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What You Need to Know About Trisomies and Your Pregnancy

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Trisomies might be the most frightening of all birth defects, yet most parents have never heard of them. Today we’ll talk a little about trisomies, as well as three of the most common instances of this genetic defect.

What are trisomies?
Healthy humans have a total of 23 pairs of chromosomes. Trisomies occur when a fetus makes a copy, or partial copy, of one of these pairs of chromosomes. This leads to a genetic defect, which typically includes mild to severe mental retardation, as well as significant health problems and death.

Who is at risk?
The most common risk factors are advanced age (mother is 35 years or older) and/or a family history of genetic defects. That said, trisomies have been shown to appear in any pregnancy, even among young mothers without any familial history of genetic defects. However, age does play a key part in increasing the risk that your pregnancy will result in a genetic defect. We’ll talk in specifics about trisomies in just a moment, but first lets have a look at some numbers that show how much risk increases with age. These statistics are from a report by Queen Mary University of London that details risk of Trisomy 21 pregnancies across first world nations.
• 1 in 1350 at age 25
• 1 in 350 at age 35
• 1 in 35 at age 45

As you can see, instances of Trisomy 21 increase significantly with age, and the same holds true for other genetic defects (more on that in a moment) as well.

What are the most common trisomies?
The three most common trisomies are:
1. Trisomy 21 (Down syndrome)
2. Trisomy 18 (Edwards syndrome)
3. Trisomy 13 (Patau syndrome)

The first of the three, Trisomy 21, is the most common. Children born with trisomy 21 are born with a copy of their 21st pair of chromosomes, which leads to physical growth delays, characteristic facial features, and mild to moderate intellectual disability. Although they are at a high risk for a number of serious health conditions, such as congenital heart disease, many of these children go on to lead relatively normal lives (typically with assistance) and have a life expectancy around 50 to 60 years of age with proper health care.

Trisomy 18 and 13 are more rare, but typically result in a high infant mortality rate, with those that do survive birth typically dying within the first year of life (often within the first few days or weeks). The vast majority (98%) of these pregnancies are terminated.

What can I do to decrease risk?
Proper prenatal care, such as supplementing folic acid, abstaining from drugs, alcohol, or tobacco products, and keeping yourself generally healthy before and during your pregnancy have been shown to reduce instances of birth defects, including genetic defects. While this isn’t a cure-all, general health goes a long way in helping to ensure that you have a healthy baby. Outside of this, and getting pregnant earlier in life, there’s really not much you can do.

Is there a cure?
There’s no “cure” for children born with any of these genetic defects. However, there is the option for prenatal DNA testing, which won’t cure the condition, but will give you advanced knowledge that it exists. Typically, healthcare professionals will order these tests if you are of an advanced age, have a familial history of genetic defects, or positive serum screen or ultrasound finding. This noninvasive prenatal test is completed with just a small blood sample from the mother being sent to a lab by your healthcare professional. Results are typically available in your doctors office within 5 days of the date the lab received the sample.

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