Like most expectant parents, you probably alternate between fantasies about a healthy baby and worries that your baby will have a health problem. Or perhaps you've been told through prenatal screening that your baby might be born with a birth defect.

Many parents assume that all birth defects are severe or even fatal, but the fact is that many are treatable, often immediately after birth — and sometimes even before the baby is born.

It's especially important to know the risk factors involved and how to prevent birth defects. However, it's also important to realize that most babies born with congenital defects are born to two healthy parents.

About Birth Defects

Birth defects are defined as abnormalities of structure, function, or body metabolism that are present at birth. Major birth defects are abnormalities that lead to developmental or physical disabilities or require medical or surgical treatment. There are more than 4,000 different known birth defects, ranging from minor to serious, and although many can be treated or cured, they're the leading cause of death in the first year of life.

According to the March of Dimes, about 150,000 babies are born with birth defects each year in the United States. The American College of Obstetricians and Gynecologists (ACOG) says that 3 out of every 100 babies born in the United States have some kind of major birth defect.

Birth defects can be caused by genetic, environmental, or unknown factors. For most birth defects, the cause is believed to be an interaction of a number of genetic and environmental factors.

Structural or metabolic defects are those in which a specific body part is missing or formed incorrectly; metabolic birth defects are those in which there is an inborn problem in body chemistry. The most common type of major structural defects are heart defects, which affect 1 in 150 babies in the United States.

Other common structural defects include spina bifida, cleft palate, clubfoot, and congenital dislocated hip.

Metabolic defects affect 1 in 3,500 babies and usually involve a missing or incorrectly formed enzyme (a protein necessary for processing chemical substances in the body). Most children with a metabolic birth defect do not have any visible abnormalities, but metabolic defects are usually harmful or can be even fatal. Metabolic defects include Tay-Sachs disease, a fatal disease that affects the central nervous system, and phenylketonuria (PKU), which affects the way the body processes protein.

Defects caused by congenital infections result when a mother gets an infection before or during the pregnancy. Infections that can cause birth defects include rubella (German measles), cytomegalovirus (CMV), syphilis, toxoplasmosis, Venezuelan equine encephalitis, parvovirus, and, rarely, chickenpox. None of these affect 100% of babies whose mothers are infected during pregnancy. If the mother is infected during early pregnancy, rubella carries the highest risk for birth defects (approximately 20%). Because of nearly universal immunization in the United States, rubella is very, very rare and the congenital rubella syndrome is almost never seen. CMV is probably the most common congenital infection and may be associated with intellectual disability (mental retardation) and hearing loss.

Other causes of birth defects include alcohol abuse by the mother. Although a few medications, such as medicines used for epilepsy, are associated with increased risks for certain birth defects, most commonly prescribed drugs are not associated with a significant risk of birth defects.

Causes

Most babies with birth defects are born to two parents with no obvious health problems or risk factors. A woman can do everything her doctor recommends to deliver a healthy child and still have a baby with a birth defect.

In fact, according to the March of Dimes, about 60% of birth defects have unknown causes. The rest are caused by environmental or genetic factors, or some combination of the two.

Genetics play a role in some birth defects. Every cell in the body has chromosomes containing genes that go a long way in determining a person's unique characteristics. One missing or faulty gene can cause a birth defect; this is significant when you consider that we each have about 25,000 genes per cell determining everything from the length of our toes to the color of our eyes.

Where do the faulty genes come from? A child inherits one of each pair of chromosomes (and one of each pair of the genes they contain) from each parent. Sometimes, a disease or defect can occur if only one parent passes along the gene for that disease (even though the child receives a normal gene from the other parent); this is called dominant inheritance and includes birth defects such as achondroplasia (a form of dwarfism) and Marfan syndrome (a disorder characterized by abnormally long fingers, arms, and legs).

Some birth defects occur only when two healthy parents each pass along a faulty gene for the same disease to the child; this is called recessive inheritance and includes conditions such as Tay-Sachs disease or cystic fibrosis.

Finally, some boys inherit disorders from genes passed on to them by their mothers. These defects, which include conditions such as hemophilia and color-blindness, are called X-linked because the genes are carried on the X chromosome. Because males have only the one X chromosome they receive from their mothers (females have two X chromosomes — one from each parent), a faulty gene on the X chromosome they receive will be more likely to cause a problem because they don't have a normal copy of the gene on the other X chromosome that females have. Females who have an altered gene on one X chromosome and an intact on the other may have mild features of the X linked condition.

The number or structure of chromosomes also can cause birth defects. An error during the formation of an egg or sperm can cause a baby to be born with too few or too many chromosomes, or with a damaged chromosome. Birth defects caused by chromosome problems include Down syndrome. The risk of this type of birth defect often increases with the age of the mother.

Environmental causes of birth defects have more to do with the mother's health and exposure to chemicals or diseases. When a mother has certain infections (such as rubella) during pregnancy, it can cause birth defects. Alcohol abuse by the mother causes fetal alcohol syndrome, and certain medications taken by the mother can cause birth defects.

Multifactorial birth defects are caused by a combination of genetic and environmental factors and include congenital heart defects, neural tube defects, and cleft lip and palate.

Although you can take steps to prevent birth defects, a birth defect can happen even if you or your partner have no history of birth defects in your families or if you've had healthy children in the past.

Common Birth Defects

Cleft lip and/or palate occurs when the tissues of the mouth or lip don't form properly during fetal development. A cleft lip is a long opening between the upper lip and the nose. A cleft palate is an opening between the roof of the mouth and the nasal cavity.

In the United States, oral clefting occurs in 1 in 700 to 1,000 births, making it one of the most common major birth defects. Clefts occur more frequently in children of Asian, Latino, or Native American descent; it's believed that a variety of environmental and genetic factors cause clefting, but it's unknown exactly which ones. Clefting is a birth defect that can be surgically repaired after birth.

Cerebral palsy usually isn't detected until weeks to months after birth, depending on the severity of the condition. The term actually refers to a group of conditions affecting control of movement and caused by brain damage. People with cerebral palsy have difficulty controlling the motions their muscles make — which muscles and how severely they are impaired varies from person to person.

About 70% of people with cerebral palsy also have other disabilities, most often intellectual disability (mental retardation). Some children with cerebral palsy may have trouble walking; others may not be able to swallow or speak. Cerebral palsy occurs in 2 to 6 of every 1,000 births; about 10,000 children born in the United States each year develop cerebral palsy.

In most cases, the cause of cerebral palsy isn't known, but some are due to prematurity or brain damage during the last trimester of pregnancy or around the time of birth.

Cerebral palsy can also have a genetic cause or may be due to head injuries or meningitis that occur after birth. Therefore, not all cerebral palsy is considered a birth defect. Therapy to improve motor skills, surgery, and braces and other types of equipment and assistive technology can help improve mobility and muscle control. Speech therapy and occupational therapy can help as well.

Clubfoot is a term used to describe a group of structural defects of the foot and ankle in which the bones, joints, muscles, and blood vessels are formed incorrectly. These defects range from mild to severe and may affect one or both feet. Feet affected by this defect most often point down, turn in, and usually have a limited range of motion.

This is a relatively common birth defect, affecting about 1 in 735 babies born each year in the United States. Boys are affected almost twice as often as girls. In most cases the cause is unknown, but some cases of clubfoot happen as a result of a genetic disorder, or problems inside a mother's uterus that can affect or restrict the development of her baby's foot (for example, having too little amniotic fluid). This condition can be treated by applying a cast to the foot immediately after birth. This treatment works the majority of the time; if it doesn't, surgery and further casting are usually required.

Congenital hip dislocation occurs when the round upper end of the thighbone doesn't sit inside the socket of the pelvis properly. This can happen in one or both hips. It happens in about 1 or 2 in 1,000 births, more often in girls, and tends to run in families, although the exact cause is unknown. Usually it is detected at birth and treated immediately by placing the baby in a soft sling for 6 to 9 months. If it's not recognized and treated early, surgery may be necessary.

Congenital hypothyroidism, which occurs in about 1 in 3,000 to 4,000 births, results when the baby's thyroid gland (located in the front of the neck) is absent or underdeveloped at birth or if there is a metabolic defect blocking production of thyroid hormone. This causes the infant to be unable to produce adequate amounts of thyroid hormone, which is important for supporting normal growth and brain development.

Developmental delay and permanent intellectual disability can result if the condition is not recognized and treated (with oral thyroid hormone) within the first few weeks of life. Because of this, every state in the United States and most other countries routinely screen all newborns for the condition with a blood test performed shortly after birth.

Fetal alcohol syndrome (FAS) is characterized by slowed growth, mental retardation, abnormalities in facial features, and problems with the central nervous system. Every year between 2,000 and 12,000 babies in the United States are estimated to be born with defects caused by alcohol. FAS cannot be cured or treated, but can be prevented by avoiding alcohol intake during pregnancy.

Neural tube defects (NTDs) occur in the first month of pregnancy when the structure that develops into the brain and spinal cord is forming. Normally, this structure folds into a tube by the 29th day after conception. When the tube doesn't close completely, the baby has an NTD; many babies with these defects are stillborn or die soon after birth.

The two most common forms of NTDs are:

• Spina bifida, which happens when the spinal column doesn't close completely around the spinal cord. It ranges from mild to severe and can be associated with loss of bladder and bowel function, paralysis, and, in some cases, death.
• Anencephaly, which occurs in 3 out of 10,000 births, involves the lack of development of parts of the brain.

NTDs are multifactorial defects, which according to the March of Dimes occur in about 2,500 babies a year in the United States, or 1 out of every 2,000 live births. Studies have shown that the frequency of these defects may be substantially reduced when the mother gets enough folic acid before and during pregnancy, especially during the first trimester.

Women must make sure to receive enough folic acid before they become pregnant because the neural tube closes about 1 week after the first missed menstrual period — so mothers cannot wait to start folic acid when they first realize they're pregnant. For this reason, it is recommended that women take folic acid throughout their reproductive years.

Defects of the Heart

Heart defects occur when any of the parts of the heart fail to develop properly. They include:

• Atrial and ventricular septal defects, which are holes in the walls that separate the heart into left and right sides.
• Patent ductus arteriosus, which is present when the tubular blood channel that allows the blood to bypass the lungs while the baby is in the womb doesn't close (as expected) after birth.
• Aortic or pulmonary valve stenosis, which are narrowings of the valves that allow blood to flow from the heart to the lungs and other parts of the body.
• Coarctation of the aorta, which is a narrowing of the aorta, the major blood vessel carrying blood from the heart to the rest of the body.
• Transposition of the great arteries, which is the reversal of the connections of the aorta and the pulmonary artery with the heart.
• Hypoplastic left heart system, which is when the side of the heart that pumps blood to the body is underdeveloped or nonexistent.
• Tetralogy of Fallot, which is a combination of four heart defects that involves restriction in the flow of blood to the lungs.

These are among the most common defects, occurring in as many as 1 in 150 births. The specific cause of most heart defects isn't known, although multiple factors may alter the development of the heart during the first 8 to 9 weeks of fetal growth.

Exposure to certain medications (such as the antiseizure drug phenytoin, thalidomide, and chemotherapy drugs) during the first trimester of pregnancy may play a role in causing heart defects. Other causes include maternal alcohol abuse, rubella (German measles) infection, and diabetes during pregnancy.

Defects of the Gastrointestinal Tract

Gastrointestinal defects are structural defects that can occur at any point along the gastrointestinal tract, which is made up of the esophagus, stomach, small and large intestines, rectum, and anus. The incomplete or abnormal development of any of these organs can cause obstructions or blockages that can lead to swallowing difficulties, vomiting, and problems with bowel movements.

Some of these defects are:

• esophageal atresia, or incomplete development of the esophagus
• diaphragmatic hernia, a defect in the layer of muscle separating the chest from the abdomen that allows some of the abdominal organs to protrude up into the chest
• pyloric stenosis, a condition in which the muscular wall of the passage carrying food from the stomach to the small intestine is abnormally thick and the passage narrow, forcing food back out through the esophagus (vomiting)
• Hirschsprung's disease, in which a section of the large intestine is missing the nerves that control its contractions, resulting in severe constipation and sometimes bowel obstruction
• gastroschisis and omphalocele are defects in the abdominal wall allowing the intestine and other abdominal organs to protrude
• anal atresia involves lack of or incomplete development of the anus, causing it to be absent or smaller than it should be, often with the opening in the wrong place
• biliary atresia, in which the bile-carrying ducts in the liver either didn't develop or developed abnormally

The frequencies of these disorders vary, ranging from 1 in 32,000 births to 1 in 10,000 births. Genetics play some role in all these defects, but it is unclear exactly what role or to what degree. Early detection and treatment of these defects is important, as they can lead to serious health problems and even death if left untreated. Surgery is usually necessary to repair these defects.

Genetic Birth Defects

Cystic fibrosis (CF) is a disease mainly affecting the respiratory and digestive systems. An inability to carry chloride (one of the chemicals in table and body salts) from the cells that line organs such as the lungs and pancreas to their outer surfaces causes the body to produce a thick, sticky mucus. Children with CF can have trouble breathing and digesting food; symptoms include chronic respiratory problems and pneumonia, bulky stools, and poor weight gain.

This defect is genetic — 1 in 4 children with two parents who carry an altered form of the gene for CF will get the disease; about 1 in 30 people in the United States carries an altered form of this gene. It affects approximately 30,000 people in the United States, most of them Caucasians. Treatment includes therapy to control infections and maintain lung function and adequate nutrition.

Down syndrome is a group of abnormalities that occur in children who are born with an extra (third) copy of chromosome number 21 in their cells. Children with the syndrome have intellectual disability (mental retardation) and distinctive facial and other physical features; these problems are often accompanied by heart defects and other health problems.

The severity of symptoms varies widely from person to person, with the degree of delay ranging from mild to moderate to severe. Down syndrome is a relatively common birth defect, affecting between 1 in 800 and 1 in 1,000 births. The chances of having a baby with Down syndrome increase dramatically with the age of the mother; a woman who's 35 has a 1 in 350 chance of having a baby with Down syndrome, and a woman who's 45 has a 1 in 30 chance.

Although some of the health problems caused by Down syndrome (such as heart defects) may be treated through medication and surgery, there is no cure.

Fragile X syndrome is characterized by mental impairment, ranging from learning disabilities to mental retardation, autistic behaviors, and attentional problems and hyperactivity. Physical characteristics of children with Fragile X include a long face, large ears, flat feet, and extremely flexible joints, especially fingers.

Boys are affected more often than girls, and are more likely to have substantial intellectual disability rather than milder learning impairment. Both boys and girls are likely to have emotional and behavioral problems. Recent studies suggest that Fragile X affects about 1 in 2,000 males and 1 in 4,000 females of all races and ethnic groups.

Fragile X is a genetic disorder that's passed on by men who carry the abnormality to all of their daughters but none of their sons.

The inheritance of Fragile X syndrome is complex and families with an affected individual need careful counseling from a well-informed doctor or genetic counselor. However, a woman with an affected son has about a 50% chance for each subsequent son to also be affected. Fragile X must be passed through generations in a family before a child is affected. There is no cure for Fragile X, although researchers are exploring ways to prevent it and deal with the complications.

Muscular dystrophy is a general term that's used to describe more than 40 different types of muscle diseases, all of which involve progressive weakness and degeneration of the muscles that control movement. Heart muscles and some other involuntary muscles are also affected in some forms of muscular dystrophy, and a few forms involve other organs as well. Almost all forms of the disorder are genetic and cannot be cured. Treatment includes physical and respiratory therapy, the use of assistive technology, and medications.

Phenylketonuria (PKU) is a metabolic disorder that affects the way the body processes protein; it can cause intellectual disability (mental retardation). A baby born with PKU appears normal, but if the disease isn't treated, the child will suffer from developmental delays that are apparent by the first birthday. About 1 baby in 10,000 to 25,000 in the United States is born with PKU.

This is a genetic disorder. If both parents carry an altered form of the gene, there's a 1 in 4 chance a child will be born with the disorder. In other words, a child will inherit two copies of the altered gene. Fortunately, it is usually detected within a few days after birth by a screening blood test that is routinely performed on infants in the United States and other developed countries. If the child is promptly treated with a special diet, intellectual disability can be prevented.

Sickle cell disease is a disorder of the red blood cells in which an abnormal shape of the cells results in chronic anemia (low blood count), periodic episodes of pain, and other health problems. The disease is genetic; if both parents carry the altered form of the gene, their child has a 1 in 4 chance of having it. In the United States, sickle cell anemia affects mostly African Americans and some Latinos. The disease occurs in about 1 in every 500 African-American births and 1 in every 1,000 to 1,400 Latino-American births.

Treatment for sickle cell disease may include taking antibiotics to prevent infection, blood transfusions, and bone marrow transplantation. Parents can be tested to see if they're carriers of the gene; most U.S. states now routinely perform a screening blood test for the disease on newborns.

Tay-Sachs disease affects the central nervous system, causing blindness, dementia, paralysis, seizures, and deafness; it's usually fatal within the first few years of life. Babies with this disease appear normal when they are born; the symptoms develop during the first few months of life.

It is genetic and occurs most often in Jews of central or eastern European descent or in people of French-Canadian/Cajun ancestry; when two parents are carriers, a child has a 1 in 4 chance of having it. Although there isn't any treatment for this disease, there's a test to help parents determine if they are carriers of the gene.

Infections That Cause Birth Defects

Infections during pregnancy can cause a variety of birth defects. Examples include:

• Congenital rubella (the infection posing the highest risk for fetal damage) syndrome is characterized by vision and/or hearing loss, heart defects, mental retardation, and cerebral palsy. Because of nearly universal immunization congenital rubella is almost never seen.
• Toxoplasmosis infection of the mother can result in eye infections that threaten vision, hearing loss, learning disabilities, enlarged liver or spleen, mental retardation, and cerebral palsy in the infant.
• Genital herpes virus infection of the mother can cause brain damage, cerebral palsy, vision or hearing impairment, and death of the baby if the virus is transmitted to the infant before or during the birth. Herpes complications are most commonly due to infection during the birth process, so are not commonly classified as birth defects.
• Fifth disease can cause a dangerous form of anemia, heart failure, and in some cases fetal death.
• Congenital varicella syndrome, which is caused by chickenpox, can lead to scars, defects of muscle and bone, malformed and paralyzed limbs, a smaller-than-normal head, blindness, seizures, and intellectual disability (mental retardation). This is an uncommon occurrence in pregnant women who become infected with chickenpox.
• Cytomegalovirus (CMV) is a virus that, if contracted by a woman during pregnancy, can lead to low birth weight, intellectual disability (mental retardation) or learning disabilities, and hearing loss.

Talk to your health care provider about ways to avoid these infections while you're pregnant and what you should do if you're exposed to any of them.

Diagnosing Birth Defects

Routine prenatal screening — which includes compiling a thorough medical history, ultrasound testing, and certain blood tests — can do two important things:

1. help determine if the mother has an infection or other condition that is dangerous to the fetus
2. help determine if the fetus has certain birth defects

Defects that may be detected through prenatal screening include:

• neural tube defects (spina bifida, anencephaly)
• Down syndrome
• other chromosome abnormalities
• inherited metabolic disorders
• congenital heart defects
• gastrointestinal and kidney malformations
• cleft lip or palate
• certain birth defects of the limbs
• congenital tumors

It's important to remember that screening identifies only the possibility that a baby has a defect. It's possible to give birth to a healthy baby after a screening test shows that a defect may be present. You aren't required to have any prenatal screening; talk to your doctor about any tests he or she thinks you should have.

Your baby will be tested after birth (with your permission) to screen for certain birth defects that require treatment soon after birth. Exactly what your baby will be tested for varies from state to state (you can ask your health care provider or the hospital nursery which tests your state performs routinely), although all states screen for PKU, congenital hypothyroidism, and about 40 other conditions identified using a technology called tandem mass spectroscopy.

The National Institutes of Health (NIH) recommends that all African-American babies be tested for sickle cell disease; almost all states currently do so.

Other disorders that your state may test newborns for include:

• cystic fibrosis
• congenital adrenal hyperplasia (an inherited disorder of the adrenal gland that can cause severe illness in newborns if not diagnosed and treated within the first few weeks of life)
• hearing loss

If you have a concern about another specific birth defect, you may be able to have your baby tested for it. Talk to your health care provider about this before the baby is born.

Can Birth Defects Be Prevented?

Many birth defects can't be prevented; however, you can take some precautions before and during pregnancy:

Before you get pregnant. Women who are planning to become pregnant should make sure their vaccinations are up to date, that they don't have any sexually transmitted diseases (STDs), and that they get the daily recommended dose of folic acid. One way to ensure this is to start taking prenatal vitamins several months before you begin trying to conceive.

It's generally best to avoid unnecessary medications during pregnancy, so make sure you talk to your doctor about any and all over-the-counter and prescription medicines you're taking before you get pregnant; you'll want to stop taking any that aren't vital to your health. Don't do this without talking to your doctor, however.

If you or your partner have a history of any kind of birth defects in your family, if you've already had a child with a birth defect, or if you are part of a high-risk group (because of your age, ethnic background, or medical history), consider consulting a genetic counselor before you get pregnant. More is being learned about the genes and other factors involved in birth defects all the time and genetic testing and screening are becoming increasingly useful aspects of pre-pregnancy planning and pregnancy. A genetic counselor can give you advice about prenatal testing and help you deal with any concerns or fears you might have.

While you're pregnant. The best thing that pregnant women can do to increase their likelihood of having a healthy baby is to make sure they take care of their bodies during pregnancy by:

• not smoking and avoiding secondhand smoke
• avoiding alcohol
• avoiding all illicit drugs
• eating a healthy diet and taking prenatal vitamins
• getting exercise and plenty of rest
• getting early and regular prenatal care

Talk to your health care provider about other precautions you can take to protect the health of your baby — don't be afraid to ask questions if you're concerned.

Reviewed by: Louis E. Bartoshesky, MD, MPH
Date reviewed: June 2010
Originally reviewed by: Linda Nicholson, MS, MC