What Is a Neural Tube Defect?

Medically Reviewed by Poonam Sachdev on October 07, 2022
5 min read

What is a neural tube defect?

A neural tube defect is a severe birth defect of the brain or spine. These occur when the neural tube, which forms the early brain or spine in a developing baby, doesn't close properly. 

There are several types of neural tube defects. Spina bifida and anencephaly are the two most common conditions caused by these defects.

Sometimes, neural tube defects occur during pregnancy with no known cause. However, there are also factors that can contribute to their likelihood, including genetics, nutrition, and exposure to environmental toxins. 

The following factors may make your baby more likely to develop a neural tube defect in utero:

  • Using a hot tub or sauna while pregnant
  • Having a high fever during pregnancy
  • Lacking appropriate amounts of folic acid in your diet before and during pregnancy
  • Being obese
  • Taking certain medications for seizures during pregnancy, including Dilantin, Tegretol, Depakote, or antifolate
  • Taking non-steroidal anti-inflammatory drugs (NSAIDS) early on in the pregnancy
  • Using opioids during pregnancy
  • Taking sulfonamides, a type of antibiotic, during pregnancy
  • Having high blood sugar close to the time of conception if you have diabetes
  • Having a family history of neural tube defects

Experts also believe that exposure to chemicals and pollutants in the environment such as lead and cigarette smoke may also increase the risk of neural tube defects.

Neural tube defects develop while your baby is still in your uterus. There aren't any obvious external symptoms of a neural tube defect, so doctors will perform tests at key points during pregnancy to make sure your baby is developing properly.

Once born, your baby may have the following symptoms as a result of a neural tube defect, depending on what type of defect they have:

  • Paralysis
  • Lack of control over bowels and urination
  • Blindness
  • Deafness
  • Intellectual disability
  • Stillbirth (death)

Neural tube defects affect each person differently. Some are only affected in minor ways by a neural tube defect, while others are profoundly affected.

Your doctor will order specific tests at important milestones during your pregnancy to check (in part) for neural tube defects:

  • First-trimester ultrasound. You should get an ultrasound between 11 and 14 weeks of pregnancy to check on the development of your baby.
  • Amniocentesis. This test is not performed during every pregnancy, but it can help diagnose neural tube defects. During this test, your doctor will take a sample of your amniotic fluid to test for signs of neural tube defects or other pregnancy complications. Performing an amniocentesis does have risks, but if your doctor recommends it, they likely believe the risks outweigh the benefits.
  • Alpha-fetoprotein blood test. Your doctor will test for elevated levels of this protein using a blood test when you are between 16 and 18 weeks pregnant. Up to 80% of people carrying a baby with a neural tube defect have higher levels of alpha-fetoprotein than normal.
  • Second-trimester ultrasound. Your second ultrasound should take place between 18 and 22 weeks of your pregnancy to check your baby's development.

There are several types of neural tube defects.

Spina bifida. This condition occurs when your baby's spinal cord doesn't fully close during the third and fourth weeks of pregnancy. When your child is born with this condition, part of their spine is exposed. There are three subtypes of spina bifida:

  • Occulta. In this minor form of spina bifida, there are usually no symptoms. There is only a small gap in the vertebrae. Only 1 in 1,000 people with this condition experience resulting neurological symptoms like lack of bowel or bladder control, back pain, or scoliosis.
  • Meningocele. In this rare form of spina bifida, the spinal cord and nerves are fully intact but the bones have not fully closed around the spinal cord. The spinal cord consequently bulges out of the spinal column, protected by the meninges, a triple protective layer that surrounds the spine with a fluid-filled sac. This type of spina bifida can often be corrected with surgery and may cause only minor symptoms.
  • Myelomeningocele. This form of spina bifida accounts for 3/4 of all spina bifida cases and is the most severe. In cases with this condition, the spinal cord bulges out of the back, not protected by anything, leaving the nerves exposed. This condition can result in paralysis of the legs and loss of bladder and bowel control, depending on where the spine is affected. Surgery before or after birth may help treat this condition, though.

Anencephaly. If the neural tube does not close properly at the top, anencephaly may develop. Babies born with anencephaly are missing their cerebrum and the forebrain, two essential parts of the brain. The rest of their brain is often exposed, with no skin or skull covering it. 

Encephalocele. Encephalocele is another defect that occurs toward the top of the neural tube. In the case of this condition, part of your baby's brain is held in a sac outside of the skull. It protrudes most often at the back of the skull but may protrude anywhere from the nose to the base of the skull. This condition is usually corrected with surgery, but even after surgery, some neurological symptoms may remain.

Tethered spinal cord syndrome. Your child's spinal cord is connected abnormally to the surrounding tissue. If it is not detected, a sudden spinal injury can occur.

Maintaining generally good health and monitoring any existing conditions before and during pregnancy can help to lower the risk of neural tube defects. Also consider the following tips:

  • Take 400mcg of folate daily, typically in the form of folic acid. Since the discovery that supplementing with folic acid can reduce the risk of neural tube defects, rates of these birth defects have gone down significantly.
  • Avoid hot tubs and saunas during pregnancy.
  • Take acetaminophen instead of ibuprofen or other NSAIDs.
  • Use medications to reduce a fever promptly during pregnancy.
  • Talk to your doctor about changing medications that may cause neural tube defects during pregnancy. Never stop taking a medication suddenly without your doctor's approval, though.

Show Sources

American Association of Neurological Surgeons: "Spina Bifida."
Centers for Disease Control and Prevention: "Facts about Anencephaly," "Facts about Encephalocele," "5 Ways to Lower the Risk of Having a Pregnancy Affected by a Neural Tube Defect."
Cleveland Clinic: "Neural Tube Defects (NTD)."
Eunice Kennedy Shriver National Institute of Child Health and Human Development: "What causes neural tube defects (NTDs)?"
Johns Hopkins Medicine: "Neural Tube Defects."
March of Dimes: "NEURAL TUBE DEFECTS."
Mayo Clinic: "Amniocentesis."

View privacy policy, copyright and trust info