When there is a problem with a baby's body chemistry, it is called a metabolic
birth defect. Metabolic defects prevent the body from properly breaking down
food to create energy. Examples of 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.
For people who want to become parents, it's important to know that some birth defects
can be prevented. During a woman's pregnancy, taking folic
acid and getting enough iodine in the diet
can help prevent some types of birth defects. But it's also important to realize that
most babies born with birth defects are born to two healthy parents with no obvious
health problems or risk factors.
What Causes Birth Defects?
In most cases, doctors don't know what caused a baby's birth defect. When the cause
is known, it might be environmental (such as a baby's exposure to chemicals or viruses
while in the womb), a problem with genes, or a combination of these things.
If a mother has certain infections (such as toxoplasmosis)
during pregnancy, her baby can have a birth defect. Other conditions that cause defects
include rubella and chickenpox
(varicella). Fortunately, many people get vaccinated against these diseases so these
infections are rare.
Also, alcohol abuse by the mother may cause fetal
alcohol syndrome, and certain medicines taken by the mother can cause birth defects.
(Doctors try to avoid harmful medicines during pregnancy, so a pregnant woman should
tell any doctor she consults that she's expecting.)
Every cell in the body has chromosomes containing genes that determine a person's
unique characteristics. During conception, a child inherits one of each pair of chromosomes
(and one of each pair of the genes they contain) from each parent. An error during
this process can cause a baby to be born with too few or too many chromosomes, or
with a damaged chromosome.
One well-known birth defect caused by a chromosome problem is Down
syndrome. A baby develops Down syndrome after getting one extra chromosome. Other
genetic defects happen when both parents pass along a faulty gene for the same disease.
A disease or defect also can happen when only one parent passes along the gene
for that disease. This includes birth defects such as achondroplasia (a form of dwarfism) and Marfan
Finally, some boys inherit disorders from genes passed onto them only by their
mothers. These defects, which include conditions like hemophilia
and color blindness, are called X-linked because the genes are carried on the X chromosome.
How Are Birth Defects Diagnosed?
Many birth defects are diagnosed even before a baby is born through prenatal
tests. Prenatal tests also can help determine if a mother has an infection or
other condition that is dangerous for the fetus. Knowing about a baby's health problems
ahead of time can help parents and doctors plan for the future.
It's important to remember that screening identifies only the possibility that
a baby has a defect. Some women give birth to a healthy baby after a screening test
shows that a defect may be present. If you're pregnant, talk to your doctor about
any tests he or she thinks you should have.
Other birth defects are found during routine newborn
screenings. With parents' permission, babies are tested after birth to screen
for certain birth defects that need to be treated. In the U.S., exactly what a baby
is tested for varies from state to state, although all states screen for phenylketonuria
(PKU), congenital hypothyroidism,
sickle cell disease, and
about 30 other conditions. Parents should ask health care providers or the hospital
nursery which tests their state does.
Parents who have concerns about another specific birth defect might be able to
have their baby tested for it. They should talk to their health care provider about
it before the baby is born.
Can Birth Defects Be Prevented?
Many birth defects can't be prevented, but a woman can do some things before and
during pregnancy to help lower the chances of having a baby with a birth defect.