Why Are Prenatal Tests Performed?
Every parent-to-be hopes for a healthy baby, but it can be hard not to worry: What if the baby has a serious or untreatable health problem? What would I do? Is there anything I can do to prevent problems?
Concerns like these are completely natural. Fortunately, though, a wide array of tests for pregnant women can help to reassure them and keep them informed throughout their pregnancies.
Prenatal tests can help identify health problems that could endanger both you and your unborn child, some of which are treatable. However, these tests do have limitations. As an expectant parent, it's important to educate yourself about them and to think about what you would do if a health problem is detected in either you or your baby.
Why Are Prenatal Tests Performed?
Prenatal tests can identify several different things:
· treatable health problems in the mother that can affect the baby's health
· characteristics of the baby, including size, sex, age, and placement in the uterus
· the chance that a baby has certain congenital, genetic, or chromosomal problems
· certain types of fetal abnormalities, including some heart problems
The last two items on this list may seem the same, but there's a key difference. Some prenatal tests are screening tests and only reveal the possibility of a problem. Other prenatal tests are diagnostic, which means they can determine — with a fair degree of certainty — whether a fetus has a specific problem. In the interest of making the more specific determination, the screening test may be followed by a diagnostic test.
Prenatal testing is further complicated by the fact that more abnormalities can be diagnosed in a fetus than can be treated or cured.
What Do Prenatal Tests Find?
Among other things, routine prenatal tests can determine key things about the mother's health, including:
· her blood type
· whether she has gestational diabetes
· her immunity to certain diseases
· whether she has a sexually transmitted disease (STD) or cervical cancer
All of these conditions can affect the health of the fetus.
Prenatal tests also can determine things about the fetus' health, including whether it's one of the 2% to 3% of babies in the United States that the American College of Obstetricians and Gynecologists (ACOG) says have major congenital birth defects.
Tests for Disorders
Categories of defects which can be picked up by prenatal tests include the following disorders:
Dominant Gene Disorders
In dominant gene disorders when one parent is affected, there's a 50-50 chance a child will inherit the gene from the affected parent and have the disorder.
Dominant gene disorders include:
· Achondroplasia, a rare abnormality of the skeleton that causes a form of dwarfism, can be inherited from a parent who has it, but most cases occur without a family history.
· Huntington disease, a disease of the nervous system that causes a combination of mental deterioration and a movement disorder.
Who Has Prenatal Tests?
Certain prenatal tests are considered routine — that is, almost all pregnant women receiving prenatal care get them. Other nonroutine tests are recommended only for certain women, especially those with high-risk pregnancies. These may include women who:
· are age 35 or older
· are adolescents
· have had a premature baby
· have had a baby with a birth defect — especially heart or genetic problems
· are carrying more than one baby
· have high blood pressure, diabetes, lupus, heart disease, kidney problems, cancer, a sexually transmitted disease,asthma, or a seizure disorder
· have an ethnic background in which genetic disorders are common (or a partner who does)
· have a family history of mental retardation (or a partner who does)
Although your health care provider (which may be your OB-GYN, family doctor, or a certified nurse-midwife) may recommend these tests, it's ultimately up to you to decide whether to have them.
Also, if you or your partner have a family history of genetic problems, you may want to consult with a genetic counselor to help you look at the history of problems in your family, and to determine the risk to your children.
To decide which tests are right for you, it's important to carefully discuss with your health care provider:
· what these tests are supposed to measure
· how reliable they are
· the potential risks
· your options and plans if the results indicate a disorder or defect
Prenatal Tests During the First Visit
During your first visit to your health care provider for prenatal care, you can expect to have a full physical, which may include a pelvic and rectal examination, and you'll undergo certain tests regardless of your age or genetic background.
You may have a urine test to check for protein, sugar, or signs of infection.
Blood tests check for:
· your blood type and Rh factor. If your blood is Rh negative and your partner's is Rh positive, you may develop antibodies that prove dangerous to your fetus. This can be prevented through a course of injections given to you.
· anemia (a low red blood cell count)
· hepatitis B, syphilis, and HIV
· immunity to German measles (rubella) and chickenpox(varicella)
· cystic fibrosis. Health care providers now routinely offer this screening even when there's no family history of the disorder.
Cervical tests (also called Pap smears) check for:
· STDs such as chlamydia and gonorrhea
· changes that could lead to cervical cancer
To do a Pap smear, your health care provider uses what looks like a very long mascara wand or cotton swab to gently scrape the inside of your cervix (the opening to the uterus that's located at the very top of the vagina). This may be a little uncomfortable, but it is over quickly.
After the initial visit, your health care provider will order other tests based on, among other things, your personal medical history and risk factors, as well as the current recommendations. These tests may include:
· Urine tests for sugar, protein, and signs of infection. The sugar in urine may indicate gestational diabetes — diabetes that occurs during pregnancy; the protein can indicate preeclampsia — a condition that develops in late pregnancy and is characterized by a rise in blood pressure, with fluid retention and protein in the urine.
· Group B streptococcus (GBS) infection. GBS bacteria are found naturally in the vaginas of many women but can cause serious infections in newborns. This test involves swabbing the vagina and rectum, usually between the 35th and 37th weeks of pregnancy. If the test comes back positive, it is important to go to the hospital as soon as your labor begins so that intravenous antibiotics can be started in order to reduce the chance of the baby being infected.
· Sickle cell trait tests for women of African or Mediterranean descent, who are at higher risk for having sickle cell anemia — a chronic blood disease — or carrying the trait, which can be passed on to their children.
Here are some other tests that might be performed during pregnancy:
In this test, sound waves are bounced off the baby's bones and tissues to construct an image showing the baby's shape and position in the uterus. Ultrasounds were once used only in high-risk pregnancies but have become so common that they're often part of routine prenatal care.
Also called a sonogram, sonograph, echogram, or ultrasonogram, an ultrasound is used:
· to determine whether the fetus is growing at a normal rate
· to verify the expected date of delivery
· to record fetal heartbeat or breathing movements
· to see whether there might be more than one fetus
· to identify a variety of abnormalities that might affect the remainder of the pregnancy or delivery
· to make sure the amount of amniotic fluid in the uterus is adequate
· to indicate the position of the placenta in late pregnancy (which may be blocking the baby's way out of the uterus)
· to detect pregnancies outside the uterus
· as a guide during other tests such as amniocentesis
Ultrasounds also are used to detect:
· structural defects such as spina bifida and anencephaly
· congenital heart defects
· gastrointestinal and kidney malformations
· cleft lip or palate
Most women have at least one ultrasound. The test is considered to be safe. Some women will have multiple ultrasounds during the pregnancy, others do not have any. Ask your health care provider if he or she thinks you will have ultrasounds during your pregnancy.
An ultrasound is usually performed at 18 to 20 weeks to look at your baby's anatomy. If you want to know your baby's gender, you may be able to find out during this time — that is, if the genitals are in a visible position.
Ultrasounds also can be done sooner or later and sometimes more than once, depending on the health care provider and the pregnancy. For example, some providers will order an ultrasound to date the pregnancy, usually during the first 3 months. And others may want to order one during late pregnancy to make sure the baby's turned the right way before delivery.
Women with high-risk pregnancies may need to have multiple ultrasounds using more sophisticated equipment. Results can be confirmed when needed using special three-dimensional (3-D) equipment that allows the technician to get a more detailed look at the baby.
Women need to have a full bladder for a transabdominal ultrasound (an ultrasound of the belly) to be performed in the early months — you may be asked to drink a lot of water and not urinate. You'll lie on an examining table and your abdomen will be coated with a special ultrasound gel. A technician will pass a wand-like instrument called a transducer back and forth over your abdomen. You may feel some pressure as the technician presses on the bladder. High-frequency sound waves "echo" off your body (and the fetus) and create a picture of the fetus inside on a computer screen.
You may want to ask to have the picture interpreted for you, even in late pregnancy — it often doesn't look like a baby to the untrained eye.
Sometimes, if the technician isn't able to see a good enough image from the ultrasound, he or she will determine that a transvaginal ultrasound is necessary. This is especially common in early pregnancy. For this procedure, your bladder should be empty. Instead of a transducer being moved over your abdomen, a slender probe called an endovaginal transducer is placed inside your vagina. This technique often provides improved images of the uterus and ovaries.
Some health care providers may have the equipment and trained personnel necessary to provide in-office ultrasounds, whereas others may have you go to a local hospital or radiology center. Depending on where you have the ultrasound done, you may be able to get a printed picture (or multiple pictures) of your baby and/or a disc of images you can view on your computer and even send to friends and family.
Although the technician can see the images immediately, a full evaluation by a physician may take up to 1 week.
Depending on where you have the ultrasound done, the technician may be able to tell you that day whether everything looks OK. However, most radiology centers or health care providers prefer that technicians not comment until a specialist has taken a look — even when everything is OK.
Glucose screening checks for gestational diabetes, a short-term form of diabetes that develops in some women during pregnancy. Gestational diabetes is increasing in frequency in the United States, and may occur in 3 to 8% of pregnancies. Gestational diabetes can cause health problems for the baby, especially if it is not diagnoses or treated.
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