What is it?
Spina bifida is part of a group of birth defects called neural tube defects. The neural tube is the embryonic structure that eventually develops into the baby's brain and spinal cord and the tissues that enclose them.
Normally, the neural tube forms early in the pregnancy and closes by the 28th day after conception. In babies with spina bifida, a portion of the neural tube fails to develop or close properly, causing defects in the spinal cord and in the bones of the backbone.
Spina bifida occurs in various forms of severity. When treatment for spina bifida is necessary, it's done through surgery, although such treatment doesn't always completely resolve the problem.
Spina bifida occurs in three forms, each varying in severity:
- Spina bifida occulta. This mildest form results in a small separation or gap in one or more of the bones (vertebrae) of the spine. Because the spinal nerves usually aren't involved, most children with this form of spina bifida have no signs or symptoms and experience no neurological problems. An abnormal tuft of hair, a collection of fat, a small dimple or a birthmark on the newborn's skin above the spinal defect may be the only visible indication of the condition. Many people who have spina bifida occulta don't even know it, unless the condition is discovered during an X-ray or other imaging test done for unrelated reasons.
- Meningocele. In this rare form, the protective membranes around the spinal cord (meninges) push out through the opening in the vertebrae. Because the spinal cord develops normally, these membranes can be removed by surgery with little or no damage to nerve pathways.
- Myelomeningocele. Also known as open spina bifida, myelomeningocele is the most severe form — and the form people usually mean when they use the term "spina bifida." In myelomeningocele, the baby's spinal canal remains open along several vertebrae in the lower or middle back. Because of this opening, both the membranes and the spinal cord protrude at birth, forming a sac on the baby's back. In some cases, skin covers the sac. Usually, however, tissues and nerves are exposed, making the baby prone to life-threatening infections. Neurological impairment — often including loss of movement (paralysis) — is common. So are bowel and bladder problems, seizures and other medical complications.
Doctors aren't certain what causes spina bifida. As with many other problems, it appears to result from a combination of genetic and environmental risk factors, such as a family history of neural tube defects and folic acid deficiency.
Although doctors and researchers don't know for sure why spina bifida occurs, they have identified a few risk factors:
- Race. Spina bifida is more common among whites and Hispanics.
- Family history of neural tube defects. Couples who've had one child with a neural tube defect have a slightly higher chance of having another baby with the same defect. That risk increases if two previous children have been affected by the condition. In addition, a woman who was born with a neural tube defect, or who has a close relative with one, has a greater chance of giving birth to a child with spina bifida. However, most babies with spina bifida are born to parents with no known family history of the condition.
- Folate deficiency. Folate (vitamin B-9) is important to the healthy development of a fetus. Folate is the natural form of vitamin B-9. The synthetic form, found in supplements and fortified foods, is called folic acid. A folate deficiency increases the risk of spina bifida and other neural tube defects.
- Some medications. Anti-seizure medications, such as valproic acid (Depakene), seem to cause neural tube defects when taken during pregnancy, perhaps because they interfere with the body's ability to use folate and folic acid.
- Diabetes. Women with diabetes who don't control their blood sugar well have a higher risk of having a baby with spina bifida.
- Obesity. Pre-pregnancy obesity is associated with an increased risk of neural tube birth defects, including spina bifida.
- Increased body temperature. Some evidence suggests that increased body temperature (hyperthermia) in the early months of pregnancy may increase the risk of spina bifida. Elevating your core body temperature by about 3 to 4 degrees Fahrenheit above normal — about 2 degrees Celsius — due to fever or the use of saunas, hot tubs or tanning beds, has been associated with increased risk of spina bifida.
If you have known risk factors for spina bifida, talk with your doctor to determine if you need a larger dose or prescription dose of folic acid, even before a pregnancy begins. If you take medications, tell your doctor. Some medications can be adjusted to diminish the potential risk of spina bifida, if plans are made ahead of time.
Spina bifida may occasionally cause no symptoms or only minor physical disabilities. More frequently, it leads to severe physical and mental disabilities. Factors that affect the severity of complications include:
- The size and location of the neural tube defect
- Whether skin covers the affected area
- Which spinal nerves come out of the affected area of the spinal cord
Complications may include:
- Physical and neurological problems. This may include lack of normal bowel and bladder control and partial or complete paralysis of the legs. Children and adults with this form of spina bifida might need crutches, braces or wheelchairs to help them get around, depending on the size of the opening in the spine and the care received after birth.
- Hydrocephalus. Babies born with myelomeningocele also commonly experience accumulation of fluid in the brain, a condition known as hydrocephalus. Most babies with myelomeningocele will need a shunt — a surgically placed tube that allows fluid in the brain to drain as needed into the abdomen. This tube might be placed just after birth, during the surgery to close the sac on the lower back, or later as fluid accumulates.
- Meningitis. Some babies with myelomeningocele may develop meningitis, an infection in the tissues surrounding the brain. Meningitis may cause brain injury and can be life-threatening.
Additional problems may arise as children with spina bifida get older. Children with myelomeningocele may develop learning disabilities, including difficulty paying attention, problems with language and reading comprehension, and trouble learning math. Children with spina bifida may also experience latex allergies, skin problems, urinary tract infections, gastrointestinal disorders and depression.
If you're pregnant, you'll be offered prenatal screening tests to check for spina bifida and other birth defects. The tests aren't perfect. Even if the results are negative, there's still a small chance that spina bifida is present, and most mothers who have positive blood tests have normal babies. Talk to your doctor about prenatal testing, its risks and how you might handle the results. Prenatal testing is a personal choice.
The primary test used to check for myelomeningocele is the maternal serum alpha-fetoprotein (MSAFP) test. To perform this test, your doctor draws a blood sample and sends it to a laboratory, where it's tested for alpha-fetoprotein (AFP) — a protein that's produced by the fetus. It's normal for a small amount of AFP to cross the placenta and enter the mother's bloodstream, but abnormally high levels of AFP suggest that the fetus has a neural tube defect, most commonly spina bifida or anencephaly, a condition characterized by an underdeveloped brain and an incomplete skull.
Some spina bifida cases don't produce a high level of AFP. On the other hand, when a high level of AFP is found, a neural tube defect is present only a small percentage of the time. Varying levels of AFP can be caused by other factors — including a miscalculation in fetal age or multiple fetuses — so your doctor may order a follow-up blood test for confirmation. If the results are still high, you'll need further evaluation, including an ultrasound examination.
Your doctor may perform the MSAFP test with two or three other blood tests, which look for:
- Human chorionic gonadotropin (HCG), a hormone produced in the placenta
- Inhibin A, another hormone produced in the placenta
- Estriol, an estrogen produced by both the fetus and the placenta
Depending on the number of tests, the combination is called a triple screen or quadruple screen (quad screen). These tests are commonly done with the MSAFP test, but their objective is to screen for trisomy 21 (Down syndrome), not neural tube defects.
Many obstetricians rely on ultrasonography to screen for spina bifida. If blood tests indicate high AFP levels, your doctor will suggest an ultrasound exam to help determine why. The most common ultrasound exams bounce high-frequency sound waves off tissues in your body to form black-and-white images on a video monitor.
The information these images provide can help establish whether there's more than one fetus and can help confirm gestational age — two factors that can affect AFP levels. An advanced ultrasound can also detect signs of spina bifida, such as an open spine or particular features in your baby's brain that indicate spina bifida.
In expert hands, ultrasound today is quite effective in detecting spina bifida and assessing its severity. Ultrasound is safe for both mother and baby.
If a blood test shows high levels of AFP in your blood but the ultrasound is normal, your doctor may offer amniocentesis. During amniocentesis, your doctor uses a needle to remove a sample of fluid from the amniotic sac that surrounds the fetus. An analysis indicates the level of AFP present in the amniotic fluid.
A small amount of AFP is normally found in amniotic fluid. However, when an open neural tube defect is present, the amniotic fluid contains an elevated amount of AFP because the skin surrounding the baby's spine is gone and AFP leaks into the amniotic sac. A second test can be done on the same sample to reliably confirm that a neural tube defect is present.
Discuss the risks of this test, including a slight risk of loss of the pregnancy, with your doctor.