Birth defects are physical abnormalities that are present at birth. They arealso called congenital abnormalities. More than 3,000 have been identified.
Birth defects are found in 2-3% of all newborn infants. This rate reaches 10%by age five, as more defects become evident. Almost 20% of deaths in newborns are caused by birth defects.
Abnormalities can occur in any organ or part of the body. Major defects are structural abnormalities that require medical and/or surgical treatment. Minordefects are abnormalities that do not cause serious health or social problems.
The specific cause of many congenital abnormalities is unknown. Any substancethat can causes abnormal development of the egg in the mother's womb is called a teratogen. Growth in the uterus is rapid, and each body organ has a critical period in which it is especially sensitive to outside influences. About7% of all congenital defects are caused by exposure to teratogens.
Only a few drugs are known to cause birth defects, but all drugs have the potential to cause harm. Thalidomide causes defects of the arms and legs. Drinking large amounts of alcohol while pregnant causes a cluster of defects calledfetal alcohol syndrome that include mental retardation, heart problems, andgrowth deficiency. Tetracycline, an antibiotic, affects bone growth and discolors the teeth.
Drugs used to treat, sulfa drugs, and some drugs given to treat anxiety and mental illness are known to cause specific defects. Drugs given to treat cancer can cause major central nervous system defects. Male hormones may cause masculinization of a female fetus.
Recreational drugs such as LSD have been associated with arm and leg abnormalities and central nervous system problems in infants, as has crack cocaine. Since drug abusers tend to use many drugs and have poor nutrition and prenatalcare, it is hard to determine the effects of individual drugs.
Environmental chemicals such as fungicides, food additives, and pollutants are suspected of causing birth defects, although this is difficult to prove. Exposure of the mother to high levels of radiation can cause small skull size (microcephaly), blindness, spina bifida (a malformation of the spinal cord), and cleft palate. How severe the defect is depends on the duration and timingof the exposure.
Three viruses are known to harm a developing baby are rubella (German measles), cytomegalovirus (CMV), and herpes simplex. Toxoplasma gondii, a parasite that can be contracted from undercooked meat, dirt, or handling the feces of infected cats, causes serious problems. Untreated syphilis in the mother is also harmful.
In addition to outside influences, some people carry genes for specific birthdefects. A gene is a small unit containing information (DNA) that guides howthe body forms and functions. Each person inherits many genes from each parent, arranged on 46 chromosomes. Genes control all aspects of the body, how itworks, and all its unique characteristics. Genes can be damaged by chemicalsand radiation, but sometimes changes in the genes are unexplained accidents.
Birth defects caused by defective genes include a form of dwarfism called achondroplasia; Huntington's disease, a progressive nervous system disorder; Marfan syndrome, which affects connective tissue; some forms of glaucoma; and the development of extra fingers or toes.
Other inherited birth defects include sickle-cell anemia, a blood disorder found mainly in African-Americans that affects the amount of oxygen the blood can carry and Tay-Sachs disease, which causes mental retardation and early death, and is found mainly in people of eastern European Jewish heritage. Two genetic disorders that affect mostly Caucasians are cystic fibrosis, a lung anddigestive disorder, and phenylketonuria (PKU), a metabolic disorder.
Other common genetic birth defects include hemophilia, a condition that prevents blood from clotting, Duchenne muscular dystrophy, which causes muscle weakness, and Down syndrome.
Birth defects whose causes are less understood include cleft lip and palate,clubfoot, spina bifida, water on the brain (hydrocephalus), diabetes mellitus, and some heart defects.
There is no way to prevent all birth defects. If there is a family history ofbirth defects or if the mother is over age 35, screening tests can be done during early pregnancy to gain information about the likelihood of a birth defect being present. Based on this information, some parents may choose to terminate the pregnancy.
If a birth defect is suspected after a baby is born, confirmation of the diagnosis is necessary. Treatment depends on the type of birth defect and how serious it is. Some abnormalities can be corrected with surgery. Experimental procedures have been used successfully in correcting other defects. Researchershope that classify term="Gene therapy" type="print-hyplink">gene therapy will eventually correct many birth defects.
The risk of birth defects can be reduced by limiting exposure to chemicals, radiation, alcohol, and drugs (recreational and medicinal) before and during pregnancy. When there is a family history of congenital defects in either parent, genetic counseling and testing can help parents plan for future children.