Understanding Genetic Testing in Pregnancy
What it Can (and Can't) Tell You
The subject of genetic testing can feel, well… overwhelming. There are a ton of acronyms (as you’ll see below!) and stats, combined with a whole host of questions and what ifs. But think of it this way. Genetic testing is a way to understand more about your baby’s genetic make up.
How much you learn depends on the test you pick, and what you want to know.
I like to explain it like this. Your baby’s DNA (Deoxyribonucleic acid) is like a huge library. Each chromosome is a bookshelf, packed with books (your genes). And each book is filled with letters. These are the base pairs that make up DNA.
Genetic testing tells you more about that library. Some tests flip through the card catalog. Others look at pages in the books. Some read the text letter by letter.
If a chromosome is missing, or if there’s an extra one, a section of the library has disappeared. Or has been copied twice. And when there’s a missing piece or change in a gene? That’s like finding a typo in one book.
Some tests read the book titles. Others read every paragraph.
So, let’s get started with the most common genetic tests.
Carrier Screening: Looking at Your Library
Carrier screening is a simple blood or saliva test you can do before or during pregnancy. It checks for silent genetic changes you might carry without ever knowing it. Most carriers are completely healthy — they have no clue they’re carriers of anything. Carrier screening is important to get when both partners happen to carry a change in the same gene, because that can raise the chance of having a baby with a genetic condition.
Some people choose a basic panel that covers the most common conditions. Others go for the broader version that looks at hundreds of genes. The choice comes down to the level of detail you’re looking for.
Cell-Free DNA (cfDNA): Reading a Summary From the Library
The cell-free DNA test is also called NIPT or NIPS. This test looks at tiny fragments of your baby’s DNA that are circulating in your blood. Keep in mind this is a screening test, not an actual diagnosis. A cell-free DNA test can’t say for sure whether a baby has a condition. But it will tell you whether there’s a higher or lower chance.
cfDNA is excellent at finding major chromosomal changes.
Trisomy 21 (commonly known as Down syndrome)
Differences in the sex chromosomes, like Turner or Klinefelter syndrome
There are some cfDNA tests that look for smaller chromosomal deletions or duplications. That’s like specific missing or extra pages in the library we talked about earlier. These results can be less reliable.
If something unexpected shows up on a cfDNA test, your doctor will probably recommend a diagnostic test, like chronic villus sampling (CVS) or amniocentesis to confirm the results.
CVS and Amniocentesis: Opening the Books
Both chorionic villus sampling and amniocentesis (amnio) are diagnostic tests. They read the baby’s genetic library directly. Not just summaries like cfDNA.
CVS is done early on at about 11–14 weeks of pregnancy. It takes a detailed look at a tiny sample of the placenta.
Amniocentesis is usually done after 15 weeks and uses a small sample of amniotic fluid for the test.
There is a very small risk of miscarriage associated with these tests, but they provide the most detailed information available before birth.
There are various level of reading, depending on what you’re looking for.
Karyotype looks for big changes like missing or extra chromosomes (entire shelves) or pieces of chromosomes (books).
SNP microarray looks for smaller missing or extra pieces of DNA (pages or paragraphs).
Whole exome or genome sequencing reads the genetic text in minute detail, essentially looking for typos or changes in single letters (base pairs).
Amniocentesis or CVS might also be recommended if an ultrasound shows anything out of the ordinary. This helps your care team evaluate if there’s an underlying condition that might influence the test outcome.
Each level offers more detail, but that can also mean more uncertainty. Sometimes results show things we don’t fully understand. And as you can imagine, that can be very hard to navigate emotionally.
Why Are You Looking?
Before you decide on genetic testing, it’s a good idea to pause and ask yourself some questions. What exactly do I want to know? What would I do with that information?
Maybe for you, it’s about preparation. You might want to know early on if your baby will need extra medical care, or if the birth should happen at a specialized center. Or peace of mind — that reassurance that everything looks low-risk, might be at the top of your list. You might want to know all the possibilities, even when the next steps might not be clear.
There’s no single right reason to test. It’s also okay if your feelings change once you get the actual test results. Sometimes we learn something unexpected and need space and support, to process it.
Here’s the Bottom Line
Genetic testing looks at information about your baby before birth.
Think of your provider or genetic counselor as your guide through the genetic library. They’re there to help you decide which tests to take, which tests are most relevant for you, and when it’s okay to close the book.
There’s something new every day in the eDoula app. Daily practices, guidance, and support for your entire birth journey. Pregnancy, labor, delivery, postpartum, and beyond.