Trisomy 18 is a genetic chromosomal disorder characterized by an extra chromosome that causes abnormalities in various parts of the body. Also known as Edwards’ syndrome, it is the second most common trisomy behind Trisomy 21 (Down Syndrome).
Trisomy 18 occurs when chromosome cells fail to properly divide during gestation. Usually, the chromosomes that make up your body come in sets of two, with a healthy genome being made up of 23 pairs. In cases of trisomy 18, a person develops a third chromosome in the 18th pair. The extra chromosome, which will be present in every cell in the body, causes severe and often fatal birth defects.
Three types of trisomy can occur:
Trisomy 18 is usually diagnosed by a health care professional prenatally, in other words, while the baby is still in the womb. However, the process of testing for the condition is the same whether it is done before or after birth. To test for trisomy 18, a DNA sample is extracted from either the baby’s blood or body tissue and cultured so that the doctor can examine a picture of the chromosomes known as a karyotype.
To successfully obtain a karyotype of the baby’s DNA, the chromosomes are isolated, stained, and then examined under a microscope that can then take a photo to be examined. This karyotype should be able to show your doctor if there is indeed a third, extra chromosome 18 present in your baby’s cells.
Another common method of testing for trisomy 18 and other types of abnormalities is a maternal serum screening, also known as a multiple marker test. This prenatal screening is administered either during the first trimester (a Combined First Trimester Screening, or “CFTS”), or during the second trimester (a Second Trimester Maternal Serum Screening, or “2TMSS”).
These screenings measure several substances in a pregnant woman’s blood. With this information, doctors can estimate the chance that the pregnancy will be affected by a chromosomal condition or certain other developmental problems by separating women in to “high chance” or “low chance” categories.
Trisomy 18 is often suspected during pregnancy from a blood test or ultrasound imaging. But a blood test or ultrasound is not a path to a confident diagnosis. There is also a Non-Invasive Prenatal Test (NIPT) that will tell you, usually within 10 days, a great deal more about your relative risk of having a child with Down syndrome or trisomy 18. But even that test is not definitive. The only definitive test is an amniocentesis. The downside of this test is there is a 1 in 200 chance of pregnancy loss from the test which involves putting a fine needle in your belly to extract amniotic fluid.
It is hard to talk about life expectancy with trisomy 18. It is just very sad. Most children do not survive their first month. For infants who survive the first month of life, 36% survived at age 1. Only ten percent of children with trisomy 18 survive to age 10.
Edwards Syndrome is another name for trisomy 18.
Most cases of trisomy 18 are not hereditary. This is no one’s fault. Parents who have a child with trisomy 18 do, however, have a greater risk of having another child with this chromosomal abnormality.
Much like Down syndrome, the effects of trisomy 18 can range from mild to severe, meaning that it will manifest in every child differently. No matter how mild or severe the case may be, the presence of trisomy 18 causes a host of problems.
Common problems associated with Trisomy 18 include:
Unfortunately, studies show that there is a very high mortality rate associated with the condition. The average lifespan for infants that are born with this condition is between 3 days – 2 weeks. Studies have shown a 5-10% chance of surviving the first year.
Due to this, most care for babies born with Edwards’s syndrome is more focused on palliative care and optimizing quality of life. Treatment for complications varies depending on the affected organ and severity of the condition. The management of Edward’s syndrome will depend entirely on the severity of symptoms present in the child.
Sadly, a diagnosis of trisomy 18 means that you as a parent will be faced with some extremely difficult decisions regarding the care of your baby. There are many resources available to help you in this process, from intervention services, hospice care, social workers, and genetic counselors. There are also many support groups created for families that are dealing with the same problems, which are excellent sources of support as you work to cope with this diagnosis.