Diagnosing Trisomy 18

by | May 9, 2013 | Health Care

There are many different sorts of testing that can occur while you are pregnant to ensure that your developing baby is growing properly and will be born a happy, healthy baby. While pregnancy is an exciting time and most babies who are tested will have no genetic abnormalities or anything else similar to that, many parents choose to test just in case so they can prepare financially, mentally, and physically for a baby who might be born with a genetic defect. One thing that you may wish to consider, especially if Down syndrome is present in your family history, is a trisomy 18 screening. It is important to understand some aspects of this screening including what trisomy 18 screening is, how many babies are diagnosed with trisomy 18, and the symptoms associated with those who have trisomy 18.

Explaining Trisomy 18

Trisomy 18 screening allows doctors to determine if the developing baby has a chromosomal abnormality. This particular type of screening will check to find out if some of the cells have extra chromosome, in this case three copies of number 18 chromosome. There are three different types of trisomy 18 includes full trisomy, partial trisomy and mosaic. Full trisomy means that the extra chromosomes are found in every cell in the developing baby’s body and is the most common trisomy. In partial trisomy the baby does not have a full extra chromosome, instead they just have a partial extra chromosome that has attached to another chromosome in the cell. Finally, mosaic trisomy is where the extra chromosome is only present in some of the cells but not in all of them.

Occurrence of Diagnoses

The amount of babies who develop this form of trisomy varies depending on the time of pregnancy is tested. It is estimated that 1 in 5000 babies have this type of trisomy and most of these babies will be females. It is believed that this condition is more prevalent than the numbers show since most babies that have this defect will not survive to birth and instead die during the second trimester or the third trimester. This can be detected early with trisomy 18 screening.


There are a variety of symptoms that are present in babies born with trisomy 18. Most babies with this defect will be born frail and small unlike healthy babies who do not have this defect. On top of this they will suffer from other serious problems and defects from having trisomy 18 including heart defects, chest deformity, cleft palate, defects of the stomach, lungs, and kidneys, and slowed growth. It is important to provide all the proper screenings to test for this defect so that you can prepare for the challenges associated with having a child with trisomy 18.

If you would like to know more about Trisomy 18 Screening, contact Ariosa Diagnostics. They are available to answer your questions at 1-855-9-ARIOSA.

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