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 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)
· 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.
· 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 (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.
· 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
· structural defects such as spina bifida and anencephaly
· congenital heart defects
· gastrointestinal and kidney malformations
· cleft lip or palate
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