Is genetic screening recommended during pregnancy if you’ve had IVF?
February 20, 2024
When you conceive through in vitro fertilization (IVF), you may be offered preimplantation genetic testing (PGT) to examine the embryos before transferring them to the uterus. For some patients, PGT can optimize your success with IVF. For example, chromosome abnormalities in the early embryo are one of the most common reasons that an embryo may not continue developing to a healthy pregnancy.
In those with an increased chance for chromosome abnormalities, PGT can help identify embryos that are more likely to result in a progressing pregnancy, or for those with increased odds of a genetic disorder, a child unaffected by the known condition.
So, when we offer genetic screening or testing options again during the pregnancy, it’s not unusual for a patient ask: “Didn’t we already do that?”
And here’s the answer: PGT isn’t designed to catch every genetic variation. It screens for chromosomal differences that could result in miscarriage or specific conditions, such as Down syndrome, Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), Klinefelter syndrome and Turner syndrome, among others. PGT is not a guarantee that the pregnancy will be successful or that the baby won’t have a genetic condition.
Once you become pregnant, it’s like starting over with a blank slate in terms of your screening options. Any prenatal genetic screening and testing we offer patients who conceive naturally also makes sense to do after IVF.
What does PGT screen for?
There are three types of preimplantation genetic testing, or PGT:
- PGT-A is the most common type and analyzes the embryo for aneuploidy, in which there is an extra or missing chromosome. Examples of this are Down syndrome or Turner syndrome.
- PGT-M screens for monogenic disease, which is caused by the inheritance of a single gene mutation that one or both parents carries. Examples are cystic fibrosis and sickle cell disease.
- PGT-SR stands for structural rearrangements of chromosomes. This type of PGT is used when one of the parents carries a chromosome rearrangement that could potentially result in missing, extra, or rearranged chromosomes in an embryo. These problems can cause repeated miscarriages.
Any patient undergoing IVF can get preimplantation genetic testing, but it’s typically offered for those who:
- Are older than 35, due to increased risk of chromosomal anomalies in pregnancy.
- Are known carriers of a single gene disorder.
- Are known carriers for a chromosome rearrangement, such as a chromosome translocation.
How does PGT work?
When PGT is going to be performed, first embryos are created in the lab. The embryo is nurtured for a few days while cells grow and divide, until the embryo has about 100-200 cells. Then, a biopsy removes a few sample cells from the trophectoderm, or pre-placenta. Cells that will become the baby will not be disturbed. The sample will be sent to a laboratory to conduct genetic testing. Depending on the results, the embryo may then be transferred to the woman’s uterus.
PGT is not infallible. The cells that are biopsied and analyzed are usually representative of the full embryo, but some abnormal cells may still exist elsewhere in the embryo. And each type of PGT is specifically testing for a certain type of condition or even a single genetic condition.
The potential for false-positive and false-negative results in preimplantation genetic testing has prompted the American College of Obstetricians and Gynecologists (ACOG) to recommend that pregnant women who have had pre-implantation testing still be offered prenatal genetic screening, even if their PGT results are normal.
Options for genetic screening tests in pregnancy
Two types of genetic screening tests are available during pregnancy. One is carrier screening, which you may have already completed before beginning the IVF process. Carrier screening examines the parents’ DNA for potentially hereditary recessive or X-linked gene variants that could be passed to their baby.
The other type that is available for every pregnant person is to screen for chromosome abnormalities, most of which occur sporadically. If you have already undergone IVF and PGT-A, screening for chromosome abnormalities during pregnancy would be a confirmation test of the PGT-A results. A screening test that is available for every pregnant person is:
- Noninvasive prenatal testing (NIPT): Also known as cell-free fetal DNA (cffDNA) screening, it analyzes small fragments of placental DNA that circulate in a pregnant person’s blood. NIPT screen for the most common chromosome abnormalities, including Down syndrome, Edwards syndrome, Patau syndrome, or sex chromosome disorders such as Turner syndrome. There is also now an NIPT option to screen for some recessive conditions such as sickle cell disease in the fetus.
Diagnostic tests for chromosome abnormalities are also available to every pregnant person. Diagnostic tests provide a definitive answer about the chromosome status of a pregnancy or if the fetus is a carrier or is affected by a single gene disorder if there is known risk. However, they involve more invasive procedures and are associated with a very small risk for pregnancy complications or miscarriage. The two diagnostic testing options are:
- Chorionic villus sampling (CVS): CVS involves collecting a tissue sample from the junction of the uterus and first trimester placenta, which is then sent to a laboratory to test for genetic or chromosomal abnormalities.
- Amniocentesis: This test collects a sample of fluid from around the fetus to test for genetic or chromosomal or genetic abnormalities (including some that cannot be tested via CVS sample), infections, or indicators of spina bifida.
These tests may also be able to shed light on potential issues that show up in a fetal anatomy ultrasound, such as a fetal heart defect.
All genetic screening or diagnostic tests, including PGT, are optional. Plenty of people elect not to have genetic screening or test before or during pregnancy, and that’s OK. We discuss them with you so you are informed of your options and can make the best decision for you and your family.
To visit with a genetic counselor or maternal-fetal medicine doctor, call 214-645-8300 or request an appointment online.
More stories about pregnancy and genetics
UT Southwestern’s preconception and prenatal genetics service connects patients with board-certified genetic counselors specializing in genetic testing and pregnancy. Our team helps patients understand information and make decisions about genetic testing that are right for their family. Learn more.
