During the first trimester, women are offered many options for medical and genetic testing. All moms-to-be should have their blood drawn and urine tested, but pregnant women with increased risk factors for genetic conditions (including a family history of chromosomal disorder or being 35 years of age or older on your due date) may be advised to undergo further tests. Typical medical tests ordered during the first trimester include the following, although not all women will need or choose all of these options.
Blood tests
At the very first prenatal appointment, a healthcare provider will usually have draw blood and test it for a number of factors, including blood type, red blood cell count, Hepatitis B, HIV, Rh-factor, syphylis and rubella. The healthcare provider will do this to make sure there is no disease or deficiency that could affect a pregnancy. In the case of the Rh-factor, they will make sure that the immune system does not identify the fetus’ blood cells as foreign bodies, as it does for viruses and bacteria. Just about all women will have their blood tested at the first prenatal visit.
Urine tests
Urine tests are going to be a staple of each prenatal appointment. The healthcare provider will check urine for the elevated presence of either protein or sugar, both of which can indicate serious pregnancy-related conditions like preeclampsia or gestational diabetes.
Chorionic villus sampling
Chorionic villus sampling (CVS) is an invasive diagnostic procedure that can obtain cells to help detect chromosomal defects in pregnancy. Women who have a family history of chromosomal disorders or are over 35 years of age on their due date are typically offered CVS, but most do not need it unless their first trimester screen showed any risk. The chorionic villus sampling includes taking placental cells (containing the same genetic material as baby’s cells) and testing the cells for chromosomal disorders, and is most commonly performed between weeks 10 and 13 of pregnancy.
First trimester combined screen
Performed between weeks 11 and 14 of pregnancy, the First Trimester Combined Screen is a testing option that consists of a maternal serum screening mest (MSS) and a Nuchal Translucency (NT) ultrasound examination. The MSS tests for pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG) – abnormal levels of both can indicate a chromosomal disorder. In addition, the NT ultrasound is performed to determine the size of clear space (fluid) in the back of the unborn baby’s neck, which can also indicate a risk of Trisomy 21 (Down syndrome), or other developmental conditions. The First Trimester Combined Screen is not diagnostic, it merely screens for an increased likelihood of having certain chromosomal disorders. Although it identifies ~85% of unborn babies with Down syndrome, 5% of those tested will also register a false positive result. Because Down syndrome is relatively rare, the majority of pregnant women who get a positive Combined Screen test result will deliver a healthy baby. The First Trimester Combined Screen is highly effective at screening for chromosomal disorders – it provides the odds of an unborn baby having a disorder (e.g., 1/1000) rather than conclusive results for the genetic disorders.
Cell-free fetal DNA testing
This test is indicated as early as week 10 of pregnancy and is a highly accurate way of assessing for chromosomal fetal abnormalities (abnormal number of chromosomes). Because some of a fetus’ DNA crosses the placenta and makes its way into the mom’s blood stream, this DNA along with placental DNA can be analyzed to determine if a fetus might have any chromosomal abnormalities. These tests are a great way to look for the possibility of a chromosomal disorder without the risk of miscarriage. Cell-free fetal DNA testing is appropriate for any woman who is at increased risk for having a pregnancy with a chromosomal abnormality, including advanced maternal age, an abnormal serum screening test, a fetal ultrasound finding suggestive of chromosomal abnormalities, or a personal or family history of chromosomal abnormalities.
Sources
- Amy Swanson, Amy J. Sehnert, Sucheta Bhatt. “Non-invasive Prenatal Testing: Technologies, Clinical Assays and Implementation Strategies for Women’s Healthcare Practitioners.” Curr Genet Med Rep. 1(2): 113-121. Web. 6/13/2015.
- Mayo Clinic Staff. “Prenatal care: 1st trimester visits.” Mayo Clinic. Mayo Clinic, 7/31/2015. Web.
- “Prenatal care in your first trimester.” U.S National Library of Medicine. MedlinePlus, 6/11/2014. Web.
- “Prenatal tests.” March of Dimes. March of Dimes, 6/3/2016. Web.
- Mayo Clinic Staff. “Chorionic Villus Sampling.” Mayo Clinic. Mayo Clinic, 10/17/2015. Web.
- Mayo Clinic Staff. “Noninvasive prenatal testing.” Mayo Clinic. Mayo Clinic, 2/23/2013. Web.
