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Birth defects range from minimal, such as birthmarks, and slightly mobility-impairing, such as amelia of the legs, to very serious, such as cerebral palsy, and incompatible with life, such as anencephaly.

The majority of malformations are from unknown or multifactorial causes. About 20% of birth defects result from genetic abnormalities, and another 5% because of chromosomal problems. Others can arise from chance problems in fetal development ( teratogenesis), which are sometimes caused by prenatal vitamin deficiencies or exposure to mercury and other harmful substances. Infection and disease in the mother can also cause birth defects.

About 2-3% of babies are born with congenital defects. The incidence is highest in the brain (10 per 1000 live births), heart (8 per 1000), kidneys (4 per 1000) and limbs (2 per 1000). All other defects have an combined incidence of 6 per 1000 live births.

Risk of birth defects throughout gestation

The greatest risk of a malformation occurring is between the third and eighth week of gestation. Before this time, any damage to the embryo is likely to result in fatality and the baby will not be born. After eight weeks, the fetus and its organs are more developed, and is less sensitive to teratogenic incidents.

The type of birth defect is also related to the time of exposure to a teratogen. For instance the heart is susceptible from three to eight weeks, but the earFor an alternative meaning, see ear (botany). human ear. An ear is an organ used by an animal to detect sound. The term may refer to the entire system responsible for collection and early processing of sound (the beginning of the auditory system), or mere is susceptible from a slightly later time to about twelve weeks.

Infection in the mother early in the third week may damage the heart. An infection in the eleventh week is less likely to damage the heart, but the baby may be born deafTo be deaf is commonly understood to mean to be unable to hear, or to affiliate oneself with Deaf culture. Deaf versus deaf Main article: Deaf culture The word deaf is used and understood in two ways. First, there is the medical, pathological and audiolog.

Some other birth defects:

• cleft lipCleft lip is a congenital deformity caused by a failure in facial development during pregnancy. It can be treated with surgery early upon birth with highly successful results. Cleft lip occurs in somewhere between one in 600 and one in 800 births. It is c
• cleft palateCleft palate is a condition in which the two plates of the skull that form the hard palate (roof of the mouth) are not completely joined. In some cases, cleft lip is present as well. Complications Cleft palate may cause problems with feeding, ear disease,
• club footA club foot or talipes is a birth defect. The foot is twisted in such a way that it cannot be completely corrected without the aid of surgery. Persons afflicted often appear to walk on their ankles, or on the sides of their feet. It is the most common bir
• spina bifidaSpina bifida describes birth defects caused by an incomplete closure of one or more vertebral arches of the spine, resulting in malformations of the spinal cord. The spinal membranes and spinal cord may protrude through the absence of vertebral arches (ca