How is Edwards Detected?
Trisomy 18 is detected in two steps. These two steps are a Screening test, and a Diagnosis test. The first set of tests is a screening test. The screening test is done to check the likeliness/risk of the child having trisomy 18. The screening test is made up of two different types of tests [4]. The first is an AFP test (Triple Test), which is a Maternal blood test which is looking for the three substances AFP, hCG, and Estriol which is usually done between the 15 week and 17 week mark and is still accurate through 20 weeks. It can also be done in rare cases as late as 22 weeks. From the results gathered, a risk assessment will be done that will compare the results that you have given against every other test that has been done in order to see what chance your child has of having Trisomy 18[5]. If the likelihood is high, you will then have a level 2 ultrasound (targeted ultrasound). In this scan, the child will be looked at to see if it has any soft markers (Characteristics that are most commonly seen on babies with Trisomy 18) and structural markers (Abnormalities in Bone and Organ Structure). [6]
If is believed that the child has Trisomy 18, a diagnostic test will be done. There are two different diagnostic tests that can be performed. The first is called a CVS (Chorionic Villi Sampling). This is done by taking Chorionic Villi (Small amounts of tissue that connect the pregnancy sac to the uterus wall) and checking the chromosomal structure of it's cells. This is done because it usually has the same genetic make up as the child it carries. It is performed 10-12 weeks after the mothers last menstrual period and has the advantage of early detection/diagnosis, however it does come with a small risk of Miscarriage and is therefore not offered to all pregnant women. [7]
The second diagnostic test is Amniocentesis. Although this isn't usually performed until 15 weeks and loses out on early detection, it has a slightly smaller chance of miscarriage than CVS. This is done by removing a very small amount of the Amniotic Fluid from the amniotic sac with a very fine needle. This is then sent off to a laboratory for analysis. This usually takes 10 days or more, however there is a quicker version called a FISH test which creates a Karyotype of the baby's genes. This will clearly show wether or not the baby has Trisomy 18 or not. However, with a FISH test, Adobe Acrobat Reader has to be installed (this test has been designed to work with the free version of this application).[8]
If this tests show that the child has Edwards Syndrome, a lot of big decisions have to be made.
If is believed that the child has Trisomy 18, a diagnostic test will be done. There are two different diagnostic tests that can be performed. The first is called a CVS (Chorionic Villi Sampling). This is done by taking Chorionic Villi (Small amounts of tissue that connect the pregnancy sac to the uterus wall) and checking the chromosomal structure of it's cells. This is done because it usually has the same genetic make up as the child it carries. It is performed 10-12 weeks after the mothers last menstrual period and has the advantage of early detection/diagnosis, however it does come with a small risk of Miscarriage and is therefore not offered to all pregnant women. [7]
The second diagnostic test is Amniocentesis. Although this isn't usually performed until 15 weeks and loses out on early detection, it has a slightly smaller chance of miscarriage than CVS. This is done by removing a very small amount of the Amniotic Fluid from the amniotic sac with a very fine needle. This is then sent off to a laboratory for analysis. This usually takes 10 days or more, however there is a quicker version called a FISH test which creates a Karyotype of the baby's genes. This will clearly show wether or not the baby has Trisomy 18 or not. However, with a FISH test, Adobe Acrobat Reader has to be installed (this test has been designed to work with the free version of this application).[8]
If this tests show that the child has Edwards Syndrome, a lot of big decisions have to be made.
[3] . 2014. . [ONLINE] Available at: http://medgen.genetics.utah.edu/photographs/diseases/high/cytog003.jpg. [Accessed 14 August 2014].
[4] How Trisomy 18 is Diagnosed - Trisomy 18 Foundation . 2014. How Trisomy 18 is Diagnosed - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_diagnosing. [Accessed 14 August 2014].
[5] AFP Testing - Trisomy 18 Foundation . 2014. AFP Testing - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_afp. [Accessed 14 August 2014].
[6] Level 2 Ultrasound - Trisomy 18 Foundation . 2014. Level 2 Ultrasound - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_us. [Accessed 14 August 2014].
[7] Chorionic Villi Sampling - Trisomy 18 Foundation . 2014. Chorionic Villi Sampling - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_cvs. [Accessed 14 August 2014].
[8] Amniocentesis - Trisomy 18 Foundation . 2014. Amniocentesis - Trisomy 14 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_amnio. [Accessed 14 August 2014].
[4] How Trisomy 18 is Diagnosed - Trisomy 18 Foundation . 2014. How Trisomy 18 is Diagnosed - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_diagnosing. [Accessed 14 August 2014].
[5] AFP Testing - Trisomy 18 Foundation . 2014. AFP Testing - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_afp. [Accessed 14 August 2014].
[6] Level 2 Ultrasound - Trisomy 18 Foundation . 2014. Level 2 Ultrasound - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_us. [Accessed 14 August 2014].
[7] Chorionic Villi Sampling - Trisomy 18 Foundation . 2014. Chorionic Villi Sampling - Trisomy 18 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_cvs. [Accessed 14 August 2014].
[8] Amniocentesis - Trisomy 18 Foundation . 2014. Amniocentesis - Trisomy 14 Foundation . [ONLINE] Available at: http://www.trisomy18.org/site/PageServer?pagename=whatis_amnio. [Accessed 14 August 2014].