A birth defect is any abnormality present at birth that results in physical or mental disability or death. The abnormality may affect the child’s structure, ability to function or metabolism. According to the Centers for Disease Control and Prevention (CDC), about 3 percent of infants born in the United States (about one in every 33 births each year) have some kind of birth defect. Furthermore, birth defects are the leading cause of death in the first year of life.

According to the American Academy of Family Physicians (AAFP), there are more than 4,000 different birth defects. They vary widely, from structural defects (e.g., heart defects, neural tube defects) to metabolic problems (e.g., phenylketonuria) and combinations of both. Many birth defects are genetic disorders caused by alterations to genes or chromosomes that affect normal development (e.g., Down syndrome, sickle cell anemia, cystic fibrosis).

Some birth defects are caused by a single, well-documented factor, such as a missing or abnormal gene or chromosome. Many are caused by a combination of several factors, such as maternal age, smoking, or medication use. Substances or infections that affect a pregnant woman may also affect the developing fetus and cause birth defects.

Many birth defects are defined by their cause, including fetal alcohol syndrome (due to maternal alcohol consumption) and congenital rubella syndrome (due to an infection with rubella in the first trimester). However, the causes of most birth defects are not known.

Birth defects are often detected before birth. Defects that have not been prenatally detected and are not obvious when the infant is born are usually discovered through newborn screening tests. While most birth defects are discovered in infancy, within the first year of life, some others may not be detected until childhood or even adulthood.

Some birth defects require little treatment. Other defects cannot be treated or will result in early death regardless of treatment attempts. However, most birth defects lie somewhere between these two extremes and are treatable to some degree.

Many birth defects are corrected through surgery in early infancy. Others can be treated through nonsurgical means. Birth defects that cause mental retardation and other developmental disabilities can present lifelong challenges to both parents and children. A few birth defects can be treated before birth using injections or even prenatal surgery.

A birth defect is any disabling or fatal abnormality in structure, function or metabolism that is present at birth. The disability may be physical or mental. The medical community has identified several thousand different birth defects. Some are very minor, while others are severe or life-threatening.

Birth defects are the most common cause of infant death during the first year of life. According to the Centers for Disease Control and Prevention (CDC), more than 20 percent of all infant deaths occur due to birth defects. Those infants with moderate to severe birth defects who survive are more likely to be sick or have long-term problems than other infants. However, proper treatment often allows many children born with birth defects to lead full, healthy lives.

Pregnancy is an incredibly complex process. A single fertilized egg grows and divides into billions of cells and many different body systems, eventually forming a baby. Any change that affects that process, to any cell, gene or enzyme, can result in an anomaly. Many anomalies that occur during pregnancy are severe enough that they are incompatible with life and a miscarriage occurs. In other cases, the baby continues to develop but is born with a birth defect.

A birth defect can develop at any stage of pregnancy. However, most birth defects occur during the first three months of pregnancy, which is the most important stage of development due to the formation of the organs (e.g., the brain, spinal cord). Any developmental abnormalities that occur during these early stages of development can cause the fetus to grow defectively for the rest of the pregnancy. Any factor that interrupts the proper formation of the organs can result in a birth defect.

According to the American Academy of Family Physicians (AAFP), there are more than 4,000 different birth defects, which can be classified in numerous ways. They vary widely, from structural defects (e.g., heart defects) to functional problems (e.g., blindness, deafness) to metabolic problems, where the body lacks or cannot process certain enzymes. Some birth defects may encompass one or more problems.

Birth defects may also be classified by their suspected cause, which may also vary. For example, many birth defects are genetic disorders that occur due to a problem present in the infant’s genetic structure and may also include structural, functional or metabolic disorders or any combination of the three.   

Some of the most common birth defects include:

• Heart defects. The most common structural birth defects. According to the March of Dimes, about one of every 100 to 200 infants is born with a heart defect. They can range in severity from mild to serious and may include holes in the heart or malformed heart chambers or valves. Many can be effectively treated using surgery or other means. Heart defects cause more infant deaths than any other birth defect.
  
  
• Genital or urinary defects. According to the March of Dimes, around one in every 135 infants is born with a defect in his or her genital or urinary system. These birth defects range from mild to severe. One example is hypospadias, which may affect male infants. In infants with this defect, the urethral opening occurs on the underside of the penis instead of the tip. It can be corrected through surgery.
  
  
• Cleft lip and/or palate (Orofacial clefts). According to the Centers for Disease Control and Prevention (CDC), around one in every 700 to 1,000 infants is born with an orofacial cleft. The disorder is more common among Asian, Hispanic and Native American infants. It can be repaired surgically.
  
  
• Clubfoot. The incorrect formation of the bones, joints, muscles and blood vessels in the foot and ankle. It causes the feet to point down and turn in and usually limits the range of motion of the feet. According to the AAFP, clubfoot occurs in about one in every 735 infants in the United States each year. Treatment may involve casts and surgery.
  
  
• Down syndrome. Among the most common genetic disorders. Down syndrome is caused by an extra chromosome and is characterized by slow growth, mental retardation and abnormal facial features. According to the CDC, Down syndrome occurs in around one in every 800 infants. It is more common in infants born to older mothers.
  
  
• Congenital hip dislocation. Occurs when the round upper end of the thighbone fails to sit properly inside the socket of the pelvis. This can happen in one or both hips and tends to affect girls more than boys. It usually is detected at birth and is treated by placing the infant in a soft sling for six to nine months.
  
  
• Congenital hypothyroidism. Occurs when an infant’s thyroid gland is absent or underdeveloped at birth. This prevents the child from producing enough thyroid hormone, a substance which supports normal growth and brain development. If not treated right away, this condition can lead to developmental delays and permanent retardation. To prevent this, infants are routinely given a blood test shortly after birth to check for congenital hyperthyroidism.
  
  
• Cerebral palsy. A group of disorders that cause brain damage and affect muscle control. The degree of impairment varies greatly among patients. According to the AAFP, between two and six of every 1,000 infants in the United States (about 10,000 infants each year) are born with cerebral palsy. Mental retardation and other disabilities also occur in around 70 percent of patients with the condition, the AAFP reports.
  
  
• Neural tube defects. Defects in the brain or spinal cord that occur in the first month of pregnancy. According to the CDC, they appear in around one in every 1,000 pregnancies. The most common neural tube defects include:
  
  
• • Spina bifida. The most common neural tube defect. This defect occurs when the vertebral column fails to close completely, leaving the spinal cord partially exposed. According to the March of Dimes, about one in every 2,000 infants is born with spina bifida. This defect can often be repaired surgically. Some children with spina bifida experience few problems, while others have some paralysis and other nerve problems.
    
    
  • Anencephaly. A neural tube defect that occurs when parts of the brain fail to develop. Infants born with this condition die at birth or shortly after. According to the AAFP, it affects about three in every 10,000 infants.
    
    
• Sickle cell anemia. A genetic blood disorder characterized by an abnormal shape of the red blood cells. The condition typically results in chronic anemia, painful attacks and other health problems. According to the AAFP, about one in every 500 African American infants and around one in every 1,000 to 1,400 Hispanic infants are born with this condition.
  
  
• Cystic fibrosis. A condition most common in Caucasians. Results in thick mucus in the lungs and other organs, causing breathing and other problems. The American Academy of Pediatrics (AAP) states that about one of every 1,600 Caucasian infants is born with the disease. It is much rarer in African Americans, affecting one in every 17,000 infants, according to the AAP.
  
  
• Tay-Sachs disease. A degenerative metabolic and genetic condition most common in people of European Jewish descent. This disease causes brain damage and often leads to blindness, seizures, dementia and paralysis. It is eventually fatal.
  
  
• Turner syndrome. Occurs when one of the two X chromosomes normally found in females is missing or incomplete. It does not affect males. Common symptoms include short stature and absent or delayed puberty.
  
  
• Fragile X syndrome. A condition characterized by mental impairment, autistic-like behaviors, hyperactivity and attention problems. According to the AAFP, it occurs in about one in every 2,000 male infants and around one in every 4,000 female infants.
  
  
• Gastrointestinal defects. Birth defects that may occur in the digestive tract. They often cause obstructions or blockages and typically require surgical treatment. An example of a gastrointestinal defect is imperforate anus, in which the opening at the end of the digestive tract is missing or closed.

Other genetic disorders include the bleeding disorder hemophilia, achondroplasia (the most common form of dwarfism) and muscular dystrophy. Many genetic disorders include metabolic abnormalities. These birth defects are characterized by an inability to produce, use, or transport a body chemical (e.g., enzyme, protein). Around one in every 3,500 infants is born with metabolic abnormalities, according to the March of Dimes. One example of a metabolic abnormality is phenylketonuria (PKU), in which protein is not properly processed and builds up in the blood and tissue. It leads to mental retardation if left untreated, but early treatment with a special diet that is low in phenylalanine (an essential amino acid) can be used to prevent brain damage.

Many birth defects or groups of birth defects that tend to occur together (syndromes) are defined by their cause. Some of these include:

• Fetal alcohol syndrome. May occur in an infant whose mother consumed alcohol during pregnancy, especially in early pregnancy. Features include mental retardation, problems in the central nervous system (CNS), and abnormalities of the facial features. According the March of Dimes, about one out of every 1,000 infants is born with fetal alcohol syndrome.
  
  
• Rhesus (Rh) disease of the newborn. Occurs when the mother’s blood is incompatible with the blood of the fetus. Features include jaundice, anemia and brain damage. If not treated, this condition can result in the death of the infant. Treatment involves injections of a special blood product (immunoglobulin-Rhogam) at 28 weeks into pregnancy and after the delivery of the infant. About 4,000 infants are born each year with this condition, according to the March of Dimes.

Some birth defects are caused by a single, well-documented factor, such as a missing or abnormal gene or chromosome. Many are caused by a combination of several factors. However, the causes of 70 percent of all birth defects are not known, according to the Centers for Disease Control and Prevention (CDC).

Many birth defects are the direct result of genetic disorders. These are often chromosomal conditions, such as an absent or extra chromosome. Even a single abnormal gene can cause a birth defect. In normal development, a baby receives half of its genes from the mother and half from the father. Genes may be dominant or recessive. For example, if one parent has the recessive gene for the enzyme associated with phenylketonuria (PKU) and the other parent has a dominant gene for the PKU enzyme, the baby will have functioning enzymes and will not develop PKU. Many genetic disorders such as PKU can occur only when both parents contribute a recessive gene, leading to expression of the defect.

Genetic birth defects can also result from a spontaneous mutation in a gene or during embryonic development. Some genes only increase an infant’s risk of a birth defect. These can be passed down for many generations before the defect actually occurs.

Other known causes of birth defects involve environmental factors affecting the fetus and the mother. These environmental factors may be divided into categories such as:

• Teratogens. Any harmful substances that the mother takes in and that pass through the placenta into the fetal bloodstream. Among the best known teratogens is alcohol, which causes fetal alcohol syndrome in about one out of every 1,000 infants, according to the March of Dimes. Maternal smoking has been linked to many birth defects, including cleft lip and palate, heart defects, clubfoot and other limb defects. Recreational drugs are also dangerous to the fetus. The March of Dimes reports that infants whose mothers used cocaine in early pregnancy are five times more likely to have urinary tract defects and damage to the central nervous system. Exposure to certain toxic chemicals, especially solvents (chemicals used in paints, varnishes, lacquers, adhesives, glues and degreasing/cleaning agents), during pregnancy also may increase a woman’s risk of miscarriage or having a baby with birth defects. In addition, a recent study found that men who are exposed to solvents on a regular basis may be at greater risk of fathering offspring with birth defects and low birth weight.
  
  
• Medications. Many medications including those used for treating blood pressure disorders, epilepsy and mental illnesses (e.g., depression) have also been linked to birth defects. However, while women are encouraged to avoid alcohol, nicotine and recreational drugs while pregnant, they may not be able to avoid all medications. All women who are or may be pregnant should discuss all of their medications, including over-the-counter medications, with their doctor.
  
  
• Infections and illnesses. Women with diabetes or high blood pressure have an increased risk of having a child with a birth defect, particularly if these conditions are not under control during the pregnancy. Infections during pregnancy may also lead to birth defects. Rubella carries the highest risk, although it is much less common now that the rubella vaccination is available. According to the March of Dimes, infants have a 25 percent chance of displaying at least one feature of congenital rubella syndrome if the mother is infected during the first trimester of pregnancy. Other infections that may result in birth defects include cytomegalovirus, toxoplasmosis and chickenpox. Sexually transmitted diseases (e.g., syphilis, genital herpes) may also lead to birth defects.
  
  
• Maternal nutrition. Infants born to women who are particularly stressed, obese, or malnourished also have an increased risk of birth defects, particularly neural tube defects. Many neural tube defects are linked to a deficiency in the B vitamin folic acid before and during pregnancy.

In addition to the known causes, some maternal risk factors increase the likelihood of birth defects. These include:

• Age. Infants born to teenagers and women over age 35 have a higher risk of birth defects, particularly chromosomal defects (e.g., Down syndrome). The father’s age may also play a role in the occurrence of birth defects. According to a new study, the genetic quality of sperm gradually deteriorates as men get older, increasing a man’s risk of infertility, fathering unsuccessful pregnancies (miscarriages) and passing along some genetic defects to his offspring (e.g., dwarfism). Another study also found that men who undergo surgery to reverse a vasectomy (procedure that permanently sterilizes a man and takes away his ability to impregnate a woman) may be at greater risk of having genetically defective sperm, which can increase the likelihood of birth defects in their offspring.
  
  
• Pregnancy history. Women with a history of miscarriage or who have had previous children with birth defects also have a higher risk of having another child with a birth defect.
  
  
• Premature birth. Infants born prematurely have a greater risk of having some birth defects, such as cerebral palsy.
  
  
• Multiple pregnancies. Infants in multiple pregnancies, especially higher order multiple pregnancies (three or more babies) are more likely to have birth defects.

There are thousands of birth defects, each with its own unique signs and symptoms. Defects can affect nearly any part of the body, and generally have an effect on the body’s structure, function or metabolism. They may occur alone or in groups. Some birth defects are obvious immediately after birth, while others may not be discovered until later childhood or even adulthood. Some may not demonstrate any signs or symptoms, or may not show signs or symptoms until childhood or adulthood. Because of the wide range of birth defects, nearly any problem (e.g., poor feeding, nonresponsiveness, irritability) could potentially be a sign or symptom of a birth defect. Some other common signs and symptoms of birth defects include:

• Abnormal physical structure. Structural defects result in abnormal physical properties. These may be external, such as misshapen ears or too many fingers or toes. They may be internal, such as with missing or malformed organs. Many structural defects may be obvious both internally and externally, such as with defects in the skull that cause an abnormal shape of the head or face. Musculoskeletal problems or paralysis may be less apparent before a child learns to crawl.
  
  
• Mental impairment. Many birth defects result in learning disabilities or mental retardation. These defects may not become apparent until an infant gets older and appears to be missing developmental milestones associated with a given age. Learning disabilities may not be noticed until a child is 4 or 5 years old.
  
  
• Sensory impairment. Blindness and/or deafness may occur due to a birth defect. This may be due to structural defects in the eyes and/or ears or problems with the central nervous system.
  
  
• Irregular heart rhythms. Murmurs and irregular heart rhythms may be caused by heart defects.
  
  
• Hormone or enzyme deficiencies. Many birth defects result in hormone or enzyme deficiencies. Many of these may be detected in blood, urine or fecal tests. Some enzyme disorders may not be detected until much later, when the child suffers some sort of attack or experiences mental retardation because of malfunctioning enzymes.

Many birth defects can be detected before birth. According to the American Academy of Family Physicians (AAFP), around 250 birth defects can be diagnosed prenatally.  Some are obvious when the infant is born or are discovered through newborn screening tests. Most birth defects are discovered in infancy, within the first year of life. Others may not be detected until childhood or even adulthood.

Prenatal screening tests are used to determine the chance that a particular fetus has a birth defect. They are safe, noninvasive and typically painless. They are not exact, but may be used to determine if prenatal diagnostic tests are necessary. Screening tests may be more accurate when performed earlier in the pregnancy. Some women may not wish to undergo prenatal screening. However, others find that these tests can give them peace of mind or time to prepare for a child with special needs.

Prenatal screening tests include:

• Maternal blood tests. Identify and measure substances in the mother’s blood that reveal information about her fetus. There are a number of these tests available, including the triple screen test and alpha fetoprotein plus, which detect different substances.
  
  
• Detailed ultrasound. Uses sound waves to create an image of the inside of a mother’s womb. This can be used to identify the physical features associated with some birth defects. Ultrasound is particularly useful in the diagnosis of structural defects affecting areas such as the heart and spinal cord.

If screening tests indicate a potential problem, a physician may recommend a diagnostic test. Prenatal diagnostic tests are around 99 percent accurate in identifying Down syndrome and other chromosomal conditions, according to the AAFP. The diagnosis of many other birth defects may not be as accurate. These tests are associated with complications, including a risk of miscarriage and preterm labor. They are typically only recommended for women with a high risk of having a child with a birth defect, including those over the age of 35 years, those with a family history of birth defects or genetic problems, and those who have had abnormal results on screening tests. Parents may use the results of diagnostic tests to prepare for the birth of a special needs child or to consider terminating the pregnancy.

Prenatal diagnostic tests include:

• Amniocentesis. With the aid of continuous ultrasound guidance, a needle is inserted through the abdomen and into the uterus. Then, a small amount of amniotic fluid (the fluid in the uterus) is removed for testing. This test is generally performed between 16 and 20 weeks into the pregnancy.
  
  
• Chorionic villus sampling (CVS). A sample of the placenta is removed for testing. It may be obtained using either a needle through the abdomen (as in amniocentesis) or a tube inserted through the vagina. This test can be performed between eight and 12 weeks of pregnancy.
  
  
• Percutaneous umbilical blood sampling (PUBS). A needle is used to remove a sample of blood from the fetus’ umbilical cord. This test carries higher risks of complications than amniocentesis or CVS and is typically used only when diagnosis must be made very quickly. It is typically performed late in pregnancy, after 20 weeks.

After an infant is born, newborn screening tests are typically performed. These tests are used to detect metabolic disorders, often called inborn errors of metabolism (IEMs), that are not otherwise apparent at birth. They typically require a small sample of blood be taken from the infant’s heel.

Birth defects range from mild to very serious. Some require little treatment at all and some cannot be treated or will result in early death regardless of treatment attempts. However, most birth defects lie somewhere between these two extremes and are treatable to some degree.

Specialists may be helpful or necessary for the treatment of certain birth defects. For example, skeletal defects may require the expertise of a pediatric orthopedist and neural tube defects typically require assistance from a pediatric neurologist and a surgeon.

Some birth defects can be treated before birth. For example, injections of blood products (immunoglobulin-Rhogam) are used to treat Rh disease of the newborn. Heart medications may be given to women carrying infants with certain heart defects and extra vitamins may be taken by women carrying infants with enzyme deficiencies. In some cases, birth defects may even be treated using surgery before birth. Prenatal surgery has been used to repair urinary tract blockages, lung tumors, neural tube defects (e.g., spina bifida) and congenital diaphragmatic hernia (an opening in the muscle between the chest and abdomen). However, these surgeries remain experimental and require further research.

Many structural defects are corrected through surgery in early infancy. Such surgery is often effective enough that the defect is completely cured, as is the case with many heart defects. Many birth defects can also be treated through nonsurgical means. Medications are often quite useful for metabolic defects, for example. Physical and occupational therapy may help infants with birth defects to overcome or correct some defects and build and maintain muscle tone and coordination. Speech therapy may also be useful for some individuals.

Early intervention services can help children with many problems associated with birth defects. These may include feeding support and nutritional services. It usually includes information on assistive technology (e.g., leg braces) and social work services that may help accommodate a child living with birth defects as he or she ages.

Some birth defects are easily preventable. For example, fetal alcohol syndrome can be prevented by avoiding alcohol during pregnancy. However, not all birth defects can be prevented. Healthy parents who do everything their physicians recommend can still have an infant with a birth defect. Many birth defects occur before most women discover that they are pregnant. Women may unknowingly expose their fetuses to conditions that they would otherwise avoid (e.g., drinking alcohol, smoking) if they only realized that they were pregnant.

Pregnancies that are planned have a reduced risk of birth defects. Genetic counseling is common during pregnancy planning. Here, a genetic counselor discusses an individual couple’s chances of having a child with a birth defect. This can help establish realistic expectations. In addition, couples who are carriers of known serious genetic conditions may want to use methods of assistive reproductive technology to minimize the risk of a fetus that will develop a serious or fatal birth defect.

Women who plan their pregnancies tend to take care of themselves as though they were pregnant. This is particularly beneficial because many steps to prevent birth defects are best initiated before conception. For example, taking 400 micrograms of folic acid (a type of B vitamin) daily has been shown to reduce the risk of neural tube defects by 70 percent, according to the American Academy of Family Physicians (AAFP). However, it must be taken both before and during pregnancy. Planning a pregnancy also allows women to treat or control any conditions (e.g., obesity, diabetes, seizures, high blood pressure, thyroid disorders) before their pregnancy.

During pregnancy, there are many things a woman can do to reduce the chance that her child will be born with a birth defect. A healthy diet with plenty of calories, vitamins and nutrients is essential. Plenty of rest and moderate exercise can also help. A woman should discuss how much exercise she needs with a physician. Pregnant women need to avoid smoking (including second-hand smoke), alcohol and recreational drugs. Other substances to be avoided include radiation (e.g., x-rays) and cat litter, which may carry the toxoplasmosis protozoa. Women who are pregnant should also discuss all medications (including over-the-counter medications) and vaccinations with a physician, preferably an obstetrician/gynecologist (Ob/Gyn), who knows about their pregnancy. It is also important for a woman to review recent medications and vaccinations with a physician immediately after finding out about her pregnancy. 

Preparing questions in advance can help patients and parents to have more meaningful discussions with their physicians regarding their or their child’s treatment options. The following questions related to birth defects may be helpful:

1. How high is my risk of having a child (or another child) with a birth defect?
   
   
2. What kind of birth defect does my child have?
   
   
3. How severe is my child’s birth defect?
   
   
4. What may have caused my child’s birth defect?
   
   
5. Can prenatal diagnostic tests indicate the severity of a birth defect?
   
   
6. How may my child’s birth defect affect his/her physical, mental and emotional development?
   
   
7. Can my child’s birth defect be treated?
   
   
8. Could physical, occupational or speech therapy help my child?
   
   
9. How may my child’s birth defect affect his/her schooling?
   
   
10. Could my child’s birth defect cause other problems later in life?
    
    
11. How can I reduce my chances of having another child with this or a similar birth defect in the future?