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Prenatal Genetic Testing 101

What is genetic testing in pregnancy?

Genetic testing during pregnancy can give you information about whether your baby has certain genetic disorders. Genetic disorders occur when there is missing or extra genetic information, mutations in the genetic information, or may be inherited. There are two types of prenatal genetic tests: screening tests and diagnostic tests. A screening test can tell you the chance that your baby has a genetic disorder. If your screening test is positive, a diagnostic test may be performed to determine if your baby actually has the disorder. Check out our video on the two most common types of Genetic Testing.

Carrier Testing

What is Carrier Testing?

Carrier testing is a type of genetic test that looks for recessive gene disorders in one or both parents.  We all potentially “carry” recessive genes for issues that we can pass on to our children, but (if you remember the patterns of genetic inheritance from high school biology class) recessive genes stay hidden unless both parents contribute the gene to their offspring.  This means that you and your partner or sperm donor would both have to carry the same recessive gene in order for there to be any chance of your child having this type of genetic disorder.  

Because this test evaluates your genes (or your partner’s), it really has nothing to do with your pregnancy, but since you are now growing your family, knowing your carrier status might feel important to you. Carrier testing is something that only needs to be done once in your life so if you have already had carrier testing, you do not need to repeat it. Often, our patients will choose to test one partner, wait for results to see if they are a carrier & then test the partner or sperm donor to see if there is any overlap in the partnership’s carrier status.

What kind of tests are available? 

Our genetic testing partner, Sema4, offers a variety of carrier testing panels for you to choose from.  

  1. You could opt to be tested for a small set of the most common recessive gene disorders (cystic fibrosis, spinal muscular atrophy, fragile X, tay sachs). 
  2. You could opt to be tested for a list of disorders targeted to a particular ethnicity or background that you might share (for example, people with Ashkenazi jewish or African American heritage have higher incidence of certain recessive gene disorders). 
  3. You could opt to do an “expanded panel” that would test you for hundreds of recessive gene disorders.  We like to warn our patients that when we test for this many things, it is very likely that you will come back as a carrier for something but because many of the disorders are very rare, it is very unlikely that you and your partner will have any overlap in your carrier status. 
  4. You could opt to skip this type of testing entirely! 

How is the test done?

This test is done as a blood test or, in some cases, a saliva sample. The results take about two weeks to come back.  If you come back as a “carrier” for one or more conditions, our next recommendation will be to test your partner or sperm donor via a blood or saliva test. Your partner’s test will also take about two weeks to result. If you and your reproductive partner both carry the same gene for the same disorder, we will refer you to speak to a genetic counselor about next steps.  If you don’t have any overlap in your carrier status, your children might also carry the recessive gene, but they will not be affected by the disorder. 

Will my insurance cover this?

Most insurance companies will cover this type of testing, though some of the “expanded panel” options are not fully covered. If you do end up having to pay out of pocket, the lab will revise the sticker price of the test to a maximum of $250 per person. 

Why would I choose this?

If you have any genetic conditions in your family or community, you might want to learn more. If you’re someone who “likes all the information”, this will definitely provide you with useful information about your genetic carrier status that you will have for the rest of your lifetime. Negative results can be reassuring. If partner results are available, they can be reassuring or helpful in gathering more information before making clinical decisions about your pregnancy care.

Why would I not choose this?

If your sperm or partner genetic testing is not available and therefor you are not able to get a full picture of the carrier risk to your pregnancy, that may cause unnecessary stress to your pregnancy. If you are someone who knows that you would not change the course of your pregnancy care, either diagnostic testing or termination of pregnancy, based on genetic information, then the results may not be useful as a screening tool.

NIPT

NIPT stands for Non-Invasive Prenatal Testing.  It refers to a prenatal screening blood test we offer to evaluate some of your baby’s chromosomes when you are at least 10 weeks pregnant.  NIPT has become the gold standard in prenatal chromosomal screening, and is likely to be covered by your insurance. 

How does this test work?

NIPT is done with blood drawn from the pregnant person. At the specialized genetics lab, they are able to tease out tiny fragments of fetal DNA that are floating in the pregnant person’s bloodstream. By evaluating this “fetal fraction” they are able to tell us if the baby has any issues with the chromosomes included in the test panel.

Which chromosomes are included? 

The most reliable of the NIPT testing options looks at chromosomes 13, 18, 21 & the fetal sex.  For these four core elements, this test is VERY good.  We have a greater than 99% confidence in the results. Because this is a screening test, there is still a small chance (less than 1%) of a false negative or false positive result, but for these four core elements that risk of an incorrect result is very low.

Are there other options to test for more things?

The lab offers additional “add on” options to look at more chromosomes (15, 16, 22), sex chromosome aneuploidy (too many or too few of the X or Y chromosomes) or “micro-deletions” (abnormalities in a portion of a chromosome).  The test reliability for these extra elements is not as good as for the four core elements.  This means that these added conditions have a higher chance of the test identifying a false negative or a false positive result. 

What if I don’t want to know the sex of my baby?
We never release the information about your baby’s sex without your permission.  Usually we will ask the testing company to report the sex to us (in case you change your mind and decide later in your pregnancy that you’d like to know, and so we can share the information with the team that does your ultrasounds), but we won’t share it with you unless you tell us you want to hear it. And, sure, we can share the sex of your baby to you in a sealed envelope in case you want to reveal that information in a special way.

What will happen if my NIPT comes back “high risk”?
In this case, we will send you for a consultation with a genetics counselor.  You might opt to have an “invasive” genetic test like an amniocentesis (amnio) or a chorionic villi sampling (CVS) as a follow-up. These procedures sample some genetic material from inside the pregnancy and can tell us with 100% certainty whether your baby has a chromosomal abnormality.

If the “invasive” test is 100% certain, why don’t I just have that test?

Tests like amniocentesis or a chorionic villi sampling can, in rare cases, result in pregnancy loss.  When we need these invasive tests, the risk is often worth the benefit, but we recommend that you do the non-invasive testing first. NIPT is an excellent test – it’s low risk & it’s reliable – and for most people it eliminates the need for the riskier diagnostic testing. 

Why would I choose this?

If you know that if you were carrying a fetus with a chromosomal abnormality you would not want to continue the pregnancy and would consider termination, this is the earliest test available to determine this  not ’re someone who “likes all the information”, this will definitely provide you with useful information about your genetic carrier status that you will have for the rest of your lifetime. Negative results can be reassuring. If partner results are available, they can be reassuring or helpful in gathering more information before making clinical decisions about your pregnancy care. If you want to know the sex of the baby as early as possible, this is the path toward that information.

Why would I not choose this?

If knowing your fetus carries a chromosomal abnormality would not impact your decision to carry your pregnancy to term (or terminate) or if you’re comfortable waiting for genetics screening and assessment of normal fetal development until later in the pregnancy through other screening tests. If you consider yourself low risk for chromosomal abnormalities based on your age and other risk factors, you may prefer to opt-out of optional screening tests.

Nuchal Translucency (NT) 

What is the NT test?

The Nuchal Translucency is a specialized ultrasound done between 11-13 weeks in your pregnancy. During the ultrasound the sonographer and Maternal Fetal Medicine doctor will take an overall look at your baby, measure the “crown-rump” length (top of the head to the bottom of the tailbone) to confirm that your due date is correct, and they will pay particularly close attention to an area at the back of the baby’s neck called the nuchal fold or nuchal translucency (NT).  

What do the results mean?

Abnormal measurements of the nuchal translucency (NT) can be soft markers for cardiac defects and chromosomal abnormalities and other syndromes, but the measurement is not 100% diagnostic.  If your baby has an abnormal NT measurement, our team will take a broader look at your prenatal testing to see if there are any other reasons for concern.  We will recommend that you see a genetic counselor to discuss the finding, and to make a plan for follow-up testing.  

Why would I choose this?

If you are opting to have a dating and viability ultrasound, this test is easily incorporated into that already standard of care visit at a partner testing unit. If you want all possible information about chromosomal and genetic abnormalities as soon as possible, this gives you additional information that may reassure you about the well being of your fetus’ development during the first trimester. 

Why would I not choose this?

If knowing your fetus carries a chromosomal abnormality would not impact your decision to carry your pregnancy to term (or terminate) or if you’re comfortable waiting for genetics screening and assessment of normal fetal development until later in the pregnancy through other screening tests. If you opted in for the NIPT test and feel reassured by that information and had an office ultrasound to confirm your dating, you may prefer to limit ultrasound exposure. If you consider yourself low risk for chromosomal abnormalities based on your age and other risk factors, you may prefer to opt-out of optional screening tests.

AFP

What is the AFP Test?

AFP is a protein made by the growing baby that can be found in a pregnant person’s blood or amniotic fluid. The MSAFP (Maternal Serum Alpha- FetoProtein) is collected through a blood draw at our office. The test is commonly covered by insurance as part of standard pregnancy screening. 

Why do we offer AFP screening?

AFP is a screening test to evaluate your baby for a type of birth defect called a neural tube defect. The neural tube is what forms the brain, spine and spinal cord of the baby. Neural tube defects happen when the neural tube does not close correctly and can lead to conditions like spina bifida. 

When can I get the AFP?

Your blood work can be drawn between 15 weeks and 22 weeks and 6 days. For your convenience, you may choose to have the blood drawn during your 16 week in-person visit at Oula. 

What do the results mean?

The AFP test is a screening test and the results will fall into “Low Risk” or “High Risk”. If your AFP blood work shows an elevated risk for neural tube defect, you will be referred for an ultrasound. 

Why would I do this?

This is the final bloodwork offering for genetic testing, if you are “all in” on genetic testing, this is the last piece of the puzzle in addition to your 16 week and 20 week anatomy ultrasounds. 

Why would I not do this?

If you feel reassured by earlier genetic testing that you opted in for, if you are comfortable with ultrasound screening as a tool for identifying abnormalities or if you prefer a “less is more” approach to your pregnancy testing journey, you may opt out of this test.