Down Syndrome Risk by Age

Trisomy 21 is more commonly known as Down syndrome. This is the most common condition of the chromosomes in the United States. There are roughly 1 in 700 infants born with the condition. Everyone has 23 pairs of chromosomes in every cell of their bodies. Every pair has a chromosome from the father and one from the mother. With Down syndrome, there is an extra copy of chromosome 21. This changes how the brain and body develop. There is correlation to Down syndrome risk by maternal age.

Risk of Baby Born with Down Syndrome by Maternal Age

We don’t know all the reasons Down syndrome can happen. It can be that either the sperm or egg coming together during fertilization has an extra chromosome. Down syndrome risk by age will go up.

Maternal Age

Number of Down Syndrome Fetuses at 16 weeks

Number of Down Syndrome Babies Born

15-19

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1/1250

20-24

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1/1400

25-29

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1/1100

30-31

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1/900

32

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1/750

33

1/420

1/625

34

1/325

1/500

35

1/250

1/350

36

1/200

1/275

37

1/150

1/225

38

1/120

1/175

39

1/100

1/140

40

1/75

1/100

41

1/60

1/85

42

1/45

1/65

43

1/35

1/50

44

1/30

1/40

45 and older

1/20

1/25

These numbers are rounded and approximate. With the data, geneticists have made the low-risk and high-risk separation at 1/250. There is a difference in numbers of 16-week-old fetuses and babies born alive, because of the spontaneous miscarriages that occur during this time.

After the age of 40, you should speak with your doctor about your specific risk. A genetic counselor is trained to help you understand genes and birth defects as well as other conditions that can run in families. If you have already had a child with Down syndrome, your risk will go up with each pregnancy. Translocation Down syndrome can be passed from parent to child but it is considered rare.

Screening Tests for Down Syndrome in Pregnancy

Down syndrome risk by age may increase, but screening is offered to everyone as routine. These screening tests can determine the likelihood that a mother has a baby with Down syndrome. These tests include:

Combined Test in First Trimester

  • Blood Test: This measures the amount of pregnancy-associated plasma protein-A or PAPP-A as well as the amount of HCG or the human chorionic gonadotropin. If there are abnormal levels of either, there may be a problem.
  • Ultrasound: They will also use the ultrasound to check an area at the back of your baby’s neck. This is the nuchal translucency screening test. If there are problems, there may be fluid there. With your age, ultrasound and the blood work, your doctor will estimate your risk.

Integrated Screening Test

This test is done in two parts, spanning both the first and the second trimester. The results are put together to estimate your risk of a baby with Down syndrome. This test has a lower rate of false-positives.

  • First Trimester: A blood test for measuring PAPP-A and an ultrasound for nuchal translucency are used.
  • Second Trimester: This uses a quad screen to measure four different levels in your blood: HCG, estriol, alpha fetoprotein and inhibin A.

Fetal Cell-Free DNA Analysis

This test checks for DNA found in the mother’s bloodstream. It is recommended for those with higher risk of having a baby with Down syndrome or as a follow up from a positive with other tests. This is a more specific test and if it indicates a high risk of Down syndrome, more invasive diagnostics may be used to see if the baby truly has Down syndrome.

Diagnostic Tests for Down Syndrome in Pregnancy

You already know the Down syndrome risk by age. If you discover a positive during your screening tests, you are at greater risk for having a baby with Down syndrome. Now you can consider confirming with diagnostic testing.

Amniocentesis

A sample of the amniotic fluid around the baby will be taken. With this sample, a determination about the chromosomes can be made. This is usually done around 15 weeks or during the second trimester. There is a slight risk of miscarriage, which is higher if done before 15 weeks.

Chorionic Villus Sampling (CVS)

With this testing, placental cells are taken to analyze chromosomes. This is usually done in the first trimester but after 10 weeks. This has a slightly higher risk of miscarriage than amniocentesis.

Cordocentesis

With this test, a sampling is taken from the umbilical blood and examined for chromosomal defects. This can be performed between 18-22 weeks of pregnancy. It has a higher risk for miscarriage than amniocentesis and CVS. For this reason, it is only offered when results from other testing warrant it.

For those utilizing IVF, preimplantation genetic diagnosis can be used to test the embryo before it is implanted in the womb.

What Can You Do During Pregnancy?

Regardless of Down syndrome risk by age, you should remember it occurs before you conceive. Nothing you can do to change this for better or worse during pregnancy. All you can do is care for you and your unborn baby by eating well, following your doctor’s advice and taking your vitamins. If you receive a diagnosis of Down syndrome, the ndss.org or National Down Syndrome Society can offer you guidance.

Diagnosis of Down Syndrome in Newborns

When the baby is born, Down syndrome is generally diagnosed on appearance. Some common symptoms are a flat back of the head, a small mouth with a protruding tongue, reduced muscle tone, broad hands with short fingers, etc.

Your doctor will also likely ask for a chromosomal karyotype test as well. This tests a blood sample for extra chromosomes.

 
 
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