Genetic Testing In Pregnancy

Some new parents love mystery. Others are eager for answers! It's natural to want to know everything about your pregnancy as soon as possible. That's why almost 70% of mothers want to know the sex of their child before birth. That excitement for information is also why genetic testing in pregnancy has become both popular and widely recommended.

Modern genetic tests are designed to detect possible issues that may arise in a developing baby and to provide parents with information, options, and reassurance. Despite how modern or futuristic it may sound, genetic testing has been around in some form since the 1990s. Over the years, these tests have become more reliable and more common.

What is Genetic Testing?

You've probably heard of DNA being referred to as the blueprint for your body. That's mostly right. Your DNA is unique to you, and it's responsible for telling your body what proteins go where. Certain strands of DNA are tasked with determining the color of your eyes. Other sections of DNA control the color of your hair and so on.

Over the years, scientists and researchers have identified specific genetic codes responsible for certain medical complications and differences. Genetic testing is a process by which some genetic material is extracted and examined for DNA markers that may indicate possible irregularities.

What Types of Genetic Testing Can I Get?

Because they are designed to put as much information into the hands of parents as possible, there are numerous types of genetic testing in pregnancy available. Some of the most requested and most powerful tests include:

• Genetic Carrier Screening: This is a genetic test you and your partner can take even before becoming pregnant. A doctor will take a sample of blood and saliva and run your DNA through a screening process. These tests check for various issues you may be likely to pass on genetically to your children, such as Cystic Fibrosis or Tay Sachs Disease. Knowing how likely you are to pass on certain conditions can help you make informed family expansion plans.
• First Trimester Screen and Ultrasound: Around the 12th week of pregnancy, your OBGYN may offer what's known as a first trimester screen. This test combines a two-factor genetic screen with an ultrasound examination. The ultrasound portion is called a nuchal translucency screening and surveys the thickness of the back of the neck. The blood test portion of the screening looks for hormonal markers commonly associated with a higher risk of Down Syndrome, trisomy 18, and spin or neck problems.
• Maternal Serum AFP: Once mothers approach 15-18 weeks of pregnancy, they have the option of undergoing a simple blood screening called a maternal serum AFP. This test screens for a natural compound produced by all unborn babies called alpha feto-protein (or AFP). AFP is detectable in the mother's bloodstream, so a simple blood draw is all that is required. Especially high levels of AFP may indicate the presence or risk of certain birth defects, such as spina bifida. Normal or low AFP levels can indicate a healthy, developing baby and offer expecting parents welcome reassurance.
• Cell-free Fetal DNA Testing: Once you become pregnant, your infant's DNA can be found throughout your body. After ten weeks or so, there's enough genetic material floating around for a maternal blood sample to provide some general information. This test requires nothing more than a blood sample from the parent, but it provides some early checks for Down's syndrome, abnormalities with sex chromosomes, Trisomy 18, and Trisomy 13.
• Chorionic Villus Sampling: One of the oldest genetic screening tests, chorionic villus sampling, or CVS, is considered a diagnostic test (as opposed to a test that screens for elevated risk) and works by examining a small section of the placenta. This placental sample can be acquired either via an ultrasound-guided needle inserted through the pregnant person's abdomen into the uterus or a small tube inserted through the cervix. Typically, this test is performed somewhere between the 10th and 13th week of pregnancy. CVS can test for Down Syndrome, Trisomy 13, and Trisomy 18.
• Amniocentesis: Amniocentesis is also considered a diagnostic test (as opposed to a test that screens for elevated risk) for Down Syndrome, Trisomy 13, and Trisomy 18. Amniocentesis has the added benefit of screening for spinal defects or problems with brain development. This particular test works by inserting a long needle in through the tummy to take a sample of amniotic fluid.

Not every woman will undergo every genetic test. Less invasive tests, such as blood samples, are routinely offered parts of prenatal care. More invasive tests, such as amniocentesis and CVS can each cause cramping or bleeding and carry a slight risk of miscarriage, so they tend to be reserved for situational needs.

If I'm Pregnant, Should I Get Tested?

Because it can be performed before you ever become pregnant, genetic carrier screening is relatively popular and routine. But not every test is required for every pregnancy, and your OB GYN will generally not advise you to undergo unnecessary tests. In most cases, your OB GYN will recommend further genetic testing only should one of the following cases arise:

• A standard screening noted a possible issue: If one of the standard non-invasive prenatal genetic screenings (usually done via routine blood draws) noted a positive indication of an issue, your OBGYN may order a more detailed test in order to confirm the results.
• Genetic markers are present in your DNA: As a parent, if you have genetic markers that indicate you might be at higher than normal risk for certain abnormalities or issues, a more substantive test might be recommended.
• You are over 34: Current guidelines usually recommend that any pregnancies to couples over the age of 34 undergo genetic testing for possible issues.
• Other warning factors: If someone in your family has genetic markers for certain issues or genetic defects, your OB GYN may recommend testing. Likewise, if you have given birth to a child with a genetic abnormality in the past, there may be sufficient reason to order more comprehensive genetic tests.

What Will Genetic Testing Really Tell Me?

In every case, it is up to you as the parent to decide whether or not to undergo any genetic testing in pregnancy. Generally speaking, genetic testing is often very reliable. Even still, many tests are coupled with ultrasound examinations in order to confirm any findings, as both false-positives and false-negatives are possible.

Accurate as they are, genetic testing usually deals in risks and probabilities. The less invasive, less accurate tests will give you an indication of possible risks. The more accurate tests will provide some, but not absolute, certainty.

Generally, genetic testing will screen for issues such as:

• Chromosomal abnormalities
• Down Syndrome
• Neural tube defects
• Genetic diseases, such as Huntington?s Disease or Cystic Fibrosis

Risks and Concerns with Genetic Testing

There are benefits and possible drawbacks to any genetic testing. In cases of more invasive tests, the most common risks are bruising, bleeding and infection. Very rarely, miscarriage can result–it's a remote risk, but one worth discussing with your OB GYN.

For most parents, the concerns around genetic testing are ethical in nature. The question quickly becomes: what do you do with the information you have? Most families undergo testing for peace of mind–tests that come back clear and normal can give you comfort and help you focus on the joys of parenthood.

For other families, advance notice of possible issues can give them time to prepare. Some medical interventions may be able to lower the risks of genetic issues becoming severe at birth. That time to plan can be essential, especially if your infant might require extra care or accomodations.

Genetic testing and screening is a powerful tool. It's designed to give parents extra information so they can more accurately and more successfully plan for a new addition to their family. We offer a full range of obstetrics services at our offices in Wilmette and Glenview. If you have questions about genetic testing–what your options are and what your choices might be–you can schedule a consultation with a member of our staff and get personalized options and advice.