Birth defects are structural (how the body is built) or functional (how the body works) abnormalities present at birth that can cause physical disability, intellectual and developmental disorders, and other health problems. This information focuses on structural birth defects, such as heart, limb, or brain malformations, their causes, their prevention, and their treatments. Functional/developmental birth defects are addressed more completely in the Intellectual and Developmental Disabilities (IDD) information.
There are two main categories of birth defects: structural birth defects and functional/developmental birth defects. This information focuses on structural birth defects, their causes, their prevention, and their treatment. Functional/developmental birth defects are addressed more completely in the IDDs content.
Researchers have identified thousands of different birth defects, and some are more disruptive than others. If not detected and treated quickly, some can be fatal or cause lifelong disabilities. Currently, the Centers for Disease Control and Prevention notes that birth defects are the leading cause of death for infants during the first year of life.
What are the types of birth defects?
There are two main categories of birth defects.
Structural Birth Defects
Structural birth defects are related to a problem with the structure of body parts. These can include:
- Cleft lip or cleft palate
- Heart defects, such as missing or misshaped valves
- Abnormal limbs, such as a clubfoot
- Neural tube defects, such as spina bifida, and problems related to the growth and development of the brain and spinal cord
Functional or Developmental Birth Defects
Functional or developmental birth defects are related to a problem with how a body part or body system works or functions. These problems can include:
- Nervous system or brain problems. These include intellectual and developmental disabilities, behavioral disorders, speech or language difficulties, seizures, and movement trouble. Some examples of birth defects that affect the nervous system include Down syndrome, Prader-Willi syndrome, and Fragile X syndrome.
- Sensory problems. Examples include hearing loss and visual problems, such as blindness or deafness.
- Metabolic disorders. These involve problems with certain chemical reactions in the body, such as conditions that limit the body’s ability to rid itself of waste materials or harmful chemicals. Two common metabolic disorders are phenylketonuria and hypothyroidism.
- Degenerative disorders. These are conditions that might not be obvious at birth but cause one or more aspects of health to steadily get worse. Examples of degenerative disorders are muscular dystrophy and X-linked adrenoleukodystrophy, which leads to problems of the nervous system and the adrenal glands and was the subject of the movie “Lorenzo’s Oil.”
Some birth defects affect many parts or processes in the body, leading to both structural and functional problems.
What causes birth defects?
Different birth defects have different causes, and the causes of many birth defects remain unknown.
A specific condition might be caused by one or more of the following primary problems:1
- Genetic problems. One or more genes might have a change or mutation that results in them not working properly, such as in Fragile X syndrome. Similarly, a gene or part of the gene might be missing.
- Chromosomal problems. In some cases, a chromosome or part of a chromosome might be missing, such as in Turner syndrome, when a female is missing an X chromosome. Other birth defects result from having an extra chromosome, such as in Klinefelter syndrome and Down syndrome.
- Infections. Women who get certain infections during pregnancy are at higher risk for having a child with birth defects. For example, infection with Zika virus during pregnancy is linked with the birth defect called microcephaly, in which the brain and skull are smaller than normal. Zika infection in pregnancy is linked to other structural problems with the brain as well. Our Pregnancy topic has more information on infections that can cause birth defects and other problems in newborns and on ways to prevent them during pregnancy, and CDC provides tips for preventing infections before and during pregnancy.
- Exposure to medications, chemicals, or other agents during pregnancy. The infants whose mothers took thalidomide are examples of an exposure leading to birth defects. Other examples include exposure to rubella (also called German measles) and toxic chemicals, such as hydrocarbons.2
How many people are affected by/at risk for birth defects?
CDC estimates that birth defects occur in about 1 in every 33 infants born in the United States each year.1
Birth defects can occur during any pregnancy, but some factors increase the risk for birth defects. The following situations place pregnant women at higher risk of having a child with a birth defect:2
- Lack of folic acid. Women who are pregnant or who could become pregnant should take 400 micrograms of folic acid every day to prevent neural tube defects (NTDs). However, according to the Centers for Disease Control and Prevention (CDC), only 2 out of every 5 women of childbearing age take folic acid every day.3
- Drinking alcohol.Drinking alcohol during pregnancy can lead to a variety of problems, including birth defects. For example, using alcohol can lead to fetal alcohol syndrome, which is characterized by intellectual or developmental disability (IDD), physical challenges, and behavioral problems. There is no safe level of alcohol consumption during pregnancy.4
- Smoking cigarettes. Smoking cigarettes during pregnancy can lead to a variety of problems, including lung problems such as asthma. Evidence also strongly suggests that certain birth defects, such as problems with the heart and intestines, are caused by smoking during pregnancy.5
- Using drugs. Using drugs during pregnancy can increase the risk of various birth defects, including IDDs and behavioral problems, as well as pregnancy loss and stillbirth.6
- Medication use. Certain medications are known to cause birth defects if taken during pregnancy. Thalidomide, which is currently used to treat certain cancers and other serious conditions, was once sold as a treatment for morning sickness until it was discovered that it caused severe birth defects. Infants whose mothers took thalidomide had a range of structural and functional problems, including misshapen ears and shortened limbs. Although the thalidomide situation led to much stricter controls on drugs used during pregnancy, the majority of medications currently used by pregnant women have not been tested for safety or efficacy in pregnant women. Addressing this issue is the primary focus of NICHD’s Obstetric-Fetal Pharmacology Research Units Network. Women who are pregnant or who might become pregnant should discuss all medications, both prescription and over-the-counter, and supplements they take with their health care providers.7
- Infections. Women who get certain infections during pregnancy are at higher risk for having a child with birth defects. Some of the more common infections that are linked to birth defects are cytomegalovirus, a common virus that spreads through body fluids and usually causes no symptoms in healthy people, and toxoplasmosis, a parasitic infection that spreads through contact with cat feces, raw meat, and contaminated food and water. Zika virus infection is linked to microcephaly in newborn babies—a condition in which the brain and skull are smaller than normal.
- Obesity or uncontrolled diabetes. NICHD research found that the risk of newborn heart defects and neural tube defects increased with maternal obesity. Additional NICHD research suggest that children of obese parents may be at risk for developmental delays. Obesity is also associated with other health problems and long-term health issues. Poorly controlled blood sugar places women at higher risk of having a baby who is too large, has breathing problems, or has other poor health outcomes. These outcomes are likely regardless of whether the woman had diabetes before she got pregnant (type 1 or 2 diabetes) or whether she developed diabetes during pregnancy (gestational diabetes).8
- Exposure to things in the environment. Pregnant women who breathe in, eat, drink, or get things into their bodies in other ways may also be at increased risk of birth defects. For example, pregnant women who are exposed to high levels of radiation, such as cancer treatments, are at higher risk for birth defects in their infants.9 Handling or breathing in certain chemicals can also increase the risk of birth defects.10
How do health care providers diagnose birth defects?
Diagnosis of birth defects depends on the specific problem and parts or systems of the body that are affected.
Many structural problems, such as club foot or cleft palate, are detected and diagnosed after a physical examination of the baby immediately after birth. For other conditions, newborn screening or prenatal testing is the only way to detect and diagnose problems.
This information focuses on structural birth defects, their causes, their prevention, and their treatments. Functional/developmental birth defects are addressed more completely in the intellectual and developmental disabilities content and in condition-specific topics.
Newborn Screening
Newborn screening, a process that tests infants’ blood for different health conditions, including many birth defects, provides one method of detecting problems. Newborn screening does not diagnose any specific conditions but detects that a problem may exist. By detecting problems immediately after birth, conditions can be diagnosed and treated before they have lifelong effects.
In addition, newborn screening routinely includes test for hearing problems, as well as pulse oximetry (test of baby’s pulse rate and blood oxygen levels) to detect critical congenital heart defects.1
Infants who are at high risk for certain conditions—for example, because of their family history—can undergo additional testing at birth to detect these conditions and treat them if needed. This type of screening has been effective in detecting some cases of Menkes disease, allowing for treatment to begin before health problems occur.
Prenatal Screening
During pregnancy, women have routine tests, such as blood and urine tests, to check for diabetes, signs of infection, or disorders of pregnancy such as preeclampsia. Blood tests also measure the levels of certain substances in a woman’s blood that determine the risk of the fetus for certain chromosomal disorders and neural tube defects. Ultrasound screenings, creating a picture using sound, allow providers to view the developing fetus in the womb. Some birth defects, such as spina bifida, are detectable on ultrasounds.
Health care providers recommend that certain pregnant women, including those who are older than 35 years of age and those with a family history of certain conditions, get additional prenatal tests to screen for birth defects. Prenatal detection allows doctors to start treatment as early as possible for some birth defects.
Noninvasive prenatal testing (NIPT)
NIPT is not a routine prenatal test but is used when a routine test suggests that the fetus may have a chromosomal disorder, such as having an extra or missing chromosome in each cell, which occurs in disorders such as Down syndrome, Patau syndrome, and Edwards syndrome.
NIPT analyzes the placental DNA present in the mother’s blood; it does not require cell samples from inside the womb.
Currently, experts recommend NIPT only for high-risk pregnancies.4 This method does not detect open neural tube defects, nor does it predict late pregnancy complications.
Amniocentesis
Amniocentesis (pronounced am-nee-oh-sen-TEE-sis) is a test that is usually performed to determine whether a fetus has a genetic disorder. In this test, a doctor takes a small amount of fluid from the womb using a long needle. The fluid, called amniotic (pronounced am-nee-OT-ik) fluid, contains cells that have genetic material that is the same as the fetus’s genetic material. A laboratory grows the cells and then examines their genetic material for any problems. Some birth defects that can be detected with amniocentesis are Down syndrome and certain types of muscular dystrophy.
There is a slight risk of pregnancy loss with amniocentesis, so women should discuss the procedure with their health care provider before making a decision about the test.
Chorionic Villus Sampling (CVS)
This test extracts cells from inside the womb to determine whether the fetus has a genetic disorder. Using a long needle, the doctor takes cells from the chorionic villi (pronounced KOHR-ee-on-ik VILL-i), which are tissues in the placenta, the organ in the womb that nourishes the fetus. The genetic material in the chorionic villus cells is identical to that of the fetal cells.
Like amniocentesis, CVS can be used to test for chromosomal disorders and other genetic problems. CVS can be done earlier in pregnancy than amniocentesis, but it is also associated with a slightly higher risk of miscarriage than amniocentesis. Women who are considering CVS should discuss the test and the risks with her health care provider.
What are the treatments for birth defects?
Because the symptoms and problems caused by birth defects vary, treatments for birth defects also vary. Treatments range from medications and therapies to surgeries and assistive devices.
This information focuses on structural birth defects, their causes, their prevention, and their treatments. Functional/developmental birth defects are addressed more completely in the intellectual and developmental disabilities content and in the condition-specific topics.
For example:
- Steroid medications, such as prednisone, can help people with muscular dystrophy increase muscle strength, ability, and respiratory function and slow the progression of weakness. Physical therapy is also useful for building strength and reducing weakness.
- Infants with cerebral palsy may receive sensory-motor therapy using Velcro-covered “sticky mittens” to help them “snag” and explore objects they are unable to grasp in the hand.1
- Assistive devices include orthopedic braces to help patients with limb defects to walk and cochlear implants for hearing impairment.
- In the Management of Myelomeningocele Study (MOMS), conducted through NICHD’s Maternal-Fetal Surgery Network, researchers tested a surgical procedure to correct a severe form of spina bifida while the fetus was still in the womb. Although the surgery itself carried risks, it greatly reduced health complications for the infants who received it, including greater likelihood of being able to walk without assistance. Visit http://nichd.nih.gov/news/resources/spotlight/pages/021011-spina-bifida-MOMS.aspx for more information.
- Gene therapy approaches, in which a gene that is mutated or missing is replaced by a normal version of the gene, are being tested for a variety of genetic disorders. Some examples of disorders that are being treated successfully with gene therapy include genetic disorders of the immune system, the muscles, and the eyes. Recent NICHD-supported research on Duchenne muscular dystrophy used genome editing techniques to improve leg grip strength in a mouse model by “turning on” a gene for a specific protein used in muscles.2
Visit https://clinicaltrials.gov to search for ongoing trials of gene therapies and other treatments for different birth defects and genetic disorders.
