Prenatal testing encompasses a wide array of procedures from abdominal ultrasound to more invasive procedures such as amniocentesis.

While the conception and growth of a new life is one nature’s most phenomenal processes, occasionally, problems in either fetal development or maternal changes occur without warning. Fortunately for some, medical technology continues to advance such that many expectant parents have the advantage of detecting any maternal or fetal challenges before their expected due dates, often accompanied by the ability to treat, control, and often cure, certain conditions.

Prenatal testing encompasses a wide array of procedures from abdominal ultrasound to more invasive procedures such as amniocentesis. Many prenatal tests, including various types of blood lab analyses, are done in specific stages of pregnancy as a matter of routine, while others are indicated when the presence of a specific condition is suspected.

The most common types of prenatal tests include the following:

Ultrasound (“U/S” or “Sonogram”)
While opinions surrounding necessity of routine prenatal ultrasound varies between medical practitioners, many women will undergo this non-invasive procedure as a matter of course between the 16th and 20th weeks of pregnancy. An abdominal ultrasound is a procedure using a device that releases sound waves that, when placed on the abdomen of a pregnant woman, bounce off of internal tissues and organs, producing visual images of the uterus, placenta, the fetus itself, as well as the fetal heartbeat. These images can be seen by both the technician and the patient on a monitor and, although often difficult to distinguish by the patient, can be evaluated by a trained eye. In many cases, the images are clear enough that the gender of the developing fetus can be determined. Ultrasounds can also be done vaginally using a thin probe, most commonly in early pregnancy, as an alternative to abdominal ultrasound.

Ultrasounds are generally used as a prenatal testing means to check fetal heart rate, amniotic fluid levels, determine fetal age, detect any abnormalities in physical development, or to diagnose the presence a pregnancy with more than one fetus. There has been some controversy among the medical community as to the safety of routine ultrasound, particular those done in repetition throughout pregnancy, however, most research shows ultrasound to be a generally safe procedure for both mother and baby.

Glucose Tolerance Test (“GTT”)
A non-invasive prenatal screening procedure that tests for the presence of gestational diabetes, a condition which can affect the fetal blood sugar levels and result in an abnormally rapid weight gain, often making the infant too large to pass through the birth canal during delivery. Although this test is offered to most pregnant patients, it is most often recommended for those who have a family history of diabetes or a history of gestational diabetes, or those who are obese during pregnancy. During this test, the patient is asked to drink 8 ounces of a prescribed glucose solution. After a period of time, her blood is drawn, by which glucose levels are tested and a determination is made as to whether or not gestational diabetes is present. Most often, the condition can be controlled by a modified diet, although some will require insulin treatment. In any event, gestational diabetes is usually a temporary condition that resolves after delivery.

Alpha-Fetoprotein (“AFP”), AFP+ and Triple Screen Tests (“Maternal Serum Screening”)
An optional test offered to most pregnant women between the 15th and 20th weeks of pregnancy, this non-invasive blood screening refers to a series of tests that can detect a patient’s risk of delivering an infant with certain neural tube or chromosomal defects. Once maternal blood is drawn, it is tested to measure levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), or unconjugated estriol (UE3) alone, or a combination of two or all three.

AFP, HCG and UE3 are substances all found in the blood of pregnant women and are produced by the fetus and placenta. If AFP and HCG levels alone are tested, it is commonly referred to as the “AFP +” test. If AFP, HCG and UE3 are all tested, it is known as the “triple screen,” the grouping of tests that are thought to be the most accurate of the three. Though the AFP tests are not diagnostic in nature (i.e. they don’t provide a definitive diagnosis) and measure only one’s risk of a problem, AFP levels that are found to be elevated can be an indication of certain fetal abnormalities or, in some cases, the presence of an undiagnosed multiple pregnancy. The primary disadvantage to the AFP test is its high percentage, nearly 50%, of false-positive results. Many women who receive a positive AFP result are, in reality, carrying healthy, normal fetuses, though most will be advised to undergo amniocentesis to confirm or rule out the initial risk diagnosis.

Chorionic Villous Sampling (“CVS”)
Most often offered to women 35 or older or those at higher risks for having a baby with certain birth defects, CVS is either done by inserting a long needle guided by ultrasound through the abdomen into the placenta, or by inserting a tube into the cervix. By either method, fluid and cells are drawn from the placenta and evaluated by a lab technician to check for any fetal abnormalities. CVS, one of the more invasive prenatal tests, carries a slight risk of fetal limb injury or miscarriage.

Amniocentesis
Usually recommended for or offered to pregnant women over 35 or those with a family history of birth defects, this procedure involves inserting a long, fine needle through the abdomen and into the uterus, after which the amniotic fluid is drawn and tested in a lab. Amniocentesis can detect certain fetal abnormalities and neural tube defects, such as spina bifida, down syndrome, and anencephaly. Amniocentesis can also definitively detect the gender of an unborn baby, though it is never done for this purpose alone. Like other invasive prenatal tests, amniocentesis carries a higher risk of miscarriage.

Non-Stress Test
Typically performed in the late stages of pregnancy, the non-stress test is used to determine overall fetal health and, in some cases, its ability to survive outside of the womb should early induction be a possible indication. The patient is generally seated with an external fetal heart rate monitor strapped around her abdomen and asked to press a button attached to the monitor each time a fetal movement is felt to record activity. If the fetal heart rate accelerates each time movement occurs, the test is considered normal. If the heart rate does not accelerate with recorded movement, external stimulation (i.e. noise, rubbing the mother’s abdomen, etc.) may be performed to “wake” a sleeping fetus and, if no change occurs with stimulation, further tests to check fetal well being may be recommended.

Group B Strep (“GBS”) Test
An important, non-invasive prenatal screen, the GBS test can detect a common maternal infection known as Group B Strep, which can be transmitted to an infant during labor and delivery. Many practitioners agree that all women should be tested for GBS in the late 3rd trimester to rule out the condition, as GBS can cause severe illness in an affected newborn, including vision and/or hearing loss, and even death. The presence of GBS is tested simply by swabbing the vagina and/or rectum of the patient and testing the sample for the presence of the infection. In most cases, if GBS is detected, antibiotics are administered via IV during labor and delivery to prevent transmission and in some hospitals, antibiotics are given as a preventative measure.

As overwhelming as it can appear, most prenatal diagnostic tests are performed by specific indication or risk factors only. If you have any questions about prenatal tests offered during pregnancy, ask your health care provider for further information, accuracy statistics, or for written material on each test.

Tonja Brossette, staff writer for BabyUniversity, is a happily married, stay-at-home-mother to her two children, Keaton and Keller. As a published freelance writer, the focus of her content primarily encompasses parenting and child care issues, as well as the miraculous process of preconception, pregnancy & childbirth. Tonja can be contacted at tonja@babyuniversity.com