The Presence of Trisomies: What Does it Mean for Your Unborn Child?

Many parents meet the risk factors that doctors commonly review to determine whether or not prenatal DNA testing is needed. Some of these factors include advanced age (35 years or older), a familial history of genetic defects, a positive serum screen and/or ultrasound findings. Mothers who meet any or all of these criteria are often sent for additional testing for the presence of certain trisomies.

A healthy child has a total of 23 pairs of chromosomes. Trisomies occur when one of these pairs are copied, either partially or completely. There are three more common trisomies, and they are trisomy 21, trisomy 18, and trisomy 13.

Trisomy 21 (Down syndrome)


Trisomy 21 is characterized by common physical signs such as decreased muscle tone, flattened nose, small ears and mouth, upward slanting eyes, and physical growth delays. In addition, mild to moderate intellectual disability is present, with the average IQ of an affected young adult hovering near 50. In spite of this intellectual disability, most children with Down syndrome are usually incredibly happy individuals leading relatively high functioning lifestyles. Some adults even go on to attend college, live on their own, and take on paid work in some capacity. The average lifespan is approximately 50 to 60 years of age, which is 15 to 25 years shorter than average, but still relatively high.

Unfortunately, health complications are common in individuals with trisomy 21. Congenital heart defects, gastrointestinal disorders, and disorders of the endocrine system are the most common.

Trisomy 18 (Edwards syndrome)


Trisomy 18 occurs when the chromosomal copy is created in the 18th pair of chromosomes. This condition often includes organ abnormalities, heart defects, an abnormally shaped head, and clenched fist with overlapping fingers. Due to the presence of severe medical problems in those affected with trisomy 18, most die before birth or within the first month. Those that survive the first month will typically die within the first year.

Trisomy 13 (Patau syndrome)

Much like Trisomy 18, Trisomy 13 also causes high infant mortality and low survival rates for those that survive after birth. Those affected by trisomy 13 typically have brain or spinal cord abnormalities, poorly developed eyes (microphthalmia), and weak muscle tone (hypotonia).

What can you do?

While you can’t prevent a genetic abnormality, you can be proactive. Your doctor may order a cell-free DNA test that will test for the presence of these trisomies. Results are typically available in your healthcare professional’s office in 5 days after the lab receives the original blood sample, and can help you and your partner better determine how to plan for your future family.

While the occurrence of trisomies shouldn’t discourage you from having children, it should encourage you to discuss risk factors as well as testing methods with your healthcare professional.


Article Submitted By Derrick Manning (Community Writer)

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