mayoclinic.org/tests-procedures/ultrasound/basics/risks/prc-20020341 [Accessed 17 Aug. 2014].
[15] Ultrasound. (n.d.). [image] Available at: http://members.shaw.ca/rr.burak/Ch04/ultrasound.jpg [Accessed 17 Aug. 2014].
[1] The Royal Women's Hospital, (n.d.). Genetic testing in pregnancy. [online] Available at: https://www.thewomens.org.au/health-information/pregnancy-and-birth/now-you-are-pregnant/genetic-testing-in-pregnancy/ [Accessed 16 Aug. 2014].
[2] Better Health Channel, (2014). Maternal serum screening. [online] Available at: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Maternal_serum_screening [Accessed 16 Aug. 2014].
[3] Mayo Clinic, (2012). First Trimester Screening. [online] Available at: http://www.mayoclinic.org/tests-procedures/first-trimester-screening/basics/definition/prc-20014597 [Accessed 16 Aug. 2014].
[4] Doctor Tipster, (n.d.). Biochemical Screening. [image] Available at: http://www.doctortipster.com/wp-content/uploads/2012/04/Biochemical-Screening.jpg [Accessed 16 Aug. 2014].
[5] Emory University School of Medicine, (2008). About Maternal Serum Screening. [online] Available at: http://genetics.emory.edu/docs/Emory_Human_Genetics_About_Maternal_Serum_Screening.pdf [Accessed 16 Aug. 2014].
[6] Amniocentesis. (n.d.). [image] Available at: http://www.stanfordchildrens.org/content-public/topic/images/85/161385.gif [Accessed 16 Aug. 2014].
[7] American Pregnancy Association, (2014). Amniocentesis. [online] Available at: http://americanpregnancy.org/prenataltesting/amniocentesis.html [Accessed 16 Aug. 2014].
[8] Mayo Clinic, (2012). Amniocentesis. [online] Available at: http://www.mayoclinic.org/tests-procedures/amniocentesis/basics/risks/prc-20014529 [Accessed 16 Aug. 2014].
[9] Better Health Channel, (2012). Pregnancy Tests - Chorionic Villus Sampling. [online] Available at: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/pregnancy_tests_chorionic_villus_sampling [Accessed 17 Aug. 2014].
[10] Chorionic Villi. (n.d.). [image] Available at: http://umm.edu/~/media/ADAM/Images/en/19163.ashx [Accessed 16 Aug. 2014].
[11] BabyCentre, (2011). Chorionic villus sampling (CVS). [online] Available at: http://www.babycentre.co.uk/a328/chorionic-villus-sampling-cvs [Accessed 16 Aug. 2014].
[12] Puhja, M. (n.d.). 18-20 week screening pregnancy ultrasound. [online] Inside Radiology. Available at: http://www.insideradiology.com.au/pages/view.php?T_id=68#.U_ATbYCSxuA [Accessed 17 Aug. 2014].
[13] BabyCenter, (2014). 18 - 20 week pregnancy ultrasound. [online] Available at: http://www.babycenter.com.au/a557390/18---20-week-pregnancy-ultrasound [Accessed 17 Aug. 2014].
[14] Mayo Clinic, (2012). Ultrasound Risks. [online] Available at: http://www.mayoclinic.org/tests-procedures/ultrasound/basics/risks/prc-20020341 [Accessed 17 Aug. 2014].
[15] Ultrasound. (n.d.). [image] Available at: http://members.shaw.ca/rr.burak/Ch04/ultrasound.jpg [Accessed 17 Aug. 2014].