Prenatal Tests
Every parent-to-be spends happy hours envisioning a healthy baby. But these daydreams are often accompanied by moments of worry - what if the baby has a serious or untreatable health problem? What would I do? Would it be my fault? Concerns like these are completely natural, and some may be exaggerated by news stories about genetics and genetic testing, which promises that someday parents may be able to pick only "desirable" traits in their unborn children. With all the medical information available, you may feel as though you have to undergo a battery of prenatal tests to make sure your baby is healthy.
Prenatal tests can serve a useful function in terms of identifying, and sometimes treating, health problems that could endanger both you and your unborn child. However, they have limitations. As an expecting parent, you should take the time to educate yourself about these tests and to think about what you would do if a health problem is detected.
Why Are Prenatal Tests Performed?
Prenatal tests do several different things. They can identify:
treatable health problems in the mother that can affect the baby's health
characteristics of the fetus, 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 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 existing - they don't provide a definitive diagnosis. Other prenatal tests are diagnostic in nature, which means they can determine with a fair degree of certainty whether a fetus has a specific problem. Many women whose screening tests reveal the possibility of an abnormality have healthy babies, but in the interest of making the more specific determination, the screening test may be followed by a more invasive - and riskier - diagnostic test.
The issue of prenatal testing is further complicated by the fact that approximately 250 birth defects can be diagnosed in an unborn fetus - many more than can be treated or cured. This raises the question of what a parent will do once a defect or problem is detected.
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 suffers from gestational diabetes, her immunity to certain diseases, and 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. There are different categories of defects screened by prenatal tests, including:
Dominant gene disorders
In dominant gene disorders, 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 causing shorter-than- normal arms and legs
Huntingdon disease, a disease of the nervous system that causes neurologic deterioration affecting people in their 30s and 40s
Recessive gene disorders
Because there are so many genes in each cell, everyone carries some abnormal recessive genes, but most people don't have a defect because the normal gene overrules the abnormal one. But if a fetus has a pair of abnormal recessive genes (one from each parent), the child will have the disorder. It's more likely for this to happen in children born to certain ethnic groups or to parents who are blood relatives. Recessive gene disorders include:
cystic fibrosis (most common among people of northern European descent), a disease that causes the respiratory system to produce thick mucus that clogs the lungs
sickle cell disease (most common among people of African descent), a disease where red blood cells form a "sickle" shape, rather than the typical donut shape, get caught in blood vessels, and cut off oxygen to tissues
Tay-Sachs disease (most common among people of European [Ashkenazi] Jewish descent), a disorder causing mental retardation, blindness, seizures, and death
beta thalassemia (most common among people of Mediterranean descent), a disorder causing anemia
hip dislocations
