health

Birth defects are abnormalities in the body structure or chemistry that
occur while the fetus* is developing in the mother’s uterus. Hereditary or
genetic causes, environmental influences, or a combination of factors may
affect the embryo or fetus before it is born. Sometimes, the cause of a birth
defect is unknown.

In 1994 and 1995, a number of infants along the Rio Grande in Texas
and Mexico were born without a brain, a condition called anencephaly
(an-en-SEF-a-lee). Some professionals suspected that the birth defects
occurred when mothers were exposed to pollution in the environment.
Although in the early 2000s there continued to be many unknowns about
causes of birth defects, scientists knew that the human embryo is exceedingly
vulnerable to drugs, viruses, and radiation during the first several
months when critical systems are forming.
Some birth defects are inherited from parents, and others are acquired
through the mother’s contact with the environment or with disease.
According to the March of Dimes, 3 to 5 percent of babies born in the
United States have some type of birth defect. Some birth defects, such as
anencephaly*, occur infrequently. Others, such as some congenital* heart
defects, are more common. Some hereditary defects are more common in
certain populations than in others.