Trisomy 18 or Edwards’ syndrome is a genetic disorder in which a child has three copies of chromosome 18 instead of two. Babies born with trisomy 18 have heart, brain, spinal cord and other birth defects. Mortality is very high in trisomy 18; most babies die before birth or by the age of 1 year.
Almost 1 in 5000 babies in the world are born with trisomy 18 and most of them are females. Incidence of Trisomy 18 increases with maternal age. Children with trisomy 18 have slow growth before birth (intrauterine growth retardation) and have a low birth weight.
Children with trisomy 18 are very weak and small. They may exhibit some signs such as
- Distinct facial features such as small head, small jaw short neck and deformed ears
- Deformities-Clubfoot or cleft palate
- Clenched fists with overlapping fingers
- Developmental delay
- Feeding problems
- Chest deformation
- Heart septal defects
- Lung, kidneys and intestinal defects
Maternal marker screening: It includes a series of tests done in the second trimester to evaluate a woman’s risk of carrying a baby with chromosomal anomalies. It includes- double marker test, triple marker tests and quadruple marker test. These tests are done usually between 15-20 weeks of pregnancy. The Double marker test assesses the levels of the human chorionic gonadotropin and Pregnancy Associated Plasma Protein. The levels of these components help to detect Edwards’ syndrome.
If screening test results are positive, then the following diagnostic tests are done to confirm that the fetus has trisomy 18.
- Chorionic villus sampling: It is done during first trimester between 10 to 13 weeks of pregnancy. In this test, a small sample of tissue from chorionic villi(a part of the placenta) is taken. The genetic material in the cells of these chorionic villi is the same as that of the developing fetus. Genetic testing of this sample is done to find out if the fetus has Edwards’ syndrome. This procedure has a low risk of miscarriage.
- Amniocentesis: It is done during second trimester after 15 weeks of pregnancy. Amniotic fluid contains cells of the baby which are shed during development. In this procedure, a sample of the amniotic fluid is taken and is tested for abnormality in the chromosomes in the cells of the fetus. This procedure also has low risk of miscarriage.
- Percutaneous Umbilical Cord Blood Sampling: It is done during second trimester after 17 weeks of pregnancy. Fetal blood is retrieved from the umbilical cord and a chromosomal analysis is done.
Diagnostic tests after pregnancy: Edwards’ syndrome can be detected at birth based on the facial and bodily features of the baby. However, a chromosomal analysis of the baby blood is required to confirm Edwards’ syndrome.
There is no cure for trisomy 18. Supportive medical care may be useful to improve the quality of life of the child.
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- What Is Trisomy 18?. https://www.webmd.com/baby/what-is-trisomy-18#2. Accessed on 27-Oct-2017.
- Anna Cereda and John C Carey. The trisomy 18 syndrome. Orphanet J Rare Dis. 2012; 7: 81.
- Trisomy 18 and 13. http://www.stanfordchildrens.org/en/topic/default?id=trisomy-18-and-13-90-P02419. Accessed on 27-Oct-2017.
- Edwards syndrome. https://en.wikipedia.org/wiki/Edwards_syndrome. Accessed on 27-Oct-2017. Accessed on 27-Oct-2017.
- Trisomy 18 Syndrome. http://www.dovemed.com/diseases-conditions/trisomy-18-syndrome/. Accessed on 27-Oct-2017.
- http://www.metropolisindia.com/wpcontent/uploads/2016/08/Maternal_Screening_Tests.pdf. Accessed on 27-Oct-2017.
- Trisomy18(EdwardsSyndrome). http://www.aboutkidshealth.ca/En/HealthAZ/ConditionsandDiseases/GeneticDisorders/Pages/trisomy-18-edwards-syndrome.aspx. Accessed on 27-Oct-2017.
- Percutaneous Umbilical Cord Blood Sampling. https://embryology.med.unsw.edu.au/embryology/index.php/2010_Group_Project_4. Accessed on 27-Oct-2017.
- Edwards Syndrome (Trisomy 18). https://www.nhs.uk/conditions/edwards-syndrome/Pages/Introduction.aspx. Accessed on 27-Oct-2017.