Common Tests During Pregnancy
There are several common screening tests that you will undergo during your pregnancy! Some are done every time you get your blood drawn, others you can choose to discuss with your doctor.
First Trimester prenatal screening tests is a combination of fetal ultrasound and maternal blood screening. This screening process can help evaluate risk of the fetus having certain birth defects.
- Ultrasound test for fetal nuchal translucency (NT) – is a completely non-invasive test that uses an ultrasound test to determine the fluid collection under the skin on the back of your baby’s neck. All babies have some nuchal translucency behind their necks, but many babies with Down’s syndrome have an increased amount, in addition to non-chromosomal abnormalities including genetic Di George syndrome and non genetic-Body-stalk anomaly.
- Two maternal blood (serum) tests – these blood tests monitor two substances in the blood of pregnant women:
- Pregnancy-associated plasma protein screening (PAPP-A) – a protein produced by the placenta in early pregnancy, abnormal levels tend to be associated with increased risk for chromosome abnormality.
- Human chorionic gonadotropin (hCG) – another production from the placenta is a hormone, with which abnormal levels are associated with chromosomal abnormality.
Typically these exams are combined when assessing the risk of chromosomal abnormality, the NT scan is completed at a diagnostic imaging facility, where if the proper measurements are obtained they will provide you with a diagnostic laboratory requisition to obtain your blood work. However, these tests do not provide a definite diagnosis. If the results are positive, genetic counseling is usually recommended, followed by more testing such as chorionic villus sampling (CVS), amniocentesis (a common nickname is amnio), or other ultrasounds for a more accurate diagnosis.
Second trimester screening tests can include several additional blood tests, called multiple markers. They provide more information on your risk of certain genetic conditions and birth defects. For the most accurate results, these additional blood tests are commonly collected at 16-18 weeks.
Multiple markers include:
Alpha-fetoprotein screening (AFP) – a protein typically produced in you baby’s liver and is present in the amniotic fluid that surrounds your baby and crosses the placenta into your blood. Abnormal AFP levels may signal to open neural tube defects (ONTD) such as spina bifida, down syndrome, and other abnormalities.
hCG – there is continual screening for hCG throughout your pregnancy.
Estriol & Inhibin – two hormones produced by the placenta.
It is important to remember that multiple markers are not diagnostic, meaning they’re not 100% accurate and typically only used as a screening test in order to inform physicians who requires further testing.
Amniocentesis is a procedure used to collect a small sample of the amniotic fluid that surrounds the fetus and is done to confirm diagnosis of chromosomal disorders and open neural tube defects. This test is typically offered between 15-20 weeks of pregnancy to those who have had positive screening results or are above 35 years of age.
This procedure involves inserting a long, thin needle through your pregnant belly into the amniotic sac to withdraw amniotic fluid for examination by a genetic lab. The fluid contains cells shed by the fetus and can be used for further genetic examination. If you are pregnant with twins or more multiples, it is required that a sample is collected from each amniotic sac.
Chorionic villus sampling (CVS) is a prenatal test involving the collection of a sample of placental tissue. It can be used for the same genetic testing as an amniocentesis, except for neural tube defects such as spina bifida. Thus, CVS is followed up by blood test between 16 and 18 weeks to screen for neural tube defects. CVS is typically performed between 10 and 13 weeks of pregnancy.
This procedure involves inserting a catheter, a small tube, through the vagina and into the cervix collecting cells. Similarly, with a multiple pregnancy, a sample needs to be collected from each placenta. It is important to note that CVS isn’t always feasible or successful with multiples. There are several scenarios where CVS is not feasible. Therefore, it is important to discuss your options with your doctor, as it is possible that a failed CVS could need a follow up amniocentesis.
Not all tests you undergo during your pregnancy involve screening for genetic or chromosomal disease, there are tests for gestational diabetes and of course normal pregnancy ultrasounds to asses that your baby is growing at the appropriate rate!
Remember that fetal ultrasounds have no known risks other than mild discomfort due to pressure from the transducer on the abdomen or in the vagina. No radiation is used during the procedure. Thus, all the initial screening procedures such as the nuchal translucency (NT) and blood screening you undergo at the beginning have no known risks and are all normal procedures that pregnant women usually undergo throughout their pregnancy. Any and all follow-up procedures are your choice. Therefore, discuss the options with your physician and decide based on estimated risk and your comfort level.