The US Centers for Disease Control and Prevention (CDC) say that birth defects affect 1 in every 33 babies, or about 3% of the population. One of the most common birth defects is a chromosomal condition known as trisomy. There are several types of trisomy. The most common are Down syndrome, Patau syndrome, and Edwards’ syndrome.
What is trisomy?
Trisomy is a scientific term used to describe cells with three copies of a chromosome. When a baby is conceived, healthy sperm and egg cells have 23 chromosomes each. After the sperm fertilizes the egg, a baby receives a complete set of 46 chromosomes.
Sometimes, errors occur as the chromosomes divide in half. For example, a sperm or egg cell may keep both copies of a particular chromosome instead of just one. If this egg or sperm becomes fertilized, then the baby will have three copies of that chromosome. When this occurs, the extra copy of the chromosome is present in every cell of the body.
How is trisomy diagnosed?
Genetic defects, such as trisomy 13 and trisomy 18, can be diagnosed before birth using prenatal non-invasive testing (NIPT). During this type of screening, an obstetrician, general practitioner, or genetic counselor draws a simple sample of blood and analyzes the DNA in placental cells circulating through it. These placental cells are identical to the cells of the growing child. NIPT can be performed in-office. The procedure is quick, effective, and presents no risk to the mother or baby.
What are the common types of trisomy?
The three most common types of trisomy are:
- Trisomy 21 (Down syndrome)
- Trisomy 18 (Edwards’ syndrome)
- Trisomy 13 (Patau syndrome)
Babies with autosomal trisomy have birth defects, including intellectual deficiencies and shortened life expectancies.
Who is at risk of developing trisomy?
Trisomy occurs spontaneously during conception. Clinical research suggests that the most important risk factor for trisomy is maternal age. Mothers who are in their late 30s and early 40s are more likely to have a baby with a trisomy condition.
What are the symptoms of trisomy?
The symptoms of trisomy vary from child to child, and depend on the type of trisomy and severity.
Symptoms of trisomy 13 include:
- Low birthweight
- Cleft lip or palate
- Small head
- Eyes that are close together
- Heart defects
- Kidney problems
Symptoms of trisomy 18 include:
- Failure to thrive
- A thin or frail appearance
- Weak cry
- Slow growth
- High blood pressure
What can I do if I find out my child has a trisomy?
A diagnosis of trisomy can be both frightening and heartbreaking. Many babies born with trisomy only live for a few days or weeks; those that do survive suffer from lifelong learning disabilities and physical handicaps.
Your general practitioner or OB/GYN can refer you to a genetic counselor who can explain your risks in depth. They can help you make a decision that best aligns with your unique health history and needs.