Prenatal Testing
Patients undergo a variety of tests while they are pregnant. Some of these tests are simple and easy to understand, but some are complex and difficult to interpret. The goal of this article is to help the expectant mother understand what tests are ordered and why, and to simplify the often complex nature of some of the testing one undergoes to assess the health and well being of the mother and fetus.
Maternal Testing
There are a few routine tests that every mother undergoes at the beginning of the pregnancy to assess her health and well being. Some are listed below. Remember, if you have a high-risk pregnancy, there may be certain other tests your doctor may order that are not included here.
Complete Blood Count/Blood Typing
These tests are designed to help your doctor assess if you have anemia (a low red blood cell count). If you are found to have anemia, it may be from a variety of causes (most likely low iron levels in your body), and your doctor may order some other tests to find out why you have anemia. Blood typing is done routinely to see if you are Rh positive or Rh negative. Some mothers who are Rh negative make certain proteins in their blood called antibodies that may harm the fetus. If you are Rh negative you may require an injection of "Rhogam" (a medicine that blocks the formation of these antibodies) at 28 weeks and at childbirth.
Pap Smear
This is done routinely at the beginning and end of every pregnancy. These tests allow the doctor to look for patients who may be at risk of developing cervical cancer.
Hepatitis/HIV/Syphilis
Two of these tests (hepatitis B and syphilis) are required by the Department of Health as they may cause damage to the fetus if unrecognized. HIV testing is required to be offered to all pregnant women, but it is not mandatory. All of these are done by a simple blood draw.
Fetal Tests
Triple Marker Screening
Usually done between 15-18 weeks, this test helps determine if your fetus is at risk for certain anatomical or chromosomal abnormalities (such as Down Syndrome). This test only tells you if your baby is at risk; it does NOT tell you if your baby has these conditions. The next few tests are more specific.
Ultrasound
Ultrasound uses sound waves to generate a picture of the baby. The technology of ultrasound is becoming so sophisticated that it can detect most major fetal anatomical abnormalities and allow doctors to see if the baby is at high or low risk for chromosomal syndromes as well. However, it cannot diagnose certain conditions, such as Down Syndrome, cystic fibrosis, or sickle cell anemia, which require more invasive testing.
Amniocentesis
This test is commonly offered to patients over the age of 35 and to those a doctor has determined to be at risk for a chromosome abnormality by ultrasound or the triple screen test. It is most commonly done at 15-18 weeks but can be done as early as weeks 12-13. The procedure involves placing a needle into the womb and withdrawing a small amount of amniotic fluid, which carries a small risk of miscarriage (1/250). This fluid is then used to determine how many chromosomes the baby carries (Down Syndrome babies have too many) and whether or not parts of the chromosomes have been deleted or moved. If you carry certain genes that put the baby at risk for conditions that run in your family (cystic fibrosis), more specific testing is done on these cells to see if the baby carries or has the disease. It also looks to determine if certain spinal abnormalities are present.
CVS (Chorionic Villus Sampling)
This test is done earlier than amniocentesis (9 ½ - 12 weeks) and determines much of the same information but does not determine if the baby has spinal abnormalities. It carries a slightly higher risk of miscarriage (1/100) and if done too early, has been associated with fetal damage, such as problems with limb development.
Non-Stress Testing
The fetal heartbeat should vary over a certain period of time (usually 20-40 minutes); variability helps your doctor determine if the baby is healthy inside the womb. If this test shows abnormalities, it sometimes will be followed by a biophysical profile or contraction stress test (below) which are more sensitive in evaluating fetal well being.
Biophysical profile
This test utilizes ultrasound to look at certain parameters of fetal health such as movement and amniotic fluid volume.
Contraction Stress Test
This test determines how the baby's heartbeat responds to artificially stimulated contractions. If the heartbeat drops with contractions, it may indicate that the baby is not getting enough oxygen in the womb.
All of the above tests help your doctor assess the health and well being of your baby. It must be stressed that the results of these tests must be interpreted in the context of the pregnancy. If the pregnancy is at higher risk than others, these tests may be utilized more frequently depending on their results. Also remember that most babies are born healthy and normal so even if you are undergoing some of these tests, it is just to assure you and your doctor that your baby is healthy.