Genetic Screening Tests for Women 35 or Older

If you're 35 or older, you probably know that you have a higher risk for pregnancy problems. To help rule out any concerns, your doctor may offer you some additional prenatal tests. Whether you want have these tests is up to you.

Remember that most healthy women aged 35 and into their 40s have healthy pregnancies and healthy babies. But there are several ways genetic tests can be helpful in caring for a pregnancy:

  • You'll gain peace of mind about your baby's health.
  • You can learn about and prepare for your baby's special needs if a genetic problem is found.
  • You can use the information to help make decisions about how best to care for your pregnancy.

Not all tests are without risks, and sometimes tests can have false results. Talk with your doctor about the risks, benefits, and limitations of each test so you can make the best decision for you. Here's an overview of the tests you may be offered.

Ultrasound

Moms of all ages usually have one or more ultrasounds during their pregnancy. This safe test uses high-frequency sound waves to produce an image of your baby. An ultrasound may be used to:

  • Confirm that you are pregnant
  • Determine whether your baby's heart is beating
  • See if you are carrying more than one baby
  • Estimate your baby's due date and see how your baby is growing
  • Determine the baby's gender
  • Examine your ovaries and uterus
  • Determine the location of the placenta and the amount of amniotic fluid around your baby
  • Look for signs of birth defects such as cleft lip, heart defects, spina bifida, and Down syndrome

First Trimester Screen

This test is done between weeks 11 and 14. It involves a blood test and an ultrasound.

  • The blood test measures two markers in your blood.
  • The ultrasound measures the thickness of the back of your baby's neck.

Taken together, the results look for problems with your baby's chromosomes, such as Down syndrome.

This test serves the same function as the quad marker screen (below), but allows your doctor to see your baby. It also tends to cause fewer false alarms. Sometimes it's combined with a second blood test like the quad screen, to give a result that is more accurate than either of the individual tests.

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Quad Marker Screen

A quad marker screen is a blood test performed between the 15th and 20th weeks of pregnancy. It measures substances in the blood that may show:

  • Problems with a baby's brain and spinal cord, called neural tube defects. These include spina bifida and anencephaly. The quad marker screen can detect about 75% to 80% of neural tube defects.
  • Genetic disorders such as Down syndrome. The test can detect about 75% of Down syndrome cases in women under age 35 and more than 80% of Down syndrome cases in women age 35 and older.

It's important to know that the quad screen only indicates your level of risk for birth defects. If the test shows a risk greater than the average risk of a 35-year-old woman, then the test is considered to be positive. The test can't diagnose birth defects, so a positive result doesn't mean that your baby has a birth defect. In most cases, the baby is healthy despite an abnormal test result.

If the test is positive, your doctor may suggest having diagnostic tests, such as:

  • Amniocentesis to check your baby’s chromosomes
  • Ultrasound to look for signs of birth defects

Amniocentesis

Unlike blood testing, which only shows whether you are at risk, amniocentesis is used to make a diagnosis. During the test, your doctor will insert a needle through the abdomen wall, using ultrasound images to help guide the needle into the uterus. He or she will remove a small amount of amniotic fluid from the sac surrounding your baby. This sample is then used to check the baby's chromosomes and test for genetic diseases. In addition to the most common chromosome problems, including Down syndrome, trisomy 18, trisomy 13, and Turner syndrome, the sample can also be tested for:

Chorionic Villus Sampling (CVS)

CVS is an alternative to amniocentesis, and it can be performed earlier in the pregnancy. Like amniocentesis, CVS can diagnose some diseases. If you have certain risk factors, you may be offered CVS as a way to detect birth defects during early pregnancy.

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During this test, a small sample of cells, called chorionic villi, is taken from the placenta. Chorionic villi are tiny parts of the placenta that are formed from the fertilized egg, so they have the same genes as your baby. To get the cells, a doctor passes a needle through the vagina or the abdomen, depending on the location of the placenta. The cells are used to check your baby's chromosomes, just like amniocentesis.

CVS and amniocentesis usually involve genetic counseling, where you speak with a counselor about your risk for genetic disorders. You will also learn about the risks and benefits of the procedures.

Noninvasive Prenatal Diagnosis

This newer blood test, also called cell-free DNA testing, is used to show whether you are at risk for having a baby with chromosome problems. Because it's done by using a sample of your blood, it's less invasive than amniocentesis or CVS.

The test is done between 10 and 22 weeks of pregnancy. It finds DNA from your baby floating around in your blood. The result determines the chance that your baby could be born with Down syndrome, trisomy 18, or trisomy 13.

Noninvasive prenatal diagnosis can detect about 99% of Down syndrome and trisomy 18 cases, which is much better than other blood tests. The majority of trisomy 13 cases can also be detected with this test.

If the test shows an increased risk for chromosome problems, your doctor may recommend CVS or amniocentesis to confirm the diagnosis.

Because this is a new test, not all insurers cover it. Check with your insurance company to see whether the cost of the test will be covered.

WebMD Medical Reference Reviewed by Traci C. Johnson, MD on November 10, 2018

Sources

SOURCES:

National Coalition for Health Professional Education in Genetics and National Society of Genetic Counselors: "Non-Invasive Prenatal Testing (NIPT) Fact Sheet."

UCSF Medical Center: "FAQS: Cell-Free Fetal DNA Testing."

MedlinePlus: "Amniocentesis."

MedlinePlus: "Ultrasound."

MedlinePlus: "Chorionic Villus Sampling."

Cleveland Clinic: "Quad Marker Screen."

Kid's Health: "Prenatal Tests."

© 2018 WebMD, LLC. All rights reserved.

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