Prenatal Tests
Prenatal tests can determine a variety of things about the overall health of a mother and her unborn baby. Certain tests are routine and almost all pregnant women get these tests as part of their prenatal care. Routine prenatal tests can include; Rhesus test, hemoglobin check, gonorrhea test, syphilis test, chlamydia test, rubella testing, human immunodeficiency virus counseling and testing (HIV), glucose tolerance test, and hepatitis B virus screening. All are usually performed during the first prenatal visit along with blood and urine samples and a Pap smear, and then periodically checked during routine prenatal visits.
Other prenatal tests can tell a lot about an unborn baby’s health, specifically whether he or she has a genetic defect or other birth defects. Some common tests used to help screen for chromosomal abnormalities or other birth defects are amniocentesis, alpha-fetoprotein (AFP), maternal serum triple screen, chorionic villus sampling (CVS), percutaneous umbilical blood sampling (PUBS), non-stress testing (NST), ultrasound (a.k.a. a sonogram), and a biophysical profile (BPP) exam.
Annotated Prenatal Tests List
What are prenatal tests? You can review the list of prenatal tests here, with brief explanations about each.
■ Rhesus Test as one of the Prenatal tests:
The Rhesus (Rh) test determines whether you have Rh-negative or Rh-positive blood. Eight to fifteen percent of pregnant women have Rh-negative blood. Having Rh-negative blood does not necessarily mean there will be problems with the pregnancy. Having Rh-negative blood is only of concern if your baby has Rh-positive blood, a possibility if the baby’s father is Rh-positive. In all pregnancies, a small amount of the baby’s blood may mix with yours. If there is a mismatch for Rh (yours is negative, the baby’s blood is positive) your baby may develop antibodies-proteins in the blood that can attack Rh-positive cells. If you have Rh-negative blood, your doctor will need to check your blood periodically throughout your pregnancy for antibodies like this that your body may manufacture to “defend” itself if your baby has Rh-positive blood. Rh incompatibility is not usually a danger in first pregnancies because Rh-negative mothers do not usually build antibodies (or become sensitized) to Rh-positive blood until the birth of their first Rh-positive baby. There is a danger, however, if the mother has an Rh-positive fetus in later pregnancy, because the antibodies already present may attack the fetal blood cells. To prevent problems, an injection of a substance called Rh immune globin (RhoGAM) should be given at 28 weeks of pregnancy to all Rh-negative pregnant women and after the baby is delivered. This injection will substantially reduce the risk that the antibodies will develop at all. If you have any questions about the Rh factor or think you should have received Rh immune globin but did not, talk to your healthcare provider.
■ Hemoglobin Check as one of the Prenatal tests:
Hemoglobin levels are checked to determine whether you have a low red blood cell count or anemia, which is common in pregnant mothers. Whether you have anemia or not, your obstetrical care provider will probably prescribe or recommend an iron supplement or prenatal vitamin containing iron, because there is an increased need for iron in pregnancy. These Iron supplements, however, may cause your bowel movements to turn black. Prenatal vitamins may also cause constipation. This constipation can often be avoided by drinking plenty of fluids, exercising, and eating fiber-rich foods such as bran, fruits, and leafy vegetables. Consult with your doctor to discuss additional treatments if constipation persists.
■ Gonorrhea Test as one of the Prenatal tests:
This sexually transmitted disease (STD) can cause infertility, blindness, arthritis, and damage to the urinary tract. It can also cause an eye condition in your newborn called gonococcal conjunctivitis that can result in blindness if untreated. A woman who tests positive for gonorrhea can usually be safely and successfully treated with antibiotics. Most newborns routinely receive antibiotic ointment under their eyelids immediately after birth to prevent blindness that can be caused by gonococcal conjunctivitis.
■ Syphilis Test as one of the Prenatal tests:
Every pregnant woman is required to have a serology or blood test for syphilis. Syphilis is a sexually transmitted disease that can spread through the body and cause heart disease, neurological disorders, and death. During pregnancy, it can cause miscarriage, stillbirth, or abnormalities in the fetus such as anemia and damage to the nervous system, bones, liver, and teeth. These complications of syphilis can usually be avoided if the disease is detected and treated in early pregnancy.
■ Chlamydia as one of the Prenatal tests:
Chlamydia is the most common sexually transmitted disease in the United States. Without treatment, chlamydia can spread from the cervix to the fallopian tubes and ovaries and cause pelvic inflammatory disease, which can result in sterility. During pregnancy, chlamydia may cause premature delivery, miscarriage, or stillbirth. Babies who are born to infected mothers may develop pneumonia, ear infections, and eye infections, which can result in blindness. Chlamydia can be diagnosed with a cervical exam and an examination of cells taken from the cervix, and can usually be safely treated with antibiotics.
■ Rubella Testing as one of the Prenatal tests:
Testing for rubella (German measles) determines whether you are resistant to the disease. Most women are resistant because they have been vaccinated during childhood (rubella is the “R” in MMR injections.) If you are not, your doctor will advise you to avoid contact with anyone who has German measles during your pregnancy. This should not be difficult because vaccination has made German measles uncommon. Exposure alone does not mean you will pick up the infection, but if infection occurs during the first trimester, there is a risk of congenital defects developing in your baby. If you do not have protection against rubella, your doctor will probably advise you to have a rubella vaccination immediately after your pregnancy in order to avoid any danger from exposure during future pregnancies. This vaccination will help protect you from rubella. Although you will be advised to wait two to three months before becoming pregnant again after having the rubella vaccination, there is no evidence that rubella vaccination in pregnancy is harmful.
■ Human Immunodeficiency Virus Counseling and Testing (HIV)
Human immunodeficiency virus (HIV) is the virus that causes acquired immune deficiency syndrome (AIDS). AIDS destroys the body’s ability to fight infections. There is no cure for HIV or AIDS, but treatment can help women and men with HIV lead long and productive lives. HIV is spread through contact with infected body fluids (blood, semen, vaginal fluid). Your obstetrical care provider will talk to you about risk factors for HIV and ask you if you want to be given an HIV blood test. It is recommended that all pregnant women have an HIV test, no matter what their risks or how recently they have been tested. It is very important for you to consider being tested for HIV because pregnant women who have HIV or AIDS can pass the infection on to their babies. If you test positive for HIV, there are drugs your doctor can prescribe that can slow down the effects of the virus in your baby and reduce the chance that your baby will be infected with HIV.
■ Hepatitis B Virus Screening as one of the Prenatal tests:
Hepatitis B is a virus that attacks and damages the liver. It is spread through contact with infected body fluids (blood, semen, vaginal fluids, and saliva). People considered at high risk for hepatitis B virus (HBV) include healthcare workers, those who have multiple sex partners, have had a sexually transmitted disease, those who have injected illegal drugs, or people who have received a blood transfusion or dialysis. Pregnant women can be tested for HBV with a simple blood test. According to The American College of Obstetricians and Gynecologists, if you have not been infected but think you might be at risk of contracting HBV, you can be given a vaccination against HBV that is safe to receive during pregnancy. If you test positive for HBV, your baby will most likely also be given HBV immunoglobulin shortly after birth to reduce the risk of infection, as well as the HBV vaccine.
■ Chorionic Villus Sampling (CVS) as one of the Prenatal tests:
One alternative to amniocentesis is chorionic villus sampling (CVS). The chorionic villi are part of the tissues which surround the fetus and become the placenta. A sample of chorionic villi is taken either vaginally or through the abdomen in the same manner as amniocentesis.
This method is not for everyone, but it should be considered by anyone who wants prenatal testing results as early as possible in pregnancy. CVS can be carried out anytime from the 10th through the 12th week of pregnancy. CVS provides accurate diagnostic information, and the risk to pregnancy is about equal to the risks posed by amniocentesis. However, a mixture of the mother’s and fetus’s cells may inadvertently be withdrawn during CVS resulting in an inaccurate diagnosis.
■ Maternal Serum Triple Screen as one of the Prenatal tests:
The maternal serum triple screen is a general term for a blood test known by several brand names such as AFP-3, Triscreen, Downscreen Plus, Trisomy Profile, AFP Plus, etc. This is a screening test used in pregnancy to help identify pregnancies at increased risk for certain birth defects. Knowledge of these birth defects may change pregnancy management for you and your healthcare provider. There are two main types of birth defects for which the test screens: Down syndrome and neural tube defects (spina bifida and anencephaly). These are usually not inherited, and occur unexpectedly.
The test is drawn between 15 and 20 weeks of pregnancy. Correct gestational age is extremely important in the interpretation of the test. The laboratory measures the levels of three chemicals in the mother’s blood which are made either by the fetus or the placenta during pregnancy. These levels, along with information about the mother and the pregnancy, are used to calculate the risk for Down syndrome and spina bifida.
It is important to understand that the blood test is a screening test, not a diagnostic test. It cannot tell if the abnormality is present or not. Research has shown that in approximately 80-90% of pregnancies where a neural tube defect is present, the blood test will be abnormal and the patient will be offered an opportunity to consider further diagnostic testing. This means that the test can detect the majority of cases of Down syndrome and spina bifida but it cannot detect all of them. It is important to remember that most women who receive an abnormal screening result go on to have normal, healthy babies. However, a genetic consultation/evaluation is recommended to review your individual blood test results and to discuss the risk which has been identified in your pregnancy.
The types of further diagnostic testing which are available and applicable to your situation will be discussed, including their risks, benefits, and limitations. Such further diagnostic options may include high-resolution ultrasound, amniocentesis, or both, depending on your situation. It will be your decision whether or not to proceed with further diagnostic testing. The genetic counselor will also review your family medical history and pregnancy history in order to determine whether other risk factors are present, and will help to clarify your concerns and answer your questions.
■ Percutaneous Umbilical Blood Sampling (PUBS) as one of the Prenatal tests:
Percutaneous umbilical blood sampling (PUBS) or fetal blood sampling is a procedure indicated in certain high-risk situations. A small sample of fetal blood is withdrawn through a slender needle passed through the woman’s abdomen into the baby’s umbilical cord. Although the procedure is similar to amniocentesis for the woman, it requires a high level of expertise by those performing and assisting in the procedure. It is available in a limited number of high-risk pregnancy centers. PUBS is generally performed after the 18th week of pregnancy. The timing depends on the reason the test is being done. A brief period of observation and special preparation may be suggested for procedures done after the 24th week of pregnancy.
The risk to the pregnancy is greater than for other prenatal procedures, therefore, PUBS is reserved for those pregnancies in which the information required about the fetus (fetal blood type, fetal anemia, infection, etc.) cannot be obtained accurately, completely, and/or insufficient time to benefit pregnancy management by other prenatal diagnostic procedures.
■ Alpha-Fetoprotein (AFP) as one of the Prenatal tests:
Alpha-fetoprotein (AFP) is a type of protein produced only by a fetus or the fetal yolk sac. The mother-to-be does not produce this substance on her own. Screening for AFP involves analyzing the level of the protein in the mother’s blood. The test is generally performed between the 16th and 18th weeks of pregnancy.
An excessive amount of AFP in your blood could indicate that the baby has a neural tube defect such as the spinal deformity known as spina bifida. There could also be a high AFP reading if more than one fetus is producing the alpha-fetoprotein. An elevated level may also indicate that the pregnancy is more advanced than the initial estimate. An abnormally low amount of AFP may point to the possibility of Down syndrome or another chromosomal problem.
It is important to remember that this is only a screening test. It is not a diagnostic procedure. AFP testing will not tell you for sure that something is wrong, but rather, that the matter should be pursued further. For example, if a second AFP test also showed low AFP levels, you would be advised to have an amniocentesis to rule out the possibility of Down syndrome.
The AFP test itself is safe. However, if the test falsely indicates that there may be a problem when everything is really fine, the mother and baby could then be exposed to the unnecessary risk of a more invasive procedure.
■ Glucose Tolerance Test as one of the Prenatal tests:
The glucose tolerance test (GTT) is routinely administered to pregnant women between the 24th and 28th week of pregnancy. It tests for gestational diabetes, a form of diabetes that is not the same as diabetes but is a condition that develops in some women due to hormonal changes during pregnancy. Women with gestational diabetes have higher blood sugars, are at risk for having larger babies, and have an increased risk of developing diabetes later in life. To conduct this test, your obstetrical care provider will give you a standard drink containing sugar (it’s like a very sweet soda). A short time later, your blood sugar level will be measured by drawing your blood. A high blood sugar level does not necessarily mean that you have gestational diabetes. It does mean, however, that additional testing is needed.
■ Ultrasound or Sonogram as one of the Prenatal tests:
Ultrasound, or sonography, uses sound waves to create a picture of the fetus. Very early in pregnancy, it can be used to confirm pregnancy and determine the actual age of the fetus, the location of the fetus, and the number of fetuses. During the later stages of pregnancy, an ultrasound can be used to see the baby’s organs and central nervous system and make sure the baby is growing at a rate appropriate for that stage of the pregnancy. It can detect some but by no means all, birth defects. While the benefits of having a routine ultrasound are controversial, many women have them for reassurance that all seems normal. If you have an ultrasound, you will be able to watch the baby as it moves on the screen, and perhaps take home a somewhat dark and fuzzy, but still fascinating, sonographic image of the newest family member.
■ Amniocentesis as one of the Prenatal tests:
If either the blood test or the ultrasound indicates a possible problem, your doctor might suggest further testing. For 20 years, amniocentesis has been the primary method available for the assessment of the developing fetus. While blood tests can detect elevated levels of certain substances, amniocentesis actually tests for abnormalities in the fetus’s chromosomes.
During amniocentesis, the physician uses a thin needle to remove about three teaspoons of the amniotic fluid surrounding the fetus. That fluid is then tested to make sure its cells contain normal chromosomes. Some couples have an amniocentesis to test for inherited diseases such as cystic fibrosis, Tay-Sachs disease, and sickle cell disease. Amniocentesis can also detect severe defects of the head and spinal column.
Amniocentesis poses a small risk to the pregnancy, but serious complications are extremely rare. The physician uses an ultrasound as a visual guide during the whole procedure to prevent the needle from touching the fetus. The most serious risk of amniocentesis is a miscarriage, which happens in about one of every 200 cases.
■ Non-Stress Testing (NST) as one of the Prenatal tests:
Non-stress testing (NST) uses an electronic fetal monitor to monitor the fetal heart rate. Test results help reassure you and your practitioner about the health of the pregnancy. This test is often recommended for women with diabetes or high blood pressure, those who are carrying more than one fetus, or women with other complications of pregnancy. It may also be used if your pregnancy goes a week or more past your due date.
■ Biophysical Profile (BPP) as one of the Prenatal tests:
The biophysical profile (BPP) uses ultrasound, perhaps together with non-stress testing, to evaluate a fetus’s well-being. BPP looks at the movement of the fetal diaphragm or fetal breathing, body movements, muscle tone, and the amount of amniotic fluid. The test is used in many of the same situations as non-stress testing. Your provider can help you understand why he or she has selected one particular test.
