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Birth Defects

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Last Edited: 10/7/2010

Types of Birth Defects

A baby may be born with a birth defect caused by a problem in his or her chromosomes, metabolism, formation of external body parts (such as limbs) or internal organs, or all three. On this website, we are only focusing on a limited set of chromosomal and structural defects.  Below is a table that lists the birth defects for which this website has information.  They are categorized by which area of the body is affected by the defect.

 

Area Affected

Chromosome

Face

Brain and Spinal Cord

Reproductive System

Heart

Intestines

Limbs

Name

Down Syndrome (Trisomy 21)

 

Cleft Lip (with or without cleft palate)

Cleft Palate (without cleft lip)

 

Anencephaly

Spina Bifida

 

Hypospadias

Hypoplastic Left Heart Syndrome

Tetralogy of Fallot

Transposition of the Great Arteries

Gastroschisis

 

Upper Limb Deficiencies

Lower Limb Deficiencies

 

 


Chromosomal Defects

Chromosomes are the structures in cells that carry a person’s genetic material, or DNA.  Chromosomal defects can occur in several forms. Infants may be born with too many or too few chromosomes. Chromosomal abnormalities may also occur when parts of chromosomes are broken or rearranged. These defects may happen when an egg or sperm cell is developing.

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Down Syndrome (Trisomy 21)

Down syndrome, also known as Trisomy 21, usually occurs when the egg or sperm divides incorrectly, so that the infant receives an extra copy of chromosome 21.  Individuals with Down syndrome have 47 chromosomes, instead of 46.  Down syndrome affects about 1 in 800 infants per year in the United States (about 3,400 total).

Although the severity of this condition varies from person-to-person, individuals born with Down syndrome tend to have developmental and physical problems including:

  • Characteristic facial features including eyes that slant upward, small ears, small mouth, small nose with flattened nasal bridge
  • Somewhat altered physical appearance including short neck, small hands and feet, low muscle tone, short stature
  • Some form of intellectual disability
  • Congenital heart disease / heart defects
  • Intestinal malformations
  • Vision problems
  • Hearing problems
  • Predisposition to colds, ear infections, and other upper respiratory health conditions
  • Increased risk for childhood leukemias
  • Premature aging, dementia, memory loss, and impaired judgment in adults

Down syndrome is often diagnosed through routine testing during pregnancy.  Pregnant women may choose to have a blood test during the first or second trimester.  This blood test can show an elevated risk that the fetus has Down syndrome, but it cannot definitively diagnose cases.  If the blood test indicates a need for additional testing, women are usually referred to genetic counseling and may be offered one of two tests—amniocentesis or chorionic villus sampling (CVS)—to more accurately diagnose or rule out Down syndrome.

The risk of having an infant with Down syndrome increases with maternal age.  At age 35, the risk is about 1 in 400.  At age 40, the risk is about 1 in 100.  At age 44, the risk is about 1 in 30.

More information and resources can be found on the California Birth Defects Monitoring Program's Down Syndrome Fact Sheet (PDF).  

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Structural Defects

Doctors refer to abnormalities in a newborn’s limbs or internal organs as structural defects.  The structural defects described on this website are defects associated with the:

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Oral-Facial Clefts

Oral-facial clefts occur when the structures that form an infant’s lip and/or mouth do not completely fuse during development. Clefts can range in size and severity. Oral-facial clefts affect about 6,800 infants per year in the United States.

Clefts are divided into two conditions: cleft lip (with or without cleft palate) and cleft palate (without cleft lip).

More information and resources can be found on the California Birth Defects Monitoring Program's Cleft Lip / Cleft Palate Fact Sheet (PDF).  

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Cleft Lip (with or without cleft palate)

  • Cleft lip is opening in upper lip
  • Can be small slit in lip to large opening from lip to nose
  • Cleft palate is opening in roof of mouth.  It does not occur in all cleft lip cases
  • Affects about 4,200 infants per year  in the United States
  • Occurs more often among Asians and Native Americans  
  • Usually surgically repaired 3 months after birth

More information and resources can be found on the California Birth Defects Monitoring Program's Cleft Lip / Cleft Palate Fact Sheet (PDF)

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Cleft Palate (without cleft lip)

  • Cleft palate is opening in roof of mouth
  • Occurs when two sides of palate do not fuse correctly
  • Affects about 2,600 infants per year in the United States
  • Usually repaired between 6 to 18 months after birth 

The causes of oral-facial clefts are not well understood. Genes and environmental factors may impact the prevalence of oral-facial clefts. Research indicates that there may be an elevated risk when a pregnant woman takes certain anti-seizure drugs, smokes, drinks alcohol, or has a folic acid deficiency.  

Surgery can correct many oral-facial clefts and usually occurs within 3 to 18 months after birth.  After surgery, many infants and children may have no further problems. Others may have problems such as:

  • Challenges in feeding
  • Dental problems
  • Increased ear infections
  • Speech problems
  • Some hearing loss

More information and resources can be found on the California Birth Defects Monitoring Program's Cleft Lip / Cleft Palate Fact Sheet (PDF).  

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Neural Tube Defects

The neural tube is a narrow channel along the back of a developing embryo that folds and closes to form the brain and spinal cord.  It closes very early in pregnancy, often before a woman realizes she is pregnant.  When it does not close correctly, an infant is born with a neural tube birth defect. 

The causes of neural tube defects are not fully understood, and both genetic and environmental factors contribute to these defects.  Pregnant women are at risk for having a baby with a neural tube defect if they take certain anti-seizure medications, have poorly managed chronic conditions such as obesity or diabetes, or are deficient in folic acid.  Folic acid, in particular, can help prevent neural tube defects if taken before and during pregnancy.

A woman may be screened for neural tube defects during pregnancy through a prenatal blood test.  If the test indicates an increased risk for a neural tube defect in the fetus, she will be referred for genetic counseling, and detailed ultrasound and/or amniocentesis may rule out or confirm the diagnosis.

More information and resources can be found on the California Birth Defects Monitoring Program's Neural Tube Defects Fact Sheet (PDF), and the Genetic Disease Screening Program's Prenatal Screening website.
 

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Anencephaly

Anencephaly occurs when the portion of neural tube that forms the brain does not close during the first weeks of pregnancy.  Infants with anencephaly lack part of the brain, skull, and scalp.  Anencephaly affects about 1,000 infants per year in the United States.

Infants born with anencephaly do not have enough upper brain function to survive.  All infants born with anencephaly die within the first few hours or days of life.   

More information and resources can be found on the California Birth Defects Monitoring Program's Anencephaly Fact Sheet (PDF).  

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Spina Bifida

Spina bifida occurs when the portion of the neural tube that forms the spinal cord does not close completely during weeks 3 and 4 of pregnancy.  It is one of the most common birth defects in the United States, affecting about 1,500 infants per year.

There are three forms of spina bifida: occulta, meningocele, and myelomeningocele.
 

  • Occulta

Occulta is the mildest form of spina bifida.  It results when there is a small defect or gap in a few of the vertebrate that make up the spine.  In this form of spina bifida, the spinal cord and nerves are usually normal, and there is no opening on the back.   

Occulta is relatively harmless.  It can be so mild that spinal function is not affected.  At birth, motor or sensory impairments may not be evident.  Later in childhood or adulthood, subtle and progressive neurologic deterioration often becomes evident.  Occulta can be diagnosed at any age.    

  • Meningocele

Meningocele is the rarest form of spina bifida.  It results when a cyst or fluid filled sac pokes through the open part of the spine.  This sac contains membranes that protect the spinal cord, but does not contain spinal nerves.  Infants born with meningocele spina bifida usually need surgery to remove the sac and usually develop normally. 

  • Myelomeningocele

Myelomeningocele is the most common and the most severe form of spina bifida.  It results when infants are born with a cyst that contains membranes and tissue from the spinal cord itself.  Myelomeningocele may also take the form of a fully exposed section of spinal cord and nerves without a cyst.  Infants born with this type of spina bifida are at high risk for infection until the exposed spinal area is surgically closed.

Surgery is usually required within 24 to 48 hours after birth.  Infants with myelomeningocele spina bifida are often partially paralyzed, require a wheelchair or other mobility aid, and tend to have bladder and bowel control problems.  The severity of paralysis depends largely on the location of the cyst and will be more severe the higher its location on the spine.

Infants born with spina bifida are at higher than usual risk for accumulating excess fluid inside the brain (hydrocephalus).  This condition affects 70 to 90 percent of children with myelomeningocele.  If untreated, pressure from excess fluid inside the brain can cause brain damage.  In order to treat this, a shunt is surgically inserted to drain the excess fluid. 

Infants diagnosed with spina bifida, and particularly myelomeningocele, are at some risk for future learning disabilities.  They may also have a tethered spinal cord, meaning that the spinal cord is held in place by surrounding tissue, which can become a problem as the child grows in size.  This may require further surgery.  

More information and resources can be found on the California Birth Defects Monitoring Program's Spina Bifida Fact Sheet (PDF).  

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Reproductive System

Hypospadias

This birth defect occurs in males when the opening of the urethra, the tube that carries urine from the bladder to the outside of the body, is located along the underside of the penis instead of at the tip.  This defect occurs when urethra does not complete its development during the pregnancy.

The exact cause of hypospadias is unknown.  However, research indicates that prenatal exposure to hormones such as progesterone and estrogen may increase the risk of hypospadias. 

The severity of this birth defect varies by location of the hypospadias.  In mild cases, the problem is cosmetic rather than causing any functional problem after birth.  When desired, surgery is usually performed when the infant is between 6 to 18 months old.

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Heart Defects

Heart defects are among the most common birth defects and are the leading cause of birth defect related deaths.  They may occur along with chromosomal birth defects such as Down Syndrome and Turner Syndrome.  Heart defects affect about 35,000 infants per year in the United States.

Heart defects develop in the early weeks of pregnancy when the heart is forming.  Heart defects may be detected prenatally using ultrasound (echocardiography), and medications might be prescribed to restore a normal heart rhythm.

However, most heart defects are usually diagnosed after birth by chest x-ray, electrocardiogram, and echocardiogram.  A heart abnormality seldom causes problems while the fetus is in the womb and may only become evident after birth.  Most infants diagnosed with major heart abnormalities undergo surgery within the first few months of life.  Small holes in the heart usually close without treatment.

Although the causes of most congenital heart defects are unknown, there are several environmental factors that may contribute to their occurrence.  Prenatal risk factors include:

  • Exposure to rubella (German measles), influenza, and other infections
  • Alcohol use
  • Cocaine use
  • Medications such as isotretinoin (Accutane) and some anti-seizure medications
  • Exposure to chemical solvents such paint, varnish, and some cleaning products

More information and resources can be found on the California Birth Defects Monitoring Program's Heart Defects Fact Sheet (PDF)

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Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome is a term for a group of defects, indicating that the left side of heart is underdeveloped.  In this condition, the left ventricle is too small to support life.  If the infant does not undergo surgery, this birth defect is fatal in the first few days or weeks of life.

More information and resources can be found on the California Birth Defects Monitoring Program's Heart Defects Fact Sheet (PDF)

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Tetralogy of Fallot

Tetralogy of Fallot affects the flow of blood through the heart.  Although present at birth, symptoms may not appear until months later.  It is a combination of four defects that tend to occur together.  These include:

  • A hole in the wall between the ventricles (ventricular septal defect)
  • Narrowing of the artery that carries blood from heart to the lungs (pulmonary stenosis)
  • An aorta that grows from both ventricles rather than from the left one only
  • A thickened muscular wall of the right ventricle (right ventricular hypertrophy)

In addition to general congenital heart defect risk factors, risk factors for tetralogy of Fallot include poor prenatal nutrition and older maternal age.  Infants with tetralogy of Fallot may show poor growth, and they may have episodes in which some or all of their skin appears blue-ish (“cyanosis”).  This defect is usually repaired in the first few months of life.

More information and resources can be found on the California Birth Defects Monitoring Program's Heart Defects Fact Sheet (PDF)

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Transposition of the Great Arteries (Vessels)

Present at birth, transposition of the great arteries occurs when the two main arteries carrying blood away from the heart (the pulmonary artery and the aorta) are switched or transposed in position.  These children will have other structural heart abnormalities along with the transposition.  They may be extremely sick, and their heart problems will require corrective surgery.

More information and resources can be found on the California Birth Defects Monitoring Program's Heart Defects Fact Sheet (PDF)

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Intestines

Gastroschisis

Gastroschisis is a birth defect that occurs when a portion of the infant’s intestines protrudes through the body, typically just next to the umbilical cord.  This defect can range in severity and size, and it can affect other organs such as the liver.  About 1,500 infants in the United States are born per year with this defect.  Surgical correction is required.

The causes of gastrochisis are still unknown.  Some research has shown that adolescent mothers or mothers who consume a high fat and high cholesterol diet may be more likely to give birth to an infant with gastrochisis.

Infants and children who have had gastrochisis may face challenges moving digested food through the stomach and intestines and absorbing nutrients.

More information and resources can be found on the California Birth Defects Monitoring Program's Gastroschisis Fact Sheet (PDF)

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Limb Deficiencies 

Affecting about 1,500 infants per year in the United States, a limb deficiency occurs when a part of one or both arms or legs fails to form completely during pregnancy.  The resulting limb is reduced from its normal size or is missing.  This condition is also known as a limb reduction defect.

The causes of limb deficiencies are not well understood.  Research suggests that some exposures during pregnancy may increase the risk of having an infant with a limb reduction defect.  Exposures that are being considered by researchers as potentially contributing to these defects include viruses, chemicals, medications, and tobacco smoke.

The severity of this birth defect depends on the location and size of the limb reduction.  Infants born with upper and/or lower limb deficiencies may face challenges with:

  • Motor skill development
  • Caring for oneself
  • Physical activity
  • Social and emotional issues

Treatment for limb deficiencies varies.  Potential treatments can include prosthetics (artificial limbs), orthotics (splints or braces), surgery, and/or rehabilitation (physical and occupational therapy). 

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Upper Limb Deficiencies

Also known as an upper limb reduction, this defect occurs when part of the fetal arm or hand (upper limb) does not form completely during pregnancy.

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Lower Limb Deficiencies

Also known as a lower limb reduction, this defect occurs when part of the fetal leg or foot (lower limb) does not form completely during pregnancy.

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