Prenatal tests can help identify health problems that could endanger both a woman her 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 to think about what you would do if a health problem was detected in either you or your baby.

Prenatal tests are given in thefirst, second, and thirdtrimesters. In a mother, they can determine key things about her health that can affect her baby's health, such as: 

• her blood type

• whether she has gestational diabetes, anemia, or other health conditions

• her immunity to certain diseases

• whether she has a sexually transmitted disease (STD) or cervical cancer

 In a developing child, prenatal tests can identify:

• treatable health problems that can affect the baby's health

• characteristics of the baby, including size, sex, age, placement in the uterus

• the chance that a baby has certain birth defects or genetic problems

• certain types of fetal abnormalities, like 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 only reveal the possibility of a problem. Other prenatal tests arediagnostic, which means that 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.