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BIRTH DEFECTS ALL pregnancies are at
risk
for birth defects,
regardless of the patient's age, health status, previous history, family
history, or life style. Birth defects are not uncommon, affecting at
least 2% of pregnancies. Fortunately, most birth defects are minor
while major birth defects are much less common. However, a number of
serious birth defects occur in the range of 1 in 1000 pregnancies. Screening
tests are
available that can detect the vast majority of these serious birth
defects. For parents of affected infants, a number of parent
support
groups are available. In addition to
categorizing birth defects as minor or major, they can also be
categorized into two broad groups: BIRTH DEFECTS WITH NORMAL CHROMOSOMES Most birth defects are sporadic types of birth defects that can involve any organ system: the brain, spine, face, heart, kidneys, extremities, lungs, gastrointestinal tract, etc. These may be either major or minor. In most cases, the cause of the defect cannot be identified but simply reflects the complexity in making humans. Sometimes multiple anomalies may be present and fit the description of a "syndrome". A syndrome is a recognized pattern of birth defects. Fortunately, a detailed fetal scan, when performed by skilled personnel, can detect the vast majority of major birth defects. For example, high quality ultrasound can detect nearly all open spinal defects so that a normal screening ultrasound virtually eliminates the possibility of a significant spinal defect. Major anomalies involving other organ systems can also generally be identified. However, minor defects may remain undetected, however. There are also cetain types of anomalies that develop later in pregnancy and so cannot be detected early. A number of other types of birth defects may not be detected by either routine ultrasound or routine genetic amniocentesis, but can be detected or suspected if special tests are performed. If the condition is common in the general population, all women may be offered the screening test-for example cystic fibrosis. Other types of tests may be offered only to women in certain ethnic groups- for example, Ashkenazim Jews (ones of Eastern European descent) are at increased risk of Tay-Sachs disease, Canavan disease, as well as certain other conditions. Screening for other syndromes or genetic conditions may be offered only if there is a personal or family history of that particular condition. For many other conditions or genetic diseases, prenatal testing may not yet be available. BIRTH DEFECTS WITH CHROMOSOME ABNORMALITIES
Another important
category of birth defects are those caused by
chromosome abnormalities.
In these cases, we know what causes the birth defects since chromosomes
are the "blue prints" or "DNA" who make us what we are. Although the
birth defects themselves may be corrected or improved after birth, the
underlying chromosome abnormality is always present. Humans have 23
pairs of chromosomes, or 46 total. Some of the major chromosome
abnormalities affect the number of chromosomes so there may be too many
(the usual case) or too few. Trisomy 21 (Down
syndrome) is
one of the most common of the major chromosome abnormalities that may be
seen at birth -there are more serious chromosome abnormalities but these
may not survive to birth or beyond. In the case of Down syndrome,
affected individuals have 3 copies of the 21st chromosome or 47
altogether. Because chromosomes are in nearly every cell of the body,
they can affect any organ system. Affected individuals also tend to be
mentally delayed. Down syndrome affects approximately 1 in 500
pregnancies in the U.S.
TRISOMY 21 |
