Many parents assume that all birth defects are severe or even fatal, but the fact is that many are treatable, often immediately after birth - and sometimes even before the baby is born. It's especially important to know the risk factors involved and what you can do to prevent birth defects.

What are birth defects?

Birth defects are defined as abnormalities of structure, function, or body metabolism that are present at birth. These abnormalities lead to mental or physical disabilities or are fatal. There are more than 4,000 different known birth defects ranging from minor to serious, and although many of them can be treated or cured, they are the leading cause of death in the first year of life.

According to the March of Dimes, about 150,000 babies are born with birth defects each year in the United States. The American College of Obstetricians and Gynecologists (ACOG) says that out of every 100 babies born in the United States, three have some kind of major birth defect.

Birth defects can be caused by genetic, environmental, or unknown factors.

Structural or metabolic birth defects

Structural or metabolic birth defects are those that result when a specific body part is missing or formed incorrectly or when there is an inborn problem in body chemistry. The most common type of major structural defects are heart defects, which affect one in 100 babies in the United States. Some other common structural defects include spina bifida and hypospadias, a condition in which the opening of the male urethra (where urine exits from the penis) is in the wrong place. Metabolic defects affect one in 3,500 babies and usually involve a missing or incorrectly formed enzyme (one of the proteins necessary for processing chemical substances in the body). This type of defect can be harmful or even fatal, but doesn't usually cause any visible abnormalities in the child. Metabolic defects include Tay-Sachs disease, a fatal disease that affects the central nervous system, and phenylketonuria (PKU), which affects the way the body processes protein. Both of these defects will be discussed in more detail later in this article.

Birth defects caused by congenital infections

Birth defects caused by congenital infections result when a mother gets an infection before or during the pregnancy. Examples of infections that can cause birth defects are rubella (German measles), cytomegalovirus (CMV), syphilis, toxoplasmosis, Venezuelan equine encephalitis, parvovirus, and, rarely, chicken pox. None of these infections affect 100% of babies whose mothers are infected during pregnancy. If the mother is infected during early pregnancy, rubella carries the highest risk for birth defects - approximately 20%.

Other causes of birth defects include alcohol abuse by the mother and Rh disease, which can occur when the mother's and baby's Rh factors (the "positive" or "negative" part of a person's blood type) are different. Although a few medications can cause problems, of the 200 most commonly prescribed drugs, none is associated with a significant risk of birth defects.

Common sense precautions to take during pregnancy

Many birth defects can't be prevented; however, there are some common-sense precautions you can take before and during pregnancy.

Before you get pregnant.

Women who are planning to become pregnant should make sure their vaccinations are up to date, that they don't have any sexually transmitted diseases, and that they are getting the daily recommended dose of folic acid (which is present in orange juice and green leafy vegetables, or can be taken as a supplement in pill form).

One way to ensure that you are getting enough is to start taking prenatal vitamins as soon as you begin trying to conceive. It's generally best to avoid unnecessary medications during pregnancy, so make sure you talk to your doctor about any and all over-the-counter and prescription medicines you're taking before you get pregnant; you'll want to stop taking any that aren't vital to your health. Don't do this without talking to your doctor, however.

If you or your partner have a history of any kind of birth defects in your family, if you've already had a child with a birth defect, or if you are part of a high-risk group (because of your age, ethnic background, or medical history), you might want to consult a genetic counselor before you get pregnant. More is being learned about the genes and other factors involved in birth defects all the time and genetic testing and gene therapy are becoming increasingly viable aspects of prepregnancy planning and pregnancy. A genetic counselor can give you advice about prenatal testing and help you deal with any concerns or fears you might have.

While you're pregnant.

The best thing that pregnant women can do to increase their likelihood of having a healthy baby is to make sure they take care of their bodies during pregnancy by:

• not smoking, and avoiding secondhand smoke
• avoiding alcohol
• avoiding all illicit drugs
• eating a healthy diet and taking prenatal vitamins (make sure you're getting enough folic acid)
• getting exercise and plenty of rest
• getting early and regular prenatal care

Talk to your health care provider about other precautions you can take to protect the health of your baby - don't be afraid to ask questions if you're concerned about the possibility of birth defects.