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birth defects,abnormalities in physical or mental structure or function that are present at birth. They range from minor to seriously deforming or life-threatening. A major defect of some type occurs in approximately 3% of all births. Defects may be genetic in origin, as in Down syndromeDown syndrome,
congenital disorder characterized by mild to severe mental retardation, slow physical development, and characteristic physical features. Down syndrome affects about 1 in every 730 live births and occurs in all populations equally.
..... Click the link for more information. , Tay-Sachs diseaseTay-Sachs disease
, rare hereditary disease caused by a genetic mutation that leaves the body unable to produce an enzyme necessary for fat metabolism in nerve cells, producing central nervous system degeneration.
..... Click the link for more information. , sickle cell diseasesickle cell disease
or sickle cell anemia,
inherited disorder of the blood in which the oxygen-carrying hemoglobin pigment in erythrocytes (red blood cells) is abnormal.
..... Click the link for more information. , and hemophiliahemophilia
, genetic disease in which the clotting ability of the blood is impaired and excessive bleeding results. The disease is transmitted through females but almost invariably affects male offspring only.
..... Click the link for more information. , or may be the result of infections, such as rubellarubella
or German measles,
acute infectious disease of children and young adults. It is caused by a filterable virus that is spread by droplet spray from the respiratory tract of an infected individual.
..... Click the link for more information. and sexually transmitted diseasessexually transmitted disease
(STD) or venereal disease,
term for infections acquired mainly through sexual contact. Five diseases were traditionally known as venereal diseases: gonorrhea, syphilis, and the less common granuloma inguinale, lymphogranuloma venereum, and
..... Click the link for more information. . Other teratogenic (malformation-causing) agents include drugs or hormones taken by the mother (e.g., thalidomidethalidomide
, sleep-inducing drug found to produce skeletal defects in developing fetuses. The drug was marketed in Europe, especially in West Germany and Britain, from 1957 to 1961, and was thought to be so safe that it was sold without prescription.
..... Click the link for more information. and DESDES
, synthetic nonsteroid female sex hormone having the same physiological effects as estrogen. In the 1940s and 50s DES was mistakenly believed to reduce the risk of miscarriage and was routinely prescribed for pregnant women believed to be at
..... Click the link for more information. ) and maternal illnesses (e.g., diabetesdiabetes
or diabetes mellitus
, chronic disorder of glucose (sugar) metabolism caused by inadequate production or use of insulin, a hormone produced in specialized cells (beta cells in the islets of Langerhans) in the pancreas that allows the body to use and store
..... Click the link for more information. ). The mother's nutrition, drinking (see fetal alcohol syndromefetal alcohol syndrome
(FAS), pattern of physical, developmental, and psychological abnormalities seen in babies born to mothers who consumed alcohol during pregnancy. The abnormalities include low birthweight, facial deformities, and mental retardation, and there appears to be
..... Click the link for more information. ), smokingsmoking,
inhalation and exhalation of the fumes of burning tobacco in cigars and cigarettes and pipes. Some persons draw the smoke into their lungs; others do not. Smoking was probably first practiced by the indigenous peoples of the Western Hemisphere.
..... Click the link for more information. , and drug abuse, as well as exposure to toxic chemicals and radiation, can also affect the developing fetus. Smoking, drugs, toxic chemicals, and the like can also damage the father's sperm, which may pass on the defect to the embryo in fertilization. The incidence of some disorders is elevated when the mother or father is older, which increases the likelihood of age-related gene mutations. Certain birth defects can now be detected prenatally through amniocentesisamniocentesis
, diagnostic procedure in which a sample of the amniotic fluid surrounding a fetus is removed from the uterus by means of a fine needle inserted through the abdomen of the pregnant woman (see pregnancy).
..... Click the link for more information. and chorionic villus samplingchorionic villus sampling
(CVS) or chorionic villus biopsy
(CVB) , diagnostic procedure in which a sample of chorionic villi from the developing placenta is removed from the uterus of a pregnant woman (see pregnancy) using a fine needle inserted through the abdomen or
..... Click the link for more information. . Surgical procedures to correct certain disorders before birth are still considered experimental.