Congenital anomalies are structural or functional anomalies present at birth that can cause physical disability, intellectual and developmental disabilities (IDDs), and other health problems. Some may be fatal, especially if not detected and treated early.

There are two main categories of congenital anomalies: structural and functional/developmental. This information focuses on structural congenital anomalies, their causes, their prevention, and their treatment. Functional/developmental congenital anomalies are addressed more completely in the IDDs content.

Some congenital anomalies affect many parts or processes in the body, leading to both structural and functional problems.

Researchers have identified thousands of different congenital anomalies. According to the Centers for Disease Control and Prevention (CDC), congenital anomalies are the leading cause of death for infants in the United States during the first year of life.

What are birth defects?

A birth defect is a problem that happens while a baby is developing in the mother's body. Most birth defects happen during the first 3 months of pregnancy. One out of every 33 babies in the United States is born with a birth defect.

A birth defect may affect how the body looks, works, or both. Some birth defects like cleft lip or neural tube defects are structural problems that can be easy to see. Others, like heart disease, are found using special tests. Birth defects can range from mild to severe. How a birth defect affects a child's life depends mostly on which organ or body part is involved and how severe the defect is.

What causes birth defects?

For some birth defects, researchers know the cause. But for many birth defects, the exact cause is unknown. Researchers think that most birth defects are caused by a complex mix of factors, which can include

• Genetics. One or more genes might have a change or mutation that prevents them from working properly. For example, this happens in Fragile X syndrome. With some defects, 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. This is what happens in Turner syndrome. In other cases, such as with Down syndrome, the child has an extra chromosome.
• Exposures to medicines, chemicals, or other toxic substances. For example, alcohol misuse can cause fetal alcohol spectrum disorders.
• Infections during pregnancy. For example, infection with Zika virus during pregnancy can cause a serious defect in the brain.
• Lack of certain nutrients. Not getting enough folic acid before and during pregnancy is a key factor in causing neural tube defects.

Who is at risk of having a baby with birth defects?

Certain factors may might increase the chances of having a baby with a birth defect, such as

• Smoking, drinking alcohol, or taking certain "street" drugs during pregnancy
• Having certain medical conditions, such as obesity or uncontrolled diabetes, before and during pregnancy
• Taking certain medicines
• Having someone in your family with a birth defect. To learn more about your risk of having a baby with a birth defect, you can talk with a genetic counselor,
• Being an older mother, typically over the age of 34 years

How are birth defects diagnosed?

Health care providers can diagnose some birth defects during pregnancy, using prenatal testing. That's why it important to get regular prenatal care.

Other birth defects may not be found until after the baby is born. Providers may find them through newborn screening. Some defects, such as club foot, are obvious right away. Other times, the health care provider may not discover a defect until later in life, when the child has symptoms.

What are the treatments for birth defects?

Children with birth defects often need special care and treatments. Because the symptoms and problems caused by birth defects vary, the treatments also vary. Possible treatments may include surgery, medicines, assistive devices, physical therapy, and speech therapy.

Often, children with birth defects need a variety of services and may need to see several specialists. The primary health care provider can coordinate the special care that the child needs.

Can birth defects be prevented?

Not all birth defects can be prevented. But there are things you can do before and during pregnancy to increase your chance of having a healthy baby:

• Start prenatal care as soon as you think you might be pregnant, and see your health care provider regularly during pregnancy
• Get 400 micrograms (mcg) of folic acid every day. If possible, you should start taking it at least one month before you get pregnant.
• Don't drink alcohol, smoke, or use "street" drugs
• Talk to your health care provider about any medicines you are taking or thinking about taking. This includes prescription and over-the-counter medicines, as well as dietary or herbal supplements.
• Learn how to prevent infections during pregnancy
• If you have any medical conditions, try to get them under control before you get pregnant

Birth defects are common, costly, and critical conditions that affect 1 in every 33 babies born in the United States each year. Read more about what we have learned about birth defects and how women can improve their chances of having a baby born without a birth defect.

Birth Defects Are Common

Every 4 ½ minutes, a baby is born with a birth defect in the United States. That means nearly 120,000 babies are affected by birth defects each year.

Birth defects are structural changes present at birth that can affect almost any part or parts of the body (e.g., heart, brain, foot). They may affect how the body looks, works, or both. Birth defects can vary from mild to severe. The well-being of each child affected with a birth defect depends mostly on which organ or body part is involved and how much it is affected. Depending on the severity of the defect and what body part is affected, the expected lifespan of a person with a birth defect may or may not be affected.

Identifying Birth Defects

A birth defect can be found before birth, at birth, or any time after birth. Most birth defects are found within the first year of life. Some birth defects (such as cleft lip) are easy to see, but others (such as heart defects or hearing loss) are found using special tests, such as echocardiograms (an ultrasound picture of the heart), x-rays or hearing tests.

Causes

Birth defects can occur during any stage of pregnancy. Most birth defects occur in the first 3 months of pregnancy, when the organs of the baby are forming. This is a very important stage of development. However, some birth defects occur later in pregnancy. During the last six months of pregnancy, the tissues and organs continue to grow and develop.

For some birth defects, like fetal alcohol syndrome, we know the cause. But for most birth defects, we don’t know what causes them. For most birth defects, we think they are caused by a complex mix of factors. These factors include our genes (information inherited from our parents), our behaviors, and things in the environment. But, we don’t fully understand how these factors might work together to cause birth defects.

While we still have more work to do, we have learned a lot about birth defects through past research. For example, some things might increase the chances of having a baby with a birth defect, such as:

• Smoking, drinking alcohol, or taking certain drugs during pregnancy.
• Having certain medical conditions, such as being obese or having uncontrolled diabetes before and during pregnancy.
• Taking certain medications, such as isotretinoin (a drug used to treat severe acne).
• Having someone in your family with a birth defect. To learn more about your risk of having a baby with a birth defect, you can talk with a clinical geneticist or a genetic counselor.
• Having certain infections during pregnancy such as Zika virus and cytomegalovirus.
• Experiencing fever greater than 101^oF or having an elevated body temperature due to heat exposure.
• Being an older mother, as the risk of chromosomal abnormalities increases with age.

Having one or more of these risks doesn’t mean you’ll have a pregnancy affected by a birth defect. Also, women can have a baby born with a birth defect even when they don’t have any of these risks. It is important to talk to your doctor about what you can do to lower your risk.

Prevention

Not all birth defects can be prevented. But, there are things that a woman can do before and during pregnancy to increase her chance of having a healthy baby:

• Be sure to see your healthcare provider regularly and start prenatal care as soon as you think you might be pregnant.
• Get 400 micrograms (mcg) of folic acid every day, starting at least one month before getting pregnant.
• Don’t drink alcohol or smoke.
• Talk to a healthcare provider about any medications you are taking or thinking about taking. This includes prescription and over-the-counter medications and dietary or herbal supplements. Don’t stop or start taking any type of medication without first talking with a doctor.
• Know how to prevent infections during pregnancy.
• Be proactive in identifying and treating fever when ill or after getting a vaccine. Treat fevers higher than 101^oF with Tylenol® (or store brand acetaminophen), and avoid hot tubs, saunas, or other environments that might cause overheating.
• If possible, be sure any medical conditions are under control, before becoming pregnant. Some conditions, such as diabetes, can increase the risk for birth defects.

Living with a Birth Defect

Babies who have birth defects often need special care and interventions to survive and to thrive developmentally. State birth defects tracking programs provide one way to identify and refer children as early as possible for services they need. Early intervention is vital to improving outcomes for these babies. If your child has a birth defect, you should ask his or her doctor about local resources and treatment. Geneticists, genetic counselors, and other specialists are another resource.

In the United States

• Birth defects affect one in every 33 babies (about 3% of all babies) born in the United States each year.
• Birth defects are the leading cause of infant deaths, accounting for 20% of all infant deaths.

Brain/Spine Defects

Eye Defects

Heart Defects

Mouth/Face Defects

Stomach/Intestine Defects

Muscle/Bone Defects

Chromosome (Gene) Defects

There are two main categories of congenital anomalies.

Structural Congenital Anomalies

Structural congenital anomalies 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
• Atypical 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 Congenital Anomalies

Functional or developmental congenital anomalies 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 congenital anomalies 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 congenital anomalies affect many parts or processes in the body, leading to both structural and functional problems.

This information focuses on structural congenital anomalies, their causes, their prevention, and their treatment. Functional/developmental congenital anomalies are addressed more completely in the intellectual and developmental disabilities content.

Most brain malformations begin long before a baby is born. Something damages the developing nervous system or causes it to develop abnormally. Sometimes it's a genetic problem. In other cases, exposure to certain medicines, infections, or radiation during pregnancy interferes with brain development. Parts of the brain may be missing, abnormally small or large, or not fully developed.

Treatment depends upon the problem. In many cases, treatment only helps with symptoms. It may include antiseizure medicines, shunts to drain fluid from the brain, and physical therapy.

There are head malformations that do not involve the brain. Craniofacial disorders are the result of abnormal growth of soft tissue and bones in the face and head. It's common for new babies to have slightly uneven heads, but parents should watch the shape of their baby's head for possible problems.

Chiari malformations (CMs) are structural defects in the cerebellum. The cerebellum is the part of the brain that controls balance. With CM, brain tissue extends into the spinal canal. It can happen when part of the skull is too small, which pushes the brain tissue down. There are several types of CM. One type often happens in children who have neural tube defects. Some types cause no symptoms and don't need treatment. If you have symptoms, they may include

• Neck pain
• Balance problems
• Numbness or other abnormal feelings in the arms or legs
• Dizziness
• Vision problems
• Difficulty swallowing
• Poor hand coordination

Doctors diagnose CM using imaging tests. Medicines may ease some symptoms, such as pain. Surgery is the only treatment available to correct or stop the progression of nerve damage.

Cleft lip and cleft palate are birth defects that occur when a baby's lip or mouth do not form properly. They happen early during pregnancy. A baby can have a cleft lip, a cleft palate, or both.

A cleft lip happens if the tissue that makes up the lip does not join completely before birth. This causes an opening in the upper lip. The opening can be a small slit or a large opening that goes through the lip into the nose. It can be on one or both sides of the lip or, rarely, in the middle of the lip.

Children with a cleft lip also can have a cleft palate. The roof of the mouth is called the "palate." With a cleft palate, the tissue that makes up the roof of the mouth does not join correctly. Babies may have both the front and back parts of the palate open, or they may have only one part open.

Children with a cleft lip or a cleft palate often have problems with feeding and talking. They also might have ear infections, hearing loss, and problems with their teeth.

Often, surgery can close the lip and palate. Cleft lip surgery is usually done before age 12 months, and cleft palate surgery is done before 18 months. Many children have other complications. They may need additional surgeries, dental and orthodontic care, and speech therapy as they get older. With treatment, most children with clefts do well and lead a healthy life.

What are congenital heart defects?

Congenital heart defects (CHDs) are problems with the structure of the heart. "Congenital" means that that the problems are present at birth. These defects happen when a baby's heart doesn't develop normally during pregnancy. Congenital heart defects are the most common type of birth defect.

Congenital heart defects can change the way the heart pumps blood. They may make blood flow too slowly, go the wrong way, or block it completely.

There are many types of congenital heart defects. They can happen in one or more parts of the heart. The most common types are:

• Septal defects ("hole in the heart") - openings in the wall between the left and right sides of the heart
• Heart valve defects - problems with the valves that control the flow of blood through the heart
• Defects in the large blood vessels that carry blood in and out of the heart

Congenital heart defects can range from very mild problems that never need treatment to life-threatening problems at birth. The most serious congenital heart defects are called critical congenital heart disease. Babies with these defects usually need surgery in the first year of life. But the symptoms of milder heart defects may not show up until childhood or adulthood.

What causes congenital heart defects?

Researchers often don't know what causes congenital heart defects. They do know that changes in a baby's genes sometimes cause a heart defect. The changed genes may come from the parents, or the changes may happen during pregnancy.

Who is more likely to have a baby with a congenital heart defect?

Several things may increase the chance that your baby has a congenital heart defect, such as:

• Your health before and during pregnancy, including
  • Having diabetes before pregnancy or developing it in the first 3 months of pregnancy (diabetes that develops later in pregnancy isn't a major risk for heart defects). Carefully controlling your blood sugar before and during pregnancy can lower your baby's risk of congenital heart defects.
  • Having phenylketonuria (PKU), a rare inherited disorder that affects how the body uses a protein in foods. If you have PKU, eating a low-protein diet before getting pregnant can lower your baby's risk of having a congenital heart defect.
  • Having rubella (German measles) during pregnancy.
• Your contact with certain substances during pregnancy, including
  • Smoking or secondhand smoke (breathing smoke from another smoker).
  • Certain medicines, such as angiotensin-converting (ACE) inhibitors for high blood pressure and retinoic acids for acne. If you're pregnant or plan to get pregnant, talk with your health care provider about all the medicines you take.
• Your family history and genetics. In most cases, congenital heart defects don't run in families. But your chance of having a baby with a congenital heart defect does go up if you or the other parent has a congenital heart defect, or if you already have a child with a congenital heart defect.

What are the symptoms of congenital heart defects?

Congenital heart defects don't cause pain. The signs and symptoms are different, depending on the type and number of defects and how serious they are.

Common signs and symptoms of congenital heart defects include:

• Cyanosis - a bluish color to the skin, lips, and fingernails. It happens when there isn't enough oxygen in the blood
• Fatigue - your baby may be unusually sleepy and may become very tired during feedings
• Poor blood flow
• Fast or difficult breathing
• Heart murmur - an unusual sound between heartbeats

What other problems do congenital heart defects cause?

Congenital heart defects don't always cause other problems. If they do, which problems you have would depend on the type and number of defects and how serious the defects are.

Children with congenital heart defects are more likely to:

• Be smaller than other children
• Have problems or delays in mental, and emotional growth, and behavior, such as:
  • Speech and language problems
  • Attention deficit hyperactivity disorders (ADHD)

People with congenital heart defects may develop other health conditions, including:

• Endocarditis - an infection of lining of the heart and valves
• Arrhythmia - a problem with the rate or rhythm of your heartbeat
• Heart failure - when your heart can't pump enough blood to the body
• Pulmonary hypertension - high blood pressure in your lungs
• Kidney and liver disease

How are congenital heart defects diagnosed?

• Before a baby is born, your provider may use ultrasound pictures of the baby's heart to look for heart defects. This is called a fetal echocardiogram. It's done between weeks 18 and 22 of pregnancy.
• During the first few days after birth, all newborns are checked for congenital heart defects. A pulse oximeter is clipped to your baby's hands or feet to measure blood oxygen. If it shows low levels of blood oxygen, more tests will be needed to find out if your baby has a heart defect.
• To diagnose congenital heart defects in babies, children, and adults, a provider may use many tools, including:
  • A physical exam.
  • Certain heart tests to see how the heart is working.
  • Genetic testing to see if certain gene problems caused the defect.

What are the treatments for congenital heart defects?

Treatment depends on the type of congenital heart defect and how serious it is. Possible treatments include:

• Cardiac catheterization to repair simple defects, such as a small hole in the inside wall of the heart. A catheterization uses a thin tube guided through a vein and into the heart.
• Heart surgery may be needed to:
  • Repair defects in the heart and blood vessels.
  • Repair or replace a heart valve.
  • Place a device in the chest to help the heart pump blood.
  • Do a heart transplant.
• Medicine is often used if your baby has a specific type of congenital heart defect called patent ductus arteriosus.

All children and adults who have congenital heart defects need regular follow-up care from a cardiologist (a doctor who specializes in heart diseases) throughout their life, even if their defect was repaired.

Some people may need several heart surgeries or catheterizations over the years. They may also need to take medicines to help their hearts work as well as possible.

Craniofacial is a medical term that relates to the bones of the skull and face. Craniofacial abnormalities are birth defects of the face or head. Some, like cleft lip and palate, are among the most common of all birth defects. Others are very rare. Most of them affect how a person's face or head looks. These conditions may also affect other parts of the body.

Treatment depends on the type of problem. Plastic and reconstructive surgery may help the person's appearance.

Alcohol can harm your baby at any stage during a pregnancy. That includes the earliest stages, before you even know you are pregnant. Drinking during pregnancy can cause a group of conditions called fetal alcohol spectrum disorders (FASDs). Children who are born with FASD can have a mix of problems, such as medical, behavioral, educational, and social problems. The kinds of problems they have depend on which type of FASD they have. The problems could include :

• Abnormal facial features, such as a smooth ridge between the nose and upper lip
• Small head size
• Shorter-than-average height
• Low body weight
• Poor coordination
• Hyperactive behavior
• Difficulty with attention and memory
• Learning disabilities and difficulty in school
• Speech and language delays
• Intellectual disability or low IQ
• Poor reasoning and judgment skills
• Sleep and sucking problems as a baby
• Vision or hearing problems
• Problems with the heart, kidneys, or bones

Fetal alcohol syndrome (FAS) is the most serious type of FASD. People with fetal alcohol syndrome have facial abnormalities, including wide-set and narrow eyes, growth problems and nervous system abnormalities.

Diagnosing FASD can be hard because there is no medical test, like a blood test, for it. The health care provider will make a diagnosis by looking at the child's signs and symptoms and asking whether the mother drank alcohol during pregnancy.

FASDs last a lifetime. There is no cure for FASDs, but treatments can help. These include medicines to help with some symptoms, medical care for health problems, behavior and education therapy, and parent training. A good treatment plan is specific to the child's problems. It should include close monitoring, follow-ups, and changes when needed.

Certain "protective factors" can help reduce the effects of FASDs and help people who have them reach their full potential. They include:

• Diagnosis before 6 years of age
• Loving, nurturing, and stable home environment during the school years
• Absence of violence around them
• Involvement in special education and social services

There is no known safe amount of alcohol during pregnancy. To prevent FASDs, you should not drink alcohol while you are pregnant, or when you might get pregnant.

A normal pregnancy lasts nine months. Each three-month period of pregnancy is called a trimester. During each trimester, the fetus grows and develops. Regular medical checkups and prenatal tests are very important. They can:

• Help keep you and your baby healthy
• Spot problems with your baby (if there are any). In some cases, health care professionals can treat the problem before your baby is born. But even when they cannot, it can still be helpful to know about the problem early on. That gives you time to learn about your baby's condition and prepare for any challenges you may face after the baby is born.
• Prevent problems during delivery. For example, if your baby is breech (bottom first or feet first, instead of head first), you may need to have a Cesarean section to avoid complications.

Besides getting medical care, there are other things you can do to keep your baby as healthy as possible. It's important not to drink or smoke. Try to eat a healthy diet and make sure to take care of any health problems you have during pregnancy.

A genetic brain disorder is caused by a variation or a mutation in a gene. A variation is a different form of a gene. A mutation is a change in a gene. Genetic brain disorders affect the development and function of the brain.

Some genetic brain disorders are due to random gene mutations or mutations caused by environmental exposure, such as cigarette smoke. Other disorders are inherited, which means that a mutated gene or group of genes is passed down through a family. They can also be due to a combination of both genetic changes and other outside factors.

Some examples of genetic brain disorders include

• Leukodystrophies
• Phenylketonuria
• Tay-Sachs disease
• Wilson disease

Many people with genetic brain disorders fail to produce enough of certain proteins that influence brain development and function. These brain disorders can cause serious problems that affect the nervous system. Some have treatments to control symptoms. Some are life-threatening.

Genes are the building blocks of heredity. They are passed from parent to child. They hold DNA, the instructions for making proteins. Proteins do most of the work in cells. They move molecules from one place to another, build structures, break down toxins, and do many other maintenance jobs.

Sometimes there is a mutation, a change in a gene or genes. The mutation changes the gene's instructions for making a protein, so the protein does not work properly or is missing entirely. This can cause a medical condition called a genetic disorder.

You can inherit a gene mutation from one or both parents. A mutation can also happen during your lifetime.

There are three types of genetic disorders:

• Single-gene disorders, where a mutation affects one gene. Sickle cell anemia is an example.
• Chromosomal disorders, where chromosomes (or parts of chromosomes) are missing or changed. Chromosomes are the structures that hold our genes. Down syndrome is a chromosomal disorder.
• Complex disorders, where there are mutations in two or more genes. Often your lifestyle and environment also play a role. Colon cancer is an example.

Genetic tests on blood and other tissue can identify genetic disorders.

What is genetic testing?

Genetic testing is a type of medical test that looks for changes in your DNA. DNA is short for deoxyribonucleic acid. It contains the genetic instructions in all living things. Genetic tests analyze your cells or tissue to look for any changes in

• Genes, which are parts of DNA that carry the information needed to make a protein
• Chromosomes, which are thread-like structures in your cells. They contain DNA and proteins.
• Proteins, which do most of the work in your cells. Testing can look for changes in the amount and activity level of proteins. If it finds changes, it might be due to changes in your DNA.

Why is genetic testing done?

Genetic testing may be done for many different reasons, including to

• Find genetic diseases in unborn babies. This is one type of prenatal testing.
• Screen newborn babies for certain treatable conditions
• Lower the risk of genetic diseases in embryos that were created using assisted reproductive technology
• Find out if you carry a gene for a certain disease that could be passed on to your children. This is called carrier testing.
• See whether you are at increased risk of developing a specific disease. This may be done for a disease that runs in your family.
• Diagnose certain diseases
• Identify genetic changes that may be causing or contributing to a disease that you were already diagnosed with
• Figure out how severe a disease is
• Help guide your doctor in deciding the best medicine and dosage for you. This is called pharmacogenomic testing.

How is genetic testing done?

Genetic tests are often done on a blood or cheek swab sample. But they may also be done on samples of hair, saliva, skin, amniotic fluid (the fluid that surrounds a fetus during pregnancy), or other tissue. The sample is sent to a laboratory. There, a lab technician will use one of several different techniques to look for genetic changes.

What are the benefits of genetic testing?

The benefits of genetic testing include

• Helping doctors make recommendations for treatment or monitoring
• Giving you more information for making decisions about your health and your family's health:
  • If you find out that you are at risk for a certain disease, you might take steps to lower that risk. For example, you may find out that you should be screened for a disease earlier and more often. Or you might decide to make healthy lifestyle changes.
  • If you find out that you are not at risk for a certain disease, then you can skip unnecessary checkups or screenings
  • A test could give you information that helps you make decisions about having children
• Identifying genetic disorders early in life so treatment can be started as soon as possible

What are the drawbacks of genetic testing?

The physical risks of the different types of genetic testing are small. But there can be emotional, social, or financial drawbacks:

• Depending on the results, you may feel angry, depressed, anxious, or guilty. This can be especially true if you are diagnosed with a disease that does not have effective treatments.
• You may be worried about genetic discrimination in employment or insurance
• Genetic testing may give you limited information about a genetic disease. For example, it cannot tell you whether you will have symptoms, how severe a disease might be, or whether a disease will get worse over time.
• Some genetic tests are expensive, and health insurance might only cover part of the cost. Or they may not cover it at all.

How do I decide whether to be tested?

The decision about whether to have genetic testing is complex. In addition to discussing the test with your health care provider, you can meet with a genetic counselor. Genetic counselors have specialized degrees and experience in genetics and counseling. They can help you understand the tests and weigh the risks and benefits. If you do get a test, they can explain the results and make sure that you have the support that you need.

Neural tube defects are birth defects of the brain, spine, or spinal cord. They happen in the first month of pregnancy, often before a woman even knows that she is pregnant. The two most common neural tube defects are spina bifida and anencephaly. In spina bifida, the fetal spinal column doesn't close completely. There is usually nerve damage that causes at least some paralysis of the legs. In anencephaly, most of the brain and skull do not develop. Babies with anencephaly are usually either stillborn or die shortly after birth. Another type of defect, Chiari malformation, causes the brain tissue to extend into the spinal canal.

The exact causes of neural tube defects aren't known. You're at greater risk of having an infant with a neural tube defect if you

• Have obesity
• Have poorly controlled diabetes
• Take certain antiseizure medicines

Getting enough folic acid, a type of B vitamin, before and during pregnancy prevents most neural tube defects.

Neural tube defects are usually diagnosed before the infant is born, through lab or imaging tests. There is no cure for neural tube defects. The nerve damage and loss of function that are present at birth are usually permanent. However, a variety of treatments can sometimes prevent further damage and help with complications.

Prenatal testing provides information about your baby's health before he or she is born. Some routine tests during pregnancy also check on your health. At your first prenatal visit, your health care provider will test for a number of things, including problems with your blood, signs of infections, and whether you are immune to rubella (German measles) and chickenpox.

Throughout your pregnancy, your health care provider may suggest a number of other tests, too. Some tests are suggested for all women, such as screenings for gestational diabetes, Down syndrome, and HIV. Other tests might be offered based on your

• Age
• Personal or family medical history
• Ethnic background
• Results of routine tests

There are two types of tests:

• Screening tests are tests that are done to see if you or your baby might have certain problems. They evaluate risk, but do not diagnose problems. If your screening test result is abnormal, it does not mean that there is a problem. It means that more information is needed. Your health care provider can explain what the test results mean and possible next steps. You may need diagnostic testing.
• Diagnostic tests show whether or not you or your baby have a certain problem.

It is your choice whether or not to get the prenatal tests. You and your health care provider can discuss the risks and benefits of the tests, and what kind of information the tests can give you. Then you can decide which ones are right for you.

CDC estimates that congenital anomalies occur in about 1 in every 33 infants born in the United States each year.

Congenital anomalies can occur during any pregnancy, but some factors increase the risk. The following situations place pregnant people at higher risk of having a child with a congenital anomaly:

• Lack of folic acid. People 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 people of childbearing age take folic acid every day.
• Drinking alcohol. Drinking alcohol during pregnancy can lead to a variety of problems, including congenital anomalies. For example, using alcohol can lead to a fetal alcohol spectrum disorder, which is characterized by intellectual or developmental disabilities (IDD), physical challenges, and behavioral problems. There is no safe level of alcohol consumption during pregnancy.
• 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 congenital anomalies, such as cleft lip or cleft palate, are caused by smoking during pregnancy.
• Using drugs. Using drugs during pregnancy can increase the risk of various congenital anomalies, including IDDs and behavioral problems, as well as pregnancy loss and stillbirth.
• Medication use. Certain medications are known to cause congenital anomalies 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 congenital anomalies. 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, most medications currently used by pregnant people have not been tested for safety or efficacy in pregnant people. People 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.
• Infections. People who get certain infections during pregnancy are at higher risk for having a child with congenital anomalies. Some of the more common infections linked to congenital anomalies 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 atypically small.
• Obesity or uncontrolled diabetes. NICHD research found that the risk of newborn heart defects and NTDs increased with maternal obesity. Additional NICHD research suggest that children of parents with obesity may be at risk for developmental delays. Obesity is also associated with 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).
• Exposure to things in the environment. Pregnant people who breathe in, eat, drink, or get things into their bodies in other ways may also be at increased risk of congenital anomalies. For example, pregnant people who are exposed to high levels of radiation, such as cancer treatments, are at higher risk for congenital anomalies in their infants.⁹ Handling or breathing in certain chemicals can also increase the risk of congenital anomalies.

Different congenital anomalies have different causes, and the causes of many congenital anomalies remain unknown.

A specific condition might be caused by one or more of the following primary problems:

• 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 congenital anomalies 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 congenital anomaly called microcephaly, in which the brain and skull are atypically small. Zika infection in pregnancy is linked to other structural problems with the brain as well.
• Exposure to medications, chemicals, or other agents during pregnancy. The infants whose mothers took thalidomide are examples of an exposure leading to congenital anomalies. Other examples include exposure to rubella (also called German measles) and toxic chemicals, such as hydrocarbons.