Birth defects

A birth defect is an abnormal condition that is present at birth, regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can range from mild to severe. Birth defects are divided into two main types: structural disorders in which problems are seen with the shape of a body part and functional disorders in which problems exist with how a body part works. Functional disorders include metabolic and degenerative disorders. Some birth defects include both structural and functional disorders.

Birth defects may result from genetic or chromosomal disorders, exposure to certain medications or chemicals, or certain infections during pregnancy. Risk factors include folate deficiency, drinking alcohol or smoking during pregnancy, poorly controlled diabetes, and a mother over the age of 35 years old. Many birth defects are believed to involve multiple factors. Birth defects may be visible at birth or diagnosed by screening tests. A number of defects can be detected before birth by different prenatal tests.

Treatment varies depending on the defect in question. This may include therapy, medication, surgery, or assistive technology. Birth defects affected about 96 million people . In the United States, they occur in about 3% of newborns. They resulted in about 628,000 deaths in 2015, down from 751,000 in 1990. The types with the greatest numbers of deaths are congenital heart disease (303,000), followed by neural tube defects (65,000).

Classification

Much of the language used for describing congenital conditions antedates genome mapping, and structural conditions are often considered separately from other congenital conditions. Many metabolic conditions are now known to have subtle structural expression, and structural conditions often have genetic links. Still, congenital conditions are often classified on a structural basis, organized when possible by primary organ system affected.

Primarily structural

Several terms are used to describe congenital abnormalities. (Some of these are also used to describe noncongenital conditions, and more than one term may apply in an individual condition.)

Terminology

* A congenital physical anomaly is an abnormality of the structure of a body part. It may or may not be perceived as a problem condition. Many, if not most, people have one or more minor physical anomalies if examined carefully. Examples of minor anomalies can include curvature of the fifth finger ( clinodactyly), a third nipple, tiny indentations of the skin near the ears ( preauricular pits), shortness of the fourth metacarpal or metatarsal bones, or dimples over the lower spine ( sacral dimples). Some minor anomalies may be clues to more significant internal abnormalities.
* Birth defect is a widely used term for a congenital malformation, ''i.e.'' a congenital, physical anomaly that is recognizable at birth, and which is significant enough to be considered a problem. According to the Centers for Disease Control and Prevention (CDC), most birth defects are believed to be caused by a complex mix of factors including genetics, environment, and behaviors,Birth Defects Research
. Centers for Disease Control and Prevention. though many birth defects have no known cause. An example of a birth defect is cleft palate, which occurs during the fourth through seventh weeks of gestation. Body tissue and special cells from each side of the head grow toward the center of the face. They join to make the face. A cleft means a split or separation; the "roof" of the mouth is called the palate.
* A congenital malformation is a physical anomaly that is deleterious, ''i.e.'' a structural defect perceived as a problem. A typical combination of malformations affecting more than one body part is referred to as a malformation syndrome.
* Some conditions are due to abnormal tissue development:
** A malformation is associated with a disorder of tissue development. Malformations often occur in the first trimester.
** A dysplasia is a disorder at the organ level that is due to problems with tissue development.
* Conditions also can arise after tissue is formed:
** A deformation is a condition arising from mechanical stress to normal tissue. Deformations often occur in the second or third trimester, and can be due to oligohydramnios.
** A disruption involves breakdown of normal tissues.
* When multiple effects occur in a specified order, they are known as a sequence. When the order is not known, it is a syndrome.

Examples of primarily structural congenital disorders

A limb anomaly is called a dysmelia. These include all forms of limbs anomalies, such as amelia, ectrodactyly, phocomelia, polymelia, polydactyly, syndactyly, polysyndactyly, oligodactyly, brachydactyly, achondroplasia, congenital aplasia or hypoplasia