Overview of Birth Defects
What is a birth defect?
A birth defect is a health problem or physical change that is present when a baby
is born. Birth defects can be very mild, where the baby looks and acts like any other
baby. Or birth defects can be very serious. You can tell right away that the baby
has a health problem. Some of the severe birth defects can be life-threatening. A
baby may only live a few months. Or the child may die at a young age—when he or she
is a teen, for example.
Birth defects are also called congenital anomalies or congenital abnormalities. The
word congenital means present at birth. The words anomalies and abnormalities mean
that the baby has a problem.
What causes birth defects?
Birth defects can happen for many reasons. They can happen because of the mother’s
exposure to certain things while she is pregnant. Or they can happen because of certain
genes or changes in genes (mutations). But often the cause isn’t known.
Who is affected by birth defects?
Birth defects are found in babies all over the world, in families of from all countries
and backgrounds. Anytime a couple becomes pregnant, there is a chance that their baby
will have a birth defect. Most babies are born healthy. In fact, 97 out of every 100
babies are born healthy.
What are the genetic and environmental causes of birth defects?
When a baby is born with a birth defect, the first question usually asked by the parents
is "how did this happen?" Sometimes, this question can’t be answered. This can be
very upsetting for parents because it’s normal to want to know why your baby has a
health problem. But for some birth defects, the cause is known. It may have to do
with exposure to certain things during pregnancy. Or it may have to do with genes
or gene changes (mutations). It could also be a combination of these two things.
Here is some general information about the different causes of birth defects:
Inheritance. Inheritance is a word used to describe a trait given to you or passed on to you from
one of your parents. Examples of inherited traits would be your eye color or blood
Chromosome abnormalities. Chromosomes are stick-like structures in the center (nucleus) of each cell that contain
Single gene defects. Genes are what give you your traits. Sometimes a child can inherit not only those
genes for their normal traits such as the color of their eyes, but also disease-causing
genes that cause a birth defect.
Multifactorial inheritance. Multifactorial inheritance means that many things are involved in causing a birth
defect. The factors are usually both genetic and environmental.
Teratogens. A teratogen is a substance that can cause a birth defect. It is usually something
in the environment that the mother may be exposed to during her pregnancy. It could
be a prescribed medicine, a street drug, alcohol use, or a disease that the mother
has. Any of these could increase the chance for the baby to be born with a birth defect.
Why are birth defects a concern?
Some birth defects cause a single problem, but others cause problems in more than
one body system or organ. Birth defects may cause lifelong disability and illness.
Some mean that the baby will not survive.
Some birth defects can’t be treated. These include defects that cause learning or
thinking problems. But many physical birth defects can be treated with surgery. Repair
is possible for many birth defects, including cleft lip or palate, and certain heart
How are birth defects diagnosed?
Many birth defects can be diagnosed before birth with special tests. Chromosome problems
such as Down syndrome can be diagnosed before birth by looking at cells in the amniotic
fluid or from the placenta. Or they can be found by looking at the fetal DNA in the
mother’s blood (noninvasive prenatal screening).
Fetal ultrasound during pregnancy can also show the possibility of certain birth defects.
But ultrasound is not 100% accurate. Some babies with birth defects may look the same
on ultrasound as those without problems. The chromosome analysis done on a blood sample
or on cells from the amniotic fluid or placenta is very accurate.
Tests that help screen for birth defects include:
Alpha-fetoprotein. This blood test measures the levels of alpha-fetoprotein (AFP). This is a protein
released by the developing baby’s liver and found in the mother's blood. AFP is sometimes
called MSAFP (maternal serum AFP). AFP screening may be one part of a 2-, 3-, or 4-part
screening, often called a multiple marker screen. The other parts are:
HCG. Human chorionic gonadotropin (hCG) is a hormone released by the early cells in the
placenta. High hCG levels may mean that the fetus has Down syndrome. This condition
is a chromosome problem includes learning problems and certain facial features.
Estriol. Estriol is a hormone made by the placenta and by the fetal liver and adrenal glands.
Low levels may mean the fetus has Down syndrome.
Inhibin. This is a hormone made by the placenta.
Nuchal translucency screening. This is an ultrasound test usually done late in the first trimester. Thickening of
the area at the back of the fetal neck may mean an increased risk for Down syndrome
or other chromosome problems.
Chorionic villus sampling (CVS). This is a prenatal test that takes a sample of some of the placental tissue. This
tissue has the same genetic material as the fetus. It can be tested for chromosome
problems and some other genetic problems. Testing can be done for other genetic defects
and disorders, depending on family history and lab testing available at the time of
the test. Unlike amniocentesis, CVS does not give information on neural tube defects
such as spina bifida. Women who have the CVS test also need a follow-up blood test
between 16 and 18 weeks of their pregnancy to screen for neural tube defects.
Amniocentesis. This test takes a small sample of the amniotic fluid that surrounds the fetus. The
sample is used to diagnose chromosome problems and open neural tube defects such as
spina bifida. Testing can be done for other genetic defects and disorders, depending
on family history and lab testing available at the time of the test.
The American College of Obstetricians and Gynecologists recommends amniocentesis around
15 to 20 weeks of pregnancy for those women who are at higher risk for chromosome
problems. These include women who are over age 35 at delivery. It also includes women
who have had an abnormal blood test that means they are at higher risk for a chromosome
problem or neural tube defect. In some cases, amniocentesis may be done as early as
Ultrasound. This is a test that uses high-frequency sound waves to create an image of the internal
organs. Many birth defects can be found with ultrasound.
Noninvasive prenatal screening. This is a test that looks at the mother's blood. The lab looks for genetic material
called DNA that comes from the placenta. This DNA is the same as the fetus’ DNA. The
lab looks for chromosome problems such as trisomy 13, trisomy 18, and trisomy 21.
Sometimes, birth defects are not diagnosed until after birth. To confirm the physical
findings, the healthcare provider will take a small blood sample so the chromosomes
can be looked at. This information is important in knowing the risk for that birth
defect in future pregnancies.
Preventing birth defects
Research is ongoing to find and treat the causes of many birth defects. Getting vaccinated
against certain infections such as rubella can prevent birth defects caused by that
infection. Not drinking during pregnancy can prevent birth defects caused by alcohol.
Taking a prenatal vitamin that includes folic acid can help prevent neural tube defects
such as spina bifida.