Overview of Birth Defects
What is a birth defect?
A "birth defect" is a health problem or physical change, which is present in a baby
at the time he or she is born. Birth defects may be very mild, where the baby looks
and acts like any other baby, or birth defects may be very severe, where you can immediately
tell there is a health problem present. Some of the severe birth defects can be life-threatening,
where a baby may only live a few months, or may die at a young age (in their teens,
Birth defects are also called "congenital anomalies" or "congenital abnormalities."
The word "congenital" means "present at birth." The words "anomalies" and "abnormalities"
mean that there is a problem present in a baby.
What causes birth defects to occur?
There are many reasons why birth defects happen. Most occur due to environmental and
genetic factors, but often the cause is unknown.
Who is affected by birth defects?
Birth defects have been present in babies from all over the world, in families of
all nationalities 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 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 cannot be answered. This can be
very upsetting for parents because it is normal to seek an answer as to why your baby
has a health problem. For some birth defects, however, there is a known cause, which
may have to do with either genetic or environmental factors, or a combination of the
two. Here is some general information and terms related to the different causes of
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
Chromosome abnormalities. Chromosomes are stick-like structures in the center of each cell (called the nucleus)
that contain your genes.
Single gene defects. Genes are what determine your traits. Sometimes, a child can inherit not only those
genes responsible for their normal traits such as the color of their eyes, but also
disease causing genes that result in a birth defect.
Multifactorial inheritance. Multifactorial inheritance means that "many factors" (multifactorial) are involved
in causing a birth defect. The factors are usually both genetic and environmental.
Teratogens. A teratogen is an agent, which 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 medication, a street drug, alcohol use, or a disease that the mother
has, which could increase the chance for the baby to be born with a birth defect.
Why are birth defects a concern?
Although some birth defects have a single abnormality, others have abnormalities in
multiple body systems or organs. Birth defects may cause lifelong disability and illness,
and with some, survival is not possible.
Some birth defects, such as intellectual disability, are nontreatable disabilities.
However, many physical birth defects can be treated with surgery. Repair is possible for
many birth defects including cleft lip or palate, and certain heart defects.
How are birth defects diagnosed?
Many birth defects can be diagnosed before birth with special tests (prenatal diagnosis).
Chromosomal abnormalities such as Down syndrome can be diagnosed before birth by analyzing
cells in the amniotic fluid or from the placenta. Fetal ultrasound during pregnancy
can also give information about the possibility of certain birth defects, but ultrasound
is not 100 percent accurate, since some babies with birth defects may look the same
on ultrasound as those without problems. A chromosome analysis, whether performed
on a blood sample or cells from the amniotic fluid or placenta, is very accurate.
Tests that help screen for birth defects include the following:
Alpha-fetoprotein. This blood test measures the levels of alpha-fetoprotein (AFP), a protein released
by the fetal liver and found in the mother's blood. AFP is sometimes called MSAFP
(maternal serum AFP). AFP screening may be included as one part of a two, three, or
four-part screening, often called a multiple marker screen. The other parts may include
HCG. Human chorionic gonadotropin (hCG) is a hormone secreted by the early placental cells.
High hCG levels may indicate a fetus with Down syndrome (a chromosomal abnormality
that includes intellectual disability and distinct physical features).
Estriol. A hormone produced by the placenta and by the fetal liver and adrenal glands. Low
levels may indicate a fetus with Down syndrome.
Inhibin. A hormone produced by the placenta.
Nuchal translucency screening. An ultrasound test usually performed in the late first trimester. Thickening of the
area at the back of the fetal neck may indicate an increased risk for Down syndrome
or other chromosomal problems.
Chorionic villus sampling (CVS). A prenatal test that involves taking a sample of some of the placental tissue. This
tissue contains the same genetic material as the fetus and can be tested for chromosomal
abnormalities and some other genetic problems. Testing is available for other genetic
defects and disorders depending on the family history and availability of laboratory
testing at the time of the procedure. In comparison to amniocentesis (another type
of prenatal test), CVS does not provide information on neural tube defects, such as
spina bifida. For this reason, women who undergo CVS also need a follow-up blood test
between 16 to 18 weeks of their pregnancy, to screen for neural tube defects.
Amniocentesis. A procedure used to obtain a small sample of the amniotic fluid that surrounds the
fetus to diagnose chromosomal disorders and open neural tube defects (ONTDs), such
as spina bifida. Testing is available for other genetic defects and disorders depending
on the family history and availability of laboratory testing at the time of the procedure.
The American College of Obstetricians and Gynecologists recommends amniocentesis around
15 weeks to 20 weeks of pregnancy for those women who are at increased risk for chromosome
abnormalities, such as women who are over age 35 years of age at delivery, or those
who have had an abnormal maternal serum screening test, indicating an increased risk
for a chromosomal abnormality or neural tube defect. However, in some situations,
amniocentesis may be performed as early as 14 weeks.
Ultrasound. A diagnostic technique that uses high-frequency sound waves to create an image of
the internal organs. Many birth defects can be detected with ultrasound.
Sometimes, birth defects are not diagnosed until physical examination of the baby
after birth. To confirm the physical findings, a small blood sample can be taken and
the chromosomes can be analyzed. This information is important in determining the
risk for that birth defect in future pregnancies.
Prevention of birth defects
Research is ongoing to find and treat the causes of many birth defects. Immunizations
of the mother against certain infections, such as rubella, can prevent birth defects
caused by that infection. Much has been learned about the dangerous effects of alcohol
on the developing baby and women are advised to not drink alcohol during pregnancy.
In recent years, a strong link has been discovered between the lack of the B-vitamin
folic acid and the development of neural tube defects, such as spina bifida. Taking
a vitamin containing sufficient folic acid before conception and in early pregnancy
can often help prevent many serious birth defects.