Published on March 13, 2023

Prenatal Genetic Counseling: Learning About Your Baby Before They're Born

man and woman cradling her pregnant belly

Genetic testing is a service that is offered in all pregnancies and provides you and your obstetric care provider with information about the health of your baby.

Genetic counselors, like those at EvergreenHealth, are able to help you understand the various tests you may consider during your pregnancy. This includes discussions about the health conditions we evaluate for and the accuracy of different testing options. They are also trained to help you decide what tests may or may not fit with your personal beliefs and pregnancy goals.

Understanding Genes

Typically, every cell in your body has 23 pairs of chromosomes. Each chromosome contains hundreds or thousands of genes, which are made up of DNA. These genes provide the information to tell your body how to grow and develop.

There are chromosome conditions and genetic conditions that can develop during your baby's development. A chromosome condition occurs when there is an extra or missing chromosome. A genetic condition occurs when a gene has been altered so it no longer functions as expected.

Which Conditions Can We Screen For?

There are many conditions that can be screened for during pregnancy. These include chromosome conditions, birth defects and genetic conditions.

Chromosome conditions include:

Down syndrome: This occurs when there is an extra copy of chromosome 21 in every cell. Children with Down syndrome commonly have developmental delays and have an increased chance for heart defects and other health conditions. For more information visit Understanding Down syndrome.
Trisomy 13 or Trisomy 18: This occurs when there is an extra copy of chromosome 13 or 18 in every cell. These are very rare chromosome conditions and most often result in a miscarriage. Children born with these conditions have a shortened life expectancy and typically require significant medical care.

Most often chromosome conditions happen by chance and do not run in families. For most pregnancies the chance of a chromosome condition is <1%.

Birth defects include:

Spina bifida/neural tube defects: Spina bifida occurs when the spinal column doesn't close completely and leaves and opening in the neural tube. Neural tube defects cause damage to the nerves of the spine. The condition can range from mild to severe depending on the location and number of nerves involved. More information is available from the Centers for Disease Prevention and Control.

With no family history, there is a 0.01% chance of a neural tube defect in pregnancy. Neural tube defects may run in families therefore the risk is higher if a family member has the condition.

Heart defects: Heart defects occur when the heart does not form correctly during early fetal development. There is a wide range of heart defects, from mild defects that do not require treatment to severe defects that require one or more surgeries to correct.

With no family history, there is a 0.5% chance of a heart defect in pregnancy. Heart defects may run in families therefore the risk is higher if a close family member has the condition.

Screenings and Genetic Testing

Depending on your preference, you can have screenings and genetic testing during your pregnancy for as many or as few of these conditions as you decide.

There are two categories of testing available in pregnancy, screening and diagnostic.

A screening test will estimate the chance of a condition in pregnancy. The results are typically high or low risk. A diagnostic test will tell for certain if a condition in present. These results give a yes or no answer.

Screening tests include:

Nuchal Translucency (NT) ultrasound: Between 11.5-13.5 weeks of pregnancy, ultrasound can measure the nuchal translucency, the fluid-filled area at the back of the baby's neck. If the measurement is normal the chance for chromosome conditions and heart defects is decreased. If the measurement is increased, the chances for chromosome conditions and heart defects are also increased. When there is an increased measurement then you will be offered genetic counseling and additional testing. This ultrasound detects about 70% of pregnancies with Down syndrome.
Combined screen/first-trimester screen: This screening combines the nuchal translucency ultrasound with a blood test to evaluate proteins and hormones that cross from the pregnancy into the pregnant person's bloodstream. It evaluates the chance for Down syndrome and trisomy 18 in pregnancy. It detects about 86% of pregnancies with Down syndrome and 75% of pregnancies with trisomy 18. The false positive rate is about 5%.
Non-invasive Prenatal Testing (NIPT): This screening is a blood test that evaluates cell-free DNA from the pregnancy that crosses into the pregnant person's bloodstream. Testing can be performed after nine weeks of pregnancy. It evaluates the chance for Down syndrome, trisomy 18 and trisomy 13. It may also evaluate for extra or missing copies of the sex chromosome and provide a fetal sex prediction. It detects about 99% of pregnancies with Down syndrome, 99% of pregnancies with trisomy 18 and 92% of pregnancies with trisomy 13. The false positive rate is less than 1%. The fetal sex prediction is 98-99% accurate.
Alpha-Fetoprotein (AFP) Screen: This screening is a blood test that evaluates alpha-fetoprotein (AFP) from the pregnancy that crosses into the pregnant person's bloodstream. Testing can be performed between 15 and 23 weeks of pregnancy. It evaluates the chance for neural tube defects including spina bifida. It detects about 80% of pregnancies with a neural tube defect. The false positive rate is about 2%.

Individuals who receive a "positive" or "high risk" result on a screening test will typically be referred for genetic counseling to discuss their results in more detail and make a plan for follow-up, which may include diagnostic testing, ultrasounds or a referral to a specialist.

Diagnostic tests:

Diagnostic testing follows screening tests. These tests are typically more invasive and offered following a screening tests that show your baby has a higher risk of a chromosome or genetic condition. Diagnostic tests have no false negatives or false positives.

Chorionic Villus Sampling (CVS): This test takes a small sample of the placenta. Testing is typically performed between 10-14 weeks of pregnancy. CVS can diagnose or rule out chromosome conditions including Down syndrome. If there is a known chance for other specific genetic conditions these can be diagnosed or ruled out as well. CVS is invasive and therefore is associated with a small risk of miscarriage, less than 1%. The Washington State Department of Health provides an informational video on CVS that explains the procedure in more detail.
Amniocentesis (amnio): This test takes a small sample of the amniotic fluid around the baby. Testing is typically performed between 16-20 weeks of pregnancy. Amnio can diagnose or rule out chromosome conditions including Down syndrome. If there is a known chance for other specific genetic conditions these can be diagnosed or ruled out as well. Amnio is invasive and therefore is associated with a small risk of miscarriage, less than 1%. The Washington State Department of Health provides an informational video on amnio that explains the test in more detail.

Making a Decision About Testing

You may choose to have prenatal testing for many reasons. You may want testing to learn more about the health of your baby. You may simply want the reassurance that all is well. You also may feel that the results will help you make informed decisions about pregnancy management, help you prepare for delivery, or help in making decisions for your baby's care after birth.

You also may choose to decline testing for many reasons. You may want to avoid the potential stress you might feel if you were to get a positive or high-risk result from the screening tests or you may not think the test will help you plan or make decisions.

Only you can decide if prenatal testing is right for you based on your beliefs and personality. As your healthcare partner, genetic counselors are here to provide you with information to support your decisions about genetic testing during pregnancy.