Overview of Birth Defects

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 weight Problems in a previous pregnancy, including the... read more ).

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.

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 A cleft is an opening that can form in the lip (cleft lip), roof of the mouth (cleft palate), or both if the tissue does not join together completely during pregnancy. Cleft lip and cleft palate... read more (a separation of the upper lip) or cleft palate Cleft Lip and Cleft Palate A cleft is an opening that can form in the lip (cleft lip), roof of the mouth (cleft palate), or both if the tissue does not join together completely during pregnancy. Cleft lip and cleft palate... read more (a split in the roof of the mouth) is also more likely to develop.

Obesity Obesity Obesity is excess body weight. Obesity is influenced by a combination of factors, which usually results in consuming more calories than the body needs. These factors may include physical inactivity... read more in the mother also increases the risk of a neural tube defect.

Chromosomes Chromosomes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more and genes Genes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more may be abnormal. These abnormalities may be inherited from the parents, who may either be affected by the abnormalities or who may be carriers of the genes that cause the abnormalities (see Overview of Chromosome and Gene 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... read more ). Carriers are people who have an abnormal gene for a disorder but who do not have any symptoms of the disorder.

However, many birth defects are caused by new chromosome abnormalities or gene mutations that arise in the fertilized egg 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.

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.

Before birth, doctors assess whether a woman is at increased risk of having a baby with a birth defect (Prenatal Diagnostic Testing Prenatal Diagnostic Testing 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 ). The chance is higher for women who have the following risk factors Risk Factors for Genetic Disorders or Birth Defects Genetic disorders are disorders caused by abnormalities in one or more genes or chromosomes. Some genetic disorders are hereditary and others are spontaneous. Hereditary genetic disorders are... read more :

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.

Ultrasonography Ultrasonography 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 of the fetus is commonly done during pregnancy. Magnetic resonance imaging Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more (MRI) of the fetus may also be done when indicated. These imaging tests can often detect specific birth defects.

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 (see 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... 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 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 , 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 and certain other chromosome abnormalities. Doctors usually do further testing when an increased risk of a gene abnormality is detected.

Amniocentesis Amniocentesis 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 (removing fluid from around the fetus) or chorionic villus sampling Chorionic Villus Sampling 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 (removing tissue from the sac around the developing fetus) may help confirm a suspected diagnosis. Genetic testing is done on the samples taken during these procedures.

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 . 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.

In the United States, most newborns undergo routine screening blood tests Newborn Screening Tests Many serious disorders that are not apparent at birth can nonetheless be detected by various screening tests. Early diagnosis and prompt treatment can reduce or prevent many disorders that may... read more to detect a number of metabolic disorders Overview of Hereditary Metabolic Disorders Hereditary metabolic disorders are inherited genetic conditions that cause metabolism problems. Heredity is the passing of genes from one generation to the next. Children inherit their parents'... read more and genetic disorders 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... read more .

Imaging tests, such as ultrasonography Ultrasonography Ultrasonography uses high-frequency sound (ultrasound) waves to produce images of internal organs and other tissues. A device called a transducer converts electrical current into sound waves... read more , computed tomography Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more (CT), and magnetic resonance imaging Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more (MRI), may be done based on the results of the physical examination and screening tests.