by: Janine M. Mash, LCGC.

I remember when I was pregnant with my first child, I had this moment thinking “I can’t wait for this baby to be born so I can stop worrying about her.”  It was then that I realized this underlying worry I’ve been carrying around was never going to go away. I’ll be a parent, and I’ll always worry about my daughter.  While this was true, it was certainly a relief when the prenatal genetic screening came back negative. Most likely, my baby was not going to be affected with Down syndrome or the other common genetic conditions tested for.  My choice to perform testing was mainly a way to manage my anxiety. I wanted to know if my child might have these conditions so I could come to terms with the diagnosis before my baby was born.

The choice a pregnant mother makes regarding prenatal genetic testing is as varied as a birth plan.  Some people want as complete of a test as possible, opting to perform diagnostic testing, while others choose to decline all of it outright.  Many people end up somewhere in the middle, often choosing to perform the non-invasive screening tests first and take it from there. There are so many different kinds of genetic testing and ways to do it that it can be tricky to figure out what testing is right for you.

The purpose of prenatal genetic testing is to see if a baby could be affected with certain genetic conditions, such as Down syndrome.  Generally, there is no family history, so it can be helpful to test while pregnant. Partly to feel reassured if the testing is normal, and partly to determine next steps if its not.   

The condition most often looked for is Down syndrome, the most common genetic disorder. But many tests also look for trisomy 18, trisomy 13, and other chromosome problems.  They can also assess recessive conditions such as cystic fibrosis, spinal muscular atrophy, sickle cell anemia and thalassemia.

All prenatal genetic testing is optional; it’s your choice to have these tests performed or not.  At the same time, all prenatal genetic testing is also an option. It is available to every pregnant woman regardless of age or risk. There are no right answers. A person will choose what type of tests, if any, they would like to perform based on their own individual ideals, values and ethics.

What tests are available?

There are two main forms of prenatal genetic testing: screening tests and diagnostic tests.  

Types of prenatal screening  includes:

  • Carrier screening
  • Maternal serum screening
  • Ultrasounds
  • Cell-free fetal DNA testing (ex: Panorama or Harmony)

Screening tests aim to provide a risk number of how likely a pregnancy is affected a condition.  This does not tell us if a baby has the condition itself, just how likely it may or may not happen (So a positive results doesn’t mean your baby has it, just that there is a higher risk). Screening is often used because its not invasive and doesn’t put the baby at risk. All screening tests have merit, but some are better at detecting the conditions than others, and have lower false positives.  That said, even the most accurate tests cannot tell for certain if a baby is affected due to the fact most screening tests rely heavily on statistics for their analysis.

Diagnostic tests, on the other hand, can tell for certain if a baby is affected with certain conditions.  However, they are invasive and require either a placental biopsy (CVS) or extracting fluid from around the baby (amniocentesis). Prenatal diagnostic testing carries a risk of miscarriage of about 1 in 300. Some people choose to perform diagnostic tests over screening since the results tell us for certain if the baby is, or is not, affected with Down syndrome or other chromosomal conditions.  However, most commonly, people will turn to diagnostic testing if a screening test showed the baby was at high risk.

There are no prenatal tests that can detect all genetic disorders. It’s estimated in each pregnancy, there is a 3-6% chance a baby might have a genetic condition or a birth defect. Prenatal genetic tests aim to assess the most common genetic conditions.

Why would I test?

There are many reasons why people choose to perform prenatal genetic testing. The most obvious reason is a person might choose to end a pregnancy if affected. However, even if the results would not change anything, there is still a lot of value in testing. A negative result is reassuring and can relieve anxiety.

If positive, knowing your baby may be affected with a genetic condition while pregnant, can help give time to come to terms with a diagnosis, meet other families, and get to know doctors and care providers that will be vital in a child’s care. Also, this knowledge might guide you into the place you feel most safe to have your baby.

I’m over 35, do I have to test?

Medicine tends make a fuss over women who are pregnant age 35 or older, because their individual risk to have a child affected with a chromosome problem is higher than if they had become pregnant in their 20s. That said, all pregnant women, regardless of age, are at risk to have a child affected with these conditions. This is why is your choice to perform testing or not.  Some people may be concerned and would like the information, while others don’t. Age may be a factor in your considerations, but it certainly is not required to perform prenatal genetic testing just because you’re over the age of 34.

I have no Family History… am I still at risk?

It’s counter intuitive, but most genetic disorders happen with out any family history.  Down syndrome most frequently occurs randomly, when an egg or sperm cell is created with too many copies of chromosome 21 . Cystic fibrosis, sickle cell anemia, and thalassemia are common autosomal recessive disorders. Parents are carriers of the condition, but are not affected themselves.  Carriers can run in families undetected for generations. If you do have a family history, then your risk to have an affected child is higher than someone who does not, but every person who is pregnant does carry some risk as well.

What’s right for me?

It is recommended every pregnant woman be offered prenatal testing during a pregnancy regardless of age or family history.  

This recommendation is more strongly suggested if you are:  

  • 35 years of age or older
  • Have a family history of certain genetic conditions
  • Have had more than 3 miscarriages
  • Feeling anxiety over the possibility a child could be affected.

Genetic counseling can help you determine what types of tests you want.  In genetic counseling we’ll cover your specific risk to have a child affected with Down Syndrome and other conditions based on your age and family history.  Then we will discuss the types of tests available and create a plan that is right for you, even if that means no testing at all.

Genetic counseling is now available at the SF Birth Center through San Francisco Genetic Counseling.

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