Definition, Purpose, Precautions, Description
Antenatal testing includes any diagnostic procedures performed before the birth of a baby.
These tests and exams are essential for protecting the health of a pregnant woman and her developing child.
Some tests, such as amniocentisis, carry a small risk of a miscarriage or other complications that could harm the mother or baby.
Women who become pregnant undergo a wide variety of tests throughout the nine months before delivery. In the early stages, physicians order blood tests to screen for possible disorders or infections, such as human immunodeficiency virus (HIV), which can pass from the mother to the fetus. Later, the focus shifts to checking on fetal well-being with a variety of technological tools such as ultrasound scans. Descriptions of the most common tests and procedures used during pregnancy are listed below.
When a woman first learns she is pregnant, her physician will run a series of routine urine and blood tests to determine her blood type, check for anemia and gestational diabetes, make sure she is immune to rubella (German measles) and check for infectious diseases like HIV, hepatitis, chlamydia or syphilis. Physicians also usually do pelvic exam to screen for cervical cancer and check the patient's blood pressure. As the pregnancy progresses, more tests will follow.
Ultrasound is a device that records sound waves as they bounce off the developing fetus to create an image, which is projected onto a large computer screen. Physicians order an ultrasound scan to listen for a fetal heartbeat, determine a woman's precise due date and check for twins, among other uses. An ultrasound scan also is known as a sonogram. The procedure takes a few minutes, is painless and usually is covered by health insurance.
The ultrasound technician will ask the pregnant woman to remove her clothes and change into a gown. The technician may rub some gel on the woman's stomach, which helps the hand-held device pick up sound waves better. In certain cases, the technician may insert a plastic probe into the woman's vaginal canal to get a clearer picture of the fetus. Early in pregnancy, the test may need to be done with a full bladder.
Unlike x rays, ultrasound is safe to use during pregnancy. It does not cause any known side-effects that would harm the mother or baby.
Pregnant women usually will have their first ultra-sound anytime between 8 and 12 weeks of gestation. In normal cases, the technician is able to identify a fetal heartbeat, which appears as a flashing light on the screen. Closer to the due date, physicians use ultrasound to make sure the fetus is in the correct position to exit the birth canal head first.
Sometimes an ultrasound will show that a fetus has stopped growing, or a gestational sac has formed without a fetus, and a miscarriage has occurred. Later in pregnancy, it also may show that the child is in a breech position, oriented feet first, which can cause a difficult labor.
Tests for birth defects
Most obstetricians offer parents a variety of ways to find out if their developing child might have birth defects such as spina bifida and Down Syndrome. An alpha fetoprotein screen can be done through a simple blood test in the doctor's office between the 16th and 18th week of gestation. It tells the odds that their child will have a severe congenital anomaly. The test works by measuring the level of alpha fetoprotein, a substance produced by a fetus with birth defects. Low levels of alpha fetoprotein in the mother's blood may indicate Down's Syndrome. In that case, the next step for most couples is amniocentesis because the alpha fetoprotein test can give false-positive results. Amniocentesis is a more accurate test, but it also has higher risks of complications.
This procedure typically is used to diagnose Down syndrome while a developing child is still in the womb, at 15-28 weeks.
During amniocentesis, a doctor inserts a needle through a woman's vaginal canal and inside her cervix. Using ultrasound as a guide, the doctor pierces the uterus to withdraw a sample of fluid from the amniotic sac. Afterwards, tiny cells shed by the fetus can be studied in the laboratory. Scientists can analyze DNA samples to determine if the fetus has Down syndrome or other genetic conditions. Amniocentesis also can determine the sex of the fetus.
Women who have a history of recurring miscarriages may not want to have this procedure.
Amniocentesis is usually performed in a doctor's office on an outpatient basis.
Common side effects include cramping and bleeding.
In about one out of every 1,000 cases, amniocentesis causes a needle to puncture the uterine wall, which could result in miscarriage.
In most cases, couples find out their baby does not have a birth defect.
If the results come back positive for Down's Syndrome or other serious conditions, the couple must decide if they want to end the pregnancy. Others use the knowledge to plan and prepare any special care needed for their future child.
Group B Strep
This test is for Group B streptococci (GBS) infection.
By testing for GBS, physicians can determine if a woman is at risk of passing this infection along to her child.
Women who have had a prior child with GBS, or who have a fever or prolonged or premature rupture of the amniotic sac may be at higher risk for this type of infection.
GBS is a type of bacteria commonly found in the vagina and rectum. Unlike regular strep throat, GBS can be present in a person's body without causing any symptoms, so many women do not realize they are infected with it.
To test for the presence of GBS, doctors may take a urine sample. They also may collect samples from the vagina or rectum, which are then analyzed in a lab. This test is usually performed late in pregnancy, at 35-37 weeks of gestation.
This is a routine urine test or pelvic exam with no side effects.
In many cases, doctors do not find any evidence of this type of infection.
If a woman is found to be infected with Group B strep, physicians usually wait to treat it until just before labor begins. At that time, they may give the mother antibiotics so the baby is not born with the infection. Newborns who are exposed to Group B strep can have inflammation of the brain, spinal cord, blood or lungs. In some cases, this serious complication can result in infant death.
Eisenberg, Arlene, et al. What to Expect When You're Expecting New York: Workman Publishing Company Inc, 1996. Planning your Pregnancy and Birth Washington, DC: The American College of Obstetricians and Gynecologists, 2000.
Parkey, Paula. "Birth Defects: Is Prenatal Screening Advisable?" CBS Health Watch (April, 2000). <http://www.cbshealthwatch.com/cx/viewarticle/214798>.
American College of Obstetricians and Gynecologists.409 12th Street SW, Washington, DC 20024-2188. (202) 638-5577. <http://www.acog.org>.
March of Dimes Birth Defects Foundation. P.O. Box 1657, Wilkes-Barre, PA 18703. 1-800-367-6630. <http://www.modimes.org>.
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