Spina bifida

Spina bifida

Spina bifida is a birth defect that affects the lower back and, sometimes, the spinal cord. It is one of the most common birth defects in the United States, affecting about 1,500 babies each year (1).Spina bifida is the most common of a group of birth defects called neural tube defects (NTDs). The neural tube is the embryonic structure that develops into the brain and spinal cord. The neural tube normally folds inward and closes by the 28th day after conception. When it fails to close completely, defects of the spinal cord and vertebrae (small bones of the spine) can result.

How does spina bifida affect a child?
There are three forms of spina bifida:

  1. Occulta: In this mildest form, there are usually no symptoms. Affected individuals have a small defect or gap in one or more of the vertebrae of the spine. A few have a dimple, hairy patch, dark spot or swelling over the affected area. The spinal cord and nerves usually are normal, and most affected individuals need no treatment.
  2. Meningocele: In this rarest form, a cyst or fluid-filled sac pokes through the open part of the spine. The sac contains the membranes that protect the spinal cord, but not the spinal nerves. The cyst is removed by surgery, usually allowing for normal development.
  3. Myelomeningocele: In this most severe form, the cyst holds both the membranes and nerve roots of the spinal cord and, often, the cord itself. Or there may be a fully exposed section of the spinal cord and nerves without a cyst. Affected babies are at high risk of infection until the back is closed surgically, although antibiotic treatment may offer temporary protection. In spite of surgery, affected babies have some degree of leg paralysis and bladder- and bowel-control problems. In general, the higher the cyst on the back, the more severe the paralysis.

What causes spina bifida?
The causes of spina bifida are not completely understood. Scientists believe that both genetic and environmental factors act together to cause this and other NTDs. However, 95 percent of babies with spina bifida and other NTDs are born to parents with no family history of these disorders (2).

Who is at risk of having a baby with spina bifida?
Anyone can have a baby with spina bifida. However, couples who have already had a baby with spina bifida or another NTD have an increased risk of having another affected baby. A couple with one child with spina bifida usually has about a 4 percent chance of having another affected baby, and a couple with two affected children has about a 10 percent chance of having another affected baby (2). Similarly, when one parent has spina bifida, there is about a 4 percent chance of passing the disorder on to the baby (2). Couples who have had an affected baby or have a family history of NTDs should consult a genetic counselor to discuss risks to their future children.

In most cases, spina bifida occurs by itself. However, sometimes spina bifida occurs as part of a syndrome with other birth defects. In these cases, recurrence risks in another pregnancy may vary widely.

Women with certain health conditions are at increased risk of having a baby with spina bifida. These conditions include (2,3):

  • Obesity
  • Poorly controlled diabetes
  • Treatment with certain anti-seizure medications

Women with these conditions should consult their health care provider before pregnancy about steps they can take to reduce their risk of having a baby with spina bifida. For example, they can achieve a healthy weight before pregnancy, control their diabetes, change anti-seizure medications and take folic acid (see below).

Spina bifida and other NTDs occur more commonly in some ethnic groups than others. For example, NTDs are more common in Hispanics and Caucasians, and less common among Ashkenazi Jews, most Asian ethnic groups and African-Americans (2).

How is spina bifida treated?

  • Occulta: This condition usually requires no treatment. Most individuals don’t know they are affected, unless the defect is diagnosed during an X-ray for some other reason. Occasionally newborns are diagnosed with this form of spina bifida if they have a dimple or other marking on their back. In some cases, these babies may need to be evaluated for spinal cord abnormalities that could eventually result in complications, such as weakness or numbness in the legs and bladder problems. Occasionally surgery is recommended to prevent these problems.
  • Meningocele: This defect is repaired surgically, and affected babies usually have no paralysis.
  • Myelomeningocele: This form of spina bifida usually requires surgery within 24 to 48 hours after birth (2). Doctors surgically tuck the exposed nerves and spinal cord back inside the spinal canal and cover them with muscle and skin. Prompt surgery helps prevent additional nerve damage and infection. However, nerve damage that already has occurred cannot be reversed. Soon after surgery, a physical therapist teaches parents how to exercise their baby’s legs and feet to prepare for walking with leg braces and crutches. Many children with a defect in the lower spine can walk with or without these devices, although most children with a defect high in the spine require a wheelchair.

What medical problems occur with spina bifida?
Common medical problems include:

    • Hydrocephalus: About 70 to 90 percent of children with myelomeningocele develop hydrocephalus, a build-up of fluid in and around the brain(4). Cerebrospinal fluid cushions and protects the brain and spinal cord. When the fluid is unable to circulate normally, it collects in and around the brain, causing the head to be enlarged. Without treatment, hydrocephalus can cause brain damage and intellectual disabilities.Doctors usually treat hydrocephalus by surgically inserting a tube called a shunt that drains the excess fluid. The shunt runs under the skin into the chest or abdomen, and the fluid passes harmlessly into the child’s body. A newer surgical procedure called endoscopic third ventriculostomy creates a new pathway for draining cerebrospinal fluid. This procedure may be recommended for some children older than 6 months, including some who experience shunt malfunctions(5).
    • Chiari II malformation: Nearly all children with myelomeningocele have an abnormal change in the position of the brain. The lower part of the brain is located farther down than normal and is partly displaced into the upper part of the spinal canal. This can block the flow of cerebrospinal fluid and contribute to hydrocephalus. In most cases, affected children have no other symptoms. But a small number develop serious problems, such as breathing and swallowing difficulties and upper body weakness. In these cases, doctors may recommend surgery to relieve pressure on the brain.
    • Tethered spinal cord: Most children with myelomeningocele, and a small number with meningocele or spina bifida occulta, have a tethered spinal cord. This means that the spinal cord does not slide up and down with movement as it should, because it is held in place by surrounding tissue. Some children have no symptoms, but others develop leg weakness, worsening leg function, scoliosis (curvature of the spine), pain in the back or legs, and changes in bladder function. Doctors usually recommend surgery to release the spinal cord from surrounding tissue. After surgery, a child should return to his usual level of functioning.
    • Urinary tract disorders: Because of nerve damage, individuals with myelomeningocele often have problems emptying the bladder completely. This can lead to urinary tract infections and kidney damage. A technique called intermittent catheterization, in which the parent or child inserts a plastic tube into the bladder several times a day, is often helpful. Children with spina bifida should have regular care by a urologist (a doctor who specializes in urinary tract problems) to help prevent urinary tract problems.
    • Latex allergy: According to the Spina Bifida Association (SBA), many children with myelomeningocele are allergic to latex (natural rubber), possibly due to repeated exposures during surgeries and medical procedures (4). Symptoms include watery eyes, wheezing, hives, rash and even life-threatening breathing problems. Doctors should consider using nonlatex gloves and equipment during procedures on individuals with spina bifida. Affected individuals and their families should avoid latex items often found in the home and community, such as most baby bottle nipples, pacifiers and balloons. A list of safe and unsafe items is available from the Spina Bifida Association.
    • Learning disabilities: At least 80 percent of children with myelomeningocele have normal intelligence (4). However, some have learning problems.
  • Other conditions: Some individuals with myelomeningocele have additional physical and psychological problems, such as obesity, digestive tract disorders, depression and sexual issues.With treatment, children with spina bifida usually can become active individuals. Most live normal or near-normal life spans (6).

Can spina bifida be prevented?
A B-vitamin called folic acid can help prevent spina bifida and other NTDs. Studies show that if all women in the United States took the recommended amount of folic acid before and during early pregnancy, up to 70 percent of NTDs could be prevented(1). It is important for a woman to have enough folic acid in her system before pregnancy and during the early weeks of pregnancy, before the neural tube closes.

The March of Dimes recommends that all women of childbearing age take a multivitamin with 400 micrograms of folic acid every day before pregnancy and during early pregnancy. However, a woman should not take more than 1,000 micrograms (or 1 milligram) without her provider’s advice.

Healthy eating includes eating foods that are fortified with folic acid and foods that contain folate, the natural form of folic acid that is found in foods. Many grain products in the United States are fortified with folic acid. This means that a synthetic (manufactured) form of folic acid is added to them. Enriched flour, rice, pasta, bread and cereals are examples of fortified grain products. (A woman can check the label to see if a product is enriched.) Folate-rich foods include leafy green vegetables, beans and orange juice.

Women who already have had a baby with spina bifida or another NTD, as well as women who have spina bifida, diabetes or seizure disorders, should consult their health care provider before another pregnancy about the amount of folic acid to take. Studies have shown that taking a ten-fold larger dose of folic acid daily (4 milligrams), beginning at least 1 month before pregnancy and in the first trimester of pregnancy, reduces the risk of having another affected pregnancy by about 70 percent (2,7).

Can spina bifida be detected prenatally?
Health care providers routinely offer pregnant women screening tests to help identify fetuses at increased risk of spina bifida. These screening tests include a blood test called the quad screen and an ultrasound. The blood testmeasures the levels of four substances in the mother’s blood to identify pregnancies at higher-than-average risk of spina bifida and other NTDs, as well as Down syndrome and certain related birth defects.

If the screening test suggests an increased risk of spina bifida, the health care provider may recommend additional tests that are accurate in detecting severe spina bifida. The tests are a detailed ultrasound of the fetal spine andamniocentesis. A detailed ultrasound can help determine the seriousness of spina bifida and whether certain complications are present. In amniocentesis, the doctor inserts a needle into the woman’s uterus to take a small sample of amniotic fluid. The fluid is sent to a lab to measure levels of alpha-fetoprotein (AFP) in the fluid. An abnormal amount of the protein in the fluid is associated with spina bifida.

What are the benefits of detecting spina bifida before birth?
When spina bifida is diagnosed early in pregnancy, women can consult with their health care provider to learn more about the disorder and to consider their options. For example, they can plan for delivery in a specially equipped medical center so that the baby can have any necessary surgery or treatment soon after birth.

Parents and doctors also can discuss whether a vaginal or cesarean delivery would be best for their baby. Fetuses with myelomeningocele are more likely than other babies to be in a breech (feet-first) position. A cesarean deliveryis generally recommended for these babies (2). Some doctors may recommend a cesarean delivery for babies with myelomeningocle who are in a normal head-first position, especially if they have a large cyst (3,8). One study found that a planned cesarean delivery can reduce the severity of paralysis in babies with myelomeningocele; however, several studies found no reduction in paralysis in babies delivered by cesarean (2,8,9).

More than 400 babies have undergone experimental prenatal surgery to repair myelomeningocele before birth( 10). This approach is based on the idea that early repair (between the 19th and 25th weeks of pregnancy) may help prevent damage to exposed spinal nerve tissue in the womb and reduce paralysis and other complications. Preliminary results suggest that children who have prenatal surgery have improvements in the Chiari malformation and may need a hydrocephalus shunt less frequently, but their bladder and bowel function do not appear to be improved (2,3). One study found better-than-expected walking ability in toddlers, but other studies did not (3,11). This procedure poses surgery-related risks to mother and baby and puts the baby at high risk of premature delivery(before 37 completed weeks of pregnancy). Prematurity increases the risk of health problems during the newborn period and lasting disabilities. Doctors do not yet know whether the benefits of prenatal surgery outweigh these risks.

To find out whether prenatal or postnatal surgery is more effective, the National Institute of Child Health and Human Development (NICHD), a part of the National Institutes of Health (NIH), is conducting a study to compare the results of both types of surgery in 200 babies with myelomeningocele( 6). Half of the babies undergo surgery before birth, while the other half have surgery shortly after birth. The surgery is being carried out at three major medical centers: Children’s Hospital of Philadelphia, the University of California at San Francisco and Vanderbilt University Medical Center in Nashville. More about this research is available at the study Web site or (866)-ASK-MOMS (866-275-6667).

Where can families find additional information on spina bifida?
More information is available from:

References

  1. Centers for Disease Control and Prevention (CDC). Spina Bifida. Created 3/11/09.
  2. American College of Obstetricians and Gynecologists (ACOG). Neural Tube Defects. ACOG Practice Bulletin, number 44, July 2003 (reaffirmed 2008).
  3. Fichter, M.A., et al. Fetal Spina Bifida Repair – Current Trends and Prospects of Intrauterine Neurosurgery. Fetal Diagnosis and Therapy, 2008, volume 23, pages 271-286. \
  4. Spina Bifida Association. About Spina Bifida, accessed 6/12/09.
  5. Jallo, G.I., et al. Endoscopic Third Ventriculostomy. Neurosurg Focus, volume 19, number 6, E11, December 2005.
  6. Management of Myelomeningocele Study. About Spina Bifida, accessed 6/9/09.
  7. Centers for Disease Control and Prevention (CDC). Folic Acid. Updated 3/31/09.
  8. Hamrick, S.E.G. Cesarean Delivery and Its Impact on the Anomalous Infant. Clinics in Perinatology, volume 35, 2008, pages 395-406.
  9. Luthy, D.A., et al. Cesarean Section Before the Onset of Labor and Subsequent Motor Function in Infants with Meningomyelocele Diagnosed Antenatally. New England Journal of Medicine, volume 324, 1991, pages 662-666.
  10. Sutton, L.N. Fetal Surgery for Neural Tube Defects. Best Pract Res Clin Obstet Gynaecol, February 2008, volume 22, number 1, pages 175-188.
  11. Danzer, E., et al. Lower Extremity Neuromotor Function and Short-Term Ambulatory Potential Following In Utero Myelomeningocele Surgery. Fetal Diagnosis and Therapy, 2009, volume 25, pages 47-53.

August 2009