Pregnancy can be a time fraught with many questions and fears:
What can I eat? What should I eat?
What medications are safe?
How much weight should I gain?
— And the one that seems to loom largest and produce the most anxiety in the patients I see:
How do I know my baby’s OK?
Well, you don’t……at least not 100%. But there is definitely information to be had. There are many different tests available designed to give you information about your growing human and its DNA.
The best case scenario is when a patient actually comes to see me for a Pre- conception counseling session. That is the best time to take a look at your age, family history and medical history and decide what types of risks you may be undertaking by getting pregnant, and how likely you may be to pass some of your own risks onto your baby.
At that visit, unburdened by an already-forming human, and an already determined combination of DNA, there is TIME. Time to identify whether the illnesses that exist in your family (or in the father of the baby’s family) can potentially be passed down to another generation. Time to find out if the area of the world that your ancestors came from has special or specific conditions or illnesses that would make it more likely they’d show up somewhere down the hereditary line. (think sickle cell anemia, or other anemias that are particular to certain areas of the world). This is the time to assess, based on your age and medical conditions if pregnancy is even safe, or recommended. (I am continually amazed at how many women I see who seem to have no idea that their Type 1 Diabetes or high blood pressure may be reasons not to get pregnant at all) We can sit down at this pre-conception visit and discuss all potential risks, as well as how to lower those risks and have a healthy pregnancy.
But let’s be realistic — only about 5% of patients come to see me before they get pregnant. Almost everyone comes in only after they get the positive pregnancy test. By the second prenatal visit, we need to have a detailed conversation about information — just what information do you want to know about the health and the genetics of your growing baby? And how certain — how precise do you want that information to be?
First let’s talk about the different types of tests available:
1- CARRIER SCREENING:
This is a test that looks at whether or not you carry, within your DNA, various traits for conditions that can be passed down to your baby. Ideally, these types of screening tests would be done before pregnancy, but they may also be done during pregnancy, usually in the first trimester. This test will check for Cystic Fibrosis, and Fragile X syndrome, (two conditions with major health implications) but there are panels of tests that can check for over a hundred different conditions. If it turns out that you are a carrier for one or more of these conditions, then the father of the baby should be tested as well, since these are conditions that cannot be passed down to a baby unless both carry the same abnormal gene.
2- DIAGNOSTIC TESTING:
Diagnostic testing of your baby’s DNA is 100% accurate (with some rare exceptions) in telling you whether your baby has a normal number of chromosomes. They cannot test those chromosomes for every single disease that exists, but a diagnostic test will tell you if your baby has Down Syndrome, or other conditions where there are too many or too few chromosomes (all of which would lead to various levels of compromise in your baby). Why don’t more people opt, then, for diagnostic tests? Because diagnostic tests are also called “invasive tests”; in order to get a sample of your baby’s DNA and to tell you with 100% accuracy what your baby’s chromosomes look like, there needs to be a needle — -a pretty long needle. That needle either goes into the area where the fetus is implanted into the wall of the uterus via its attachment to the placenta (the chorion), or directly into the fluid-filled sac around the baby (the amniotic sac). The first one is called Chorionic Villus Sampling, or CVS, and is done between about 10 to 12 weeks of pregnancy. The second one is called an Amniocentesis, and is done between 16 to 18 weeks of pregnancy. Since these are “invasive” procedures, they do come with a small degree of risk, that the amniotic sac could rupture, or that there could be bleeding or a miscarriage. That’s why these tests are really only recommended when the probability that there actually IS a chromosomal abnormality is higher than the risk of the procedure itself. This means women who have already had a child with a chromosome abnormality, women who have family members with known chromosomal abnormalities, and women over the age of 35 should be offered these type of diagnostic tests, as they are all at higher risk to have a baby with a genetic problem.
Many patients in my practice have made their decisions regarding the remainder of their pregnancy based on results from diagnostic testing. Sometimes, that meant terminating their pregnancy. Sometimes, that meant preparing for a baby with special needs. And sometimes that meant choosing to deliver at a hospital with a high level nursery in order to care for a newborn with special medical needs. Often it meant a sigh of relief after weeks of worry, now being assured that their baby has a normal complement of chromosomes.
3- SCREENING TESTS:
ANY test that is NOT a diagnostic test is a screening test. Results from a screening test are never going to give 100% assurance in their result. A screening test is designed to look at a certain number of factors, put them all together, and give a “risk analysis”. For example, a prenatal screening test (and there are many) may look at a blood sample in the mother, check certain proteins or components of her blood, and then state, “looking at these components, the risk that the baby has Down Syndrome is 1 in 100,000”. How do they know this? By testing many many blood samples from many pregnant women, and looking at the outcomes of their pregnancies. IF the risk is “1 in 100,000”, that means that if they tested 100,000 women, and found exactly the same markers in their blood as they found in yours, then ONE of those babies is likely to have Down Syndrome. So — pretty good odds that the baby does NOT have it. Some screening tests look at blood tests and combine those results with a special ultrasound that is called a Nuchal Translucency test. This is an ultrasound in the first trimester which looks, specifically at the thickness of the neck of the developing fetus. There is actually a correlation between how thick the back of the neck is and the liklihood that the baby will have Down Syndrome. Combining the blood test with the ultrasound gives a more accurate risk analysis than just the blood test alone.
Many people do screening tests so they can feel reassured if they get a result that says their baby is very low risk to have a chromosomal abnormality. However, if the screening test says that there is a high risk that the baby has abnormal chromosomes, then the recommendation is always to follow up with a diagnostic test. No major decisions should be made based on a screening test alone.
One newer type of screening test is a Non Invasive Prenatal Test, or NIPT. This is a blood test on the mother where special tests are run to identify fetal cells in the mother’s circulation. If enough fetal cells are found, the DNA of these cells can be checked for abnormalities. Since this is also a screening test, the results are reported in the same way — as “the risk that the baby has Trisomy 18 is 1 in 100,000.” There can be false negatives (where the test says there is not problem, but there actually IS one), and false positives, (where the test says there IS a problem but there really isn’t one). No one should be making definitive decisions based on NIPT. If the NIPT flags a problem, then a diagnostic test is recommended before making any definitive decisions. This test can also tell the gender of the baby by noting if there is a Y chromosome is present (in which case the baby is a boy).
Of course, the majority of babies that reach nine months of gestation are born healthy and without abnormal DNA. Of course, there are patients who want to do no testing at all. In order to make a decision about what, if any testing to do, I always look at a patient’s age, medical and family history, as well as a patient’s desire for information, and make some recommendations. I also always ask this question:
“If you have the opportunity to have information about your baby’s chromosomes, and decide not to do any testing — -and then i deliver your baby and it turns out that baby DOES have a chromosomal abnormality, will you say to yourself, “I wish I had known about this sooner”, or will you say to yourself, “I am glad I didn’t know earlier” ?”
Only YOU know what the answer to that question would be…..there is a window for testing that can be done during pregnancy…Information can be powerful…..Act accordingly.