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Overview of Birth Defects

By

Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision Jul 2019| Content last modified Jul 2019
Click here for the Professional Version
Topic Resources

Birth defects, also called congenital anomalies, are physical abnormalities that occur before a baby is born. They are usually obvious within the first year of life.

Birth defects can involve any part of any organ in the body, including the following:

Some birth defects are more common than others.

A birth defect is evident in about 7.5% of all children by age 5 years, although many of these are minor. Major birth defects are evident in about 3 to 4% of newborns.

Several birth defects can occur together in the same infant.

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Causes of and Risk Factors for Birth Defects

It is not surprising that birth defects are fairly common, considering the complexities involved in the development of a single fertilized egg into the millions of specialized cells that constitute a human being. Although the cause of most birth defects is unknown, certain genetic and environmental factors increase the chance of birth defects developing. These factors include exposure to radiation Radiation and children Radiation injury is damage to tissues caused by exposure to ionizing radiation. Large doses of ionizing radiation can cause acute illness by reducing the production of blood cells and damaging... read more , certain drugs (see Table: Some Drugs That Can Cause Problems During Pregnancy* Some Drugs That Can Cause Problems During Pregnancy* More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy... read more ), alcohol Alcohol during pregnancy More than 50% of pregnant women take prescription or nonprescription (over-the-counter) drugs or use social drugs (such as tobacco and alcohol) or illicit drugs at some time during pregnancy... read more , nutritional deficiencies Drugs and dietary supplements There is much a pregnant woman can do to take care of herself during pregnancy. If she has any questions about diet, the use of drugs or nutritional supplements, physical activity, and sexual... read more , certain infections in the mother Infections During Pregnancy Most common infections that occur during pregnancy, such as those of the skin, urinary tract, and respiratory tract, cause no serious problems. However, some infections can be passed to the... read more , and genetic disorders Overview of Chromosome and Gene Disorders Chromosomes are structures within cells that contain a person's genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or... read more .

Some risks are avoidable. Others occur no matter how strictly a pregnant woman adheres to healthful living practices. Many birth defects develop before a woman knows she is pregnant.

Exposure to harmful substances (teratogens)

A teratogen is any substance that can cause or increase the chance of a birth defect. Teratogens include

Most pregnant women who are exposed to teratogens have newborns without abnormalities. Whether a birth defect occurs depends on when, how much, and how long the pregnant woman was exposed to the teratogen (see Exposures During Pregnancy Exposures During Pregnancy Some risk factors are present before women become pregnant. These risk factors include Certain physical characteristics, such as age, and social characteristics of women Problems in a previous... read more Exposures During Pregnancy ).

Exposure to a teratogen most commonly affects the fetal organ that is developing most rapidly at the time of exposure. For example, exposure to a teratogen during the time that certain parts of the brain are developing is more likely to cause a defect in those areas than exposure before or after this critical period.

Nutrition

Keeping a fetus healthy requires maintaining a nutritious diet Diet and weight There is much a pregnant woman can do to take care of herself during pregnancy. If she has any questions about diet, the use of drugs or nutritional supplements, physical activity, and sexual... read more . For example, insufficient folic acid (folate Folate Deficiency Folate deficiency is common. Because the body stores only a small amount of folate, a diet lacking in folate leads to a deficiency within a few months. Not eating enough raw leafy vegetables... read more ) in the diet increases the chance that a fetus will develop spina bifida or other abnormalities of the brain or spinal cord known as neural tube defects Neural Tube Defects and Spina Bifida Neural tube defects are a certain type of birth defect of the brain, spine, and/or spinal cord. Neural tube defects can result in nerve damage, learning disabilities, paralysis, and death. The... read more . Cleft lip Cleft Lip and Cleft Palate The most common birth defects of the skull and face are cleft lip and cleft palate, affecting about 2 of every 1,000 babies. Cleft lip is a separation of the upper lip, usually just below the... read more Cleft Lip and Cleft Palate (a separation of the upper lip) or cleft palate Cleft Lip and Cleft Palate The most common birth defects of the skull and face are cleft lip and cleft palate, affecting about 2 of every 1,000 babies. Cleft lip is a separation of the upper lip, usually just below the... read more Cleft Lip and Cleft Palate (a split in the roof of the mouth) is also more likely to develop.

Genetic and chromosomal factors

However, many birth defects are caused by new chromosome abnormalities or gene mutations that arise in the child and were not inherited from the parents.

Birth defects caused by genetic factors often include more than just an obvious malformation of a single body part.

Infections

Certain infections in pregnant women can cause birth defects (see Infections During Pregnancy Infections During Pregnancy Most common infections that occur during pregnancy, such as those of the skin, urinary tract, and respiratory tract, cause no serious problems. However, some infections can be passed to the... read more ). Whether an infection causes a birth defect depends on the age of the fetus at the time of the exposure to the infection.

The infections that most often cause birth defects are

A woman can have one of these infections and not know it because some of these infections can cause few or no symptoms in adults.

Diagnosis of Birth Defects

  • Before birth, ultrasonography and sometimes magnetic resonance imaging, blood tests, amniocentesis, or chorionic villus sampling

  • After birth, physical examination, ultrasonography, computed tomography, magnetic resonance imaging, and blood tests

Before birth

  • Older age

  • Have had frequent miscarriages

  • Have had other children with chromosome abnormalities or birth defects or who died for unknown reasons

These women may need monitoring and special tests to find out whether their baby is developing normally.

Increasingly, birth defects are being diagnosed before the baby is born.

Sometimes blood tests can also help. For example, a high level of alpha-fetoprotein in the mother's blood may indicate a defect of the brain or spinal cord or certain other organs (Second-Trimester Screening Second-Trimester Screening Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including certain hereditary or spontaneous genetic... read more ). More recently, doctors are using a test called cell-free fetal DNA analysis. In this test, a sample of a pregnant woman's blood is analyzed to determine whether her fetus has certain genetic disorders. This test is based on the fact that the mother's blood contains a very small amount of DNA (genetic material) from the fetus. This test is called noninvasive prenatal screening Testing for chromosome and gene abnormalities Chromosomes are structures within cells that contain a person's genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or... read more (NIPS). NIPS can be used to detect an increased risk of trisomy 21 Down Syndrome (Trisomy 21) Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome 21... read more Down Syndrome (Trisomy 21) (Down syndrome), trisomy 13 Trisomy 13 Trisomy 13 is a chromosomal disorder caused by an extra chromosome 13 that results in severe intellectual disability and physical abnormalities. Trisomy 13 is caused by an extra chromosome 13... read more Trisomy 13 , or trisomy 18 Trisomy 18 Trisomy 18 is a chromosomal disorder caused by an extra chromosome 18 that results in intellectual disability and physical abnormalities. Trisomy 18 caused by an extra chromosome 18. Infants... read more Trisomy 18 and certain other chromosome disorders. Doctors usually do further testing when an increased risk of a gene abnormality is detected.

After birth

After birth, the doctor does a physical examination of the newborn Physical Examination of the Newborn The doctor usually gives the newborn a thorough physical examination within the first 24 hours of life. The examination begins with a series of measurements, including weight, length, and head... read more Physical Examination of the Newborn . During this examination, the doctor examines the newborn's skin, head and neck, heart and lungs, and abdomen and genitals and assesses the newborn's nervous system and reflexes. Some newborns have a physical appearance that suggests a certain disorder.

Treatment of Birth Defects

  • Sometimes surgery or drugs

Abnormal chromosomes or genes cannot be corrected.

Surgery can correct or help some birth defects. Drugs and surgery can be used to manage the symptoms caused by other defects.

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