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Birth Defects
About 120,000 babies (1 in 33) in the United States are born each year with birth defects
(1). A birth defect is an abnormality of structure, function or metabolism (body
chemistry) present at birth that results in physical or mental disabilities or death. Several
thousand different birth defects have been identified. Birth defects are the leading cause
of death in the first year of life (2).
What causes birth defects?
Both genetic and environmental factors, or a combination of these factors, can cause birth
defects. However, the causes of about 70 percent of birth defects are unknown (1). Birth
defects in the U.S. have generally been increasing since World War II, though the
Centers for Disease Control has not kept records since 1967, with some notable
exceptions. The first exception in the US was due to the addition of folic acid to the
grain supply, afterwards, the incidence of neural tube (brain and spinal chord) defects
have decreased by 1/3 per year (similar results for other first world countries). Secondly,
after the availability of the vaccine for the German measles in 1969, there was a short
lived decrease in the number of birth defects. As the German measles was the leading
cause of birth defects before 1969, the drop in birth defects was anticipated. It has never
been understood or explained why the drop was of a short duration and subsequently
disappeared. Without the leading cause of birth defects before 1969, the German
measles, researchers are puzzled by why the rates are so high.
Causes and Risks
It is not surprising that birth defects are fairly common, considering the complexities involved in the
development of a single fertilized egg into the millions of specialized cells that constitute a human being.
Although the cause of most birth defects is unknown, certain genetic and environmental factors increase the
chance of birth defects developing. These factors include exposure to radiation, certain drugs (see Some
Drugs That Can Cause Problems During Pregnancy*), alcohol, isotretinoin, ACCUTANE , nutritional
deficiencies, certain infections in the mother, injuries, and hereditary disorders. Some risks are avoidable.
Others occur no matter how strictly a pregnant woman adheres to healthful living practices.
Exposure to Harmful Substances (Teratogens): A teratogen is any substance that can cause or increase
the chance of a birth defect. Radiation (including x-rays), certain drugs, and toxins (including alcohol) are
teratogens. Most pregnant women who are exposed to teratogens have newborns without abnormalities.
Whether or not a birth defect occurs depends on when, how much, and how long the pregnant woman was
exposed to the teratogen. Exposure to a teratogen most commonly affects the fetal organ that is developing
most rapidly at the time of exposure. For example, exposure to a teratogen during the time that certain parts
of the brain are developing is more likely to cause a defect in those areas than exposure before or after this
critical period. Many birth defects develop before a woman knows she is pregnant.
Nutrition: Keeping a fetus healthy requires maintaining a nutritious diet. For example, insufficient folic acid
(folate) in the diet increases the chance that a fetus will develop spina bifida or other abnormalities of the
brain or spinal cord known as neural tube defects (see Genetic Disorders Detection: Neural Tube Defects).
Cleft lip or cleft palate is also more likely to develop. Maternal obesity also increases the risk of a neural tube
defect.
Single gene defects:
In some cases, a single gene change can cause birth defects.
Every human being has about 20,000 to 25,000 genes that determine traits like eye and
hair color (3). Genes also direct the growth and development of every part of our physical
and biochemical systems. Genes are packaged into each of the 46 chromosomes inside
our cells.
Each child gets half its genes from each parent. A person can inherit a genetic disease
when one parent (who may or may not have the disease) passes along a single faulty
gene. This is called “dominant inheritance.” Examples include:
Achondroplasia (a form of dwarfism)
Marfan syndrome (a connective tissue disease)
Many other genetic diseases are inherited when both parents (who do not have the
disease) carry an abnormality in the same gene and pass it on to a child. This is called
“recessive inheritance.” Examples include:
Tay-Sachs disease (a fatal nervous system disorder)
Cystic fibrosis (a serious disorder of lungs and other organs, affecting mainly Caucasians)
There also is a form of inheritance called “X-linked,” in which sons can inherit a genetic
disease from a mother who carries the gene (usually with no effect on her own health).
Examples include:
Hemophilia (a blood-clotting disorder)
Chromosomal birth defects: Abnormalities in the number or structure of
chromosomes can cause many birth defects. Chromosomal abnormalities usually
result from an error that occurred when an egg or sperm cell was developing. As a
result of this error, a baby can be born with too many or too few chromosomes, or
with one or more chromosomes that are broken or rearranged.
Environmental factors: Environmental substances that can cause birth defects are
called teratogens. These include alcohol, certain drugs/medications, infections, and
certain chemicals.
Each year between 1,000 and 6,000 babies are born with fetal alcohol syndrome
(FAS) in this country (4). FAS is a pattern of mental and physical birth defects that is
common in babies of mothers who drink heavily during pregnancy. Women who are
pregnant or planning pregnancy should not drink any alcohol. Even moderate or light
drinking during pregnancy may harm the baby.
Some drugs and medications can contribute to birth defects. For example, the acne
drug isotretinoin (sold under the brand names Accutane, Amnesteem, Claravis and
Sotret) poses a high risk of serious birth defects. A woman who is pregnant or who
could become pregnant should never use this drug. Illicit drugs such as cocaine also
may pose a risk.
Certain infections can result in birth defects when a woman contracts them during
pregnancy. About 40,000 babies a year (about 1 percent of all newborns in this
country) are born with a viral infection called cytomegalovirus (CMV) (5). About 1 in
10 infected babies develop serious disabilities, including mental retardation and loss
of vision and hearing (5). Pregnant women often get CMV from young children who
have few or no symptoms.
Sexually transmitted infections in the mother also can endanger the fetus and
newborn. For example, untreated syphilis can result in stillbirth, newborn death or
bone defects. About 412 babies were affected by congenital syphilis in 2002(6).
Multi-factorial birth defects: Some birth defects appear to be caused by a
combination of one or more genes and environmental exposures. This is called
“multi-factorial inheritance.” In some cases, an individual may inherit one or more
genes that make him more likely to have a birth defect if he is exposed to certain
environmental substances (such as cigarette smoke). These individuals have a
genetic predisposition to a birth defect. But if the individual is not exposed to the
environmental substance before birth, he probably won’t have the birth defect.
Examples of multi-factorial birth defects include:

Cleft lip/palate (opening in the lip and/or roof of the mouth)

Neural tube defects (serious birth defects of the brain and spinal cord,
including spina bifida and anencephaly)

Heart defects
What are the most common birth defects?
Cleft lip/palate and Down syndrome are among the most common birth defects in
the United States (7). About 6,800 babies are born with cleft lip/palate each year.
Foreign Correspondent, ABC, 9.20pm
On the 19th anniversary of the Chernobyl nuclear disaster, Foreign Correspondent
broadcasts Chernobyl Heart, an Academy Award-winning documentary. It takes us into
the cities and towns around the site of the doomed Ukrainian power station, concentrating
on the mammoth increase in birth defects and thyroid cancers since the power station
blew up.
We are taken to an area near the reactor where, even now, the Geiger counter reads
11,000. Major cities usually have a background reading of around 12 - but that is not the
most distressing fact.
An orphanage in Minsk is home to abandoned children with the most horrifying birth and
congenital defects: a four-year-old with her brain growing outside her head; a little boy
with distended kidneys the size of rockmelons; and a living skeleton whose body ends at
the waist.
In comes Dr William Novick, a US surgeon who visits the Ukraine regularly to perform
life-saving operations on children with "Chernobyl heart", a common defect in this region
that results in holes in the heart. Novick and his aides sew Gortex into the walls of the
heart, giving some of the luckier children a chance of survival.
Folic Acid
In the US, after the addition of folic acid to the grain supply, the incidence of neural tube
(brain and spinal chord) defects have decreased by 1/3 per year.