Neural Tube Defects

Overview

Neural tube defects (NTDs) are a group of birth defects affecting the brain, spine, or spinal cord. They happen very early in pregnancy, usually within the first month, when the neural tube, the structure that becomes the brain and spinal cord, does not close completely. Because this occurs so early, often before a woman knows she is pregnant, prevention focuses on the time before and around conception.

The two most common neural tube defects are spina bifida, where the spine and spinal cord do not form properly, and anencephaly, a serious defect in which major parts of the brain and skull do not develop. The severity ranges widely. Crucially, getting enough folic acid before and during early pregnancy substantially reduces the risk of these defects.

The neural tube is the early structure from which the brain and spinal cord develop, and it normally seals closed within the first few weeks after conception. If part of it fails to close, the brain, spinal cord, or the bones and skin that cover them do not form completely, producing the different types of neural tube defect depending on where along the tube the problem occurs. Because this all happens so early, often before a woman realizes she is pregnant, prevention efforts focus on ensuring adequate folate is already on board at the time of conception. Public health measures such as adding folic acid to flour and grains in many countries have reduced the number of affected pregnancies.

Types and Symptoms

Neural tube defects vary in type and severity:

• Spina bifida: Ranges from a mild, hidden form with no symptoms to more severe forms with an exposed sac on the back. Severe forms can cause leg weakness or paralysis, bladder and bowel problems, and fluid on the brain.
• Anencephaly: A severe defect in which much of the brain and skull are missing; it is not compatible with long-term survival.
• Encephalocele: A sac-like protrusion of brain tissue through an opening in the skull.

Many defects are detected before birth on ultrasound. The symptoms a child has depend on the type and location of the defect.

Causes

Neural tube defects result from incomplete closure of the neural tube early in development. The exact cause in any individual is often a combination of genetic and environmental factors. Contributing factors include:

• Folate (folic acid) deficiency: Insufficient folate around conception is a major modifiable factor.
• Genetic factors: Including a family history of NTDs.
• Certain medications: Some anti-seizure drugs raise the risk.
• Maternal health conditions: Such as poorly controlled diabetes and obesity.

Risk Factors

• Low folate intake before and during early pregnancy
• A previous pregnancy affected by a neural tube defect
• A family history of NTDs
• Poorly controlled diabetes before pregnancy
• Taking certain anti-seizure medications
• Significant obesity
• High fever or certain illnesses in early pregnancy

Diagnosis

Neural tube defects are often found during routine pregnancy care:

• Prenatal ultrasound: Can show spina bifida, anencephaly, and other defects.
• Maternal blood screening: A blood test measuring a marker (alpha-fetoprotein) may be raised with open neural tube defects.
• Detailed (fetal) ultrasound and sometimes MRI: To assess the type and severity.
• Amniocentesis: Occasionally used for further information.

After birth, examination and imaging confirm the type and guide care.

Treatment

Treatment depends on the type and severity of the defect and is led by a specialist team.

• Surgery for spina bifida: Closure of the spinal opening shortly after birth, or in some cases surgery before birth, to protect the spinal cord.
• Managing complications: Treatment for fluid on the brain (hydrocephalus), and support for bladder, bowel, and mobility problems.
• Ongoing care: Physical therapy, orthopedic care, bladder and bowel management, and support for development and education.

Children with spina bifida are usually cared for by a team that may include neurosurgeons, urologists, orthopedic specialists, physical and occupational therapists, and others, working together over many years. The needs depend on the level and severity of the defect: some children have minimal effects, while others need help with mobility, continence, and learning. Anencephaly, by contrast, cannot be corrected, and care focuses on comfort and support for the family. With modern, coordinated care, the outlook for spina bifida has improved greatly, and many people live full and independent lives.

Prevention

• Take folic acid daily before conception and through early pregnancy, as advised by a health professional
• People who could become pregnant are often advised to take folic acid even when not planning pregnancy
• A higher dose may be recommended for those at higher risk, such as a previous affected pregnancy, on a doctor's advice
• Manage diabetes well before pregnancy
• Review any anti-seizure or other medications with a doctor when planning pregnancy
• Eat folate-rich foods such as leafy greens, legumes, and fortified grains

When to See a Doctor

If you are planning a pregnancy or could become pregnant, speak with a health professional about taking folic acid, ideally before conception. Seek advice promptly if you:

• Have had a previous pregnancy affected by a neural tube defect
• Take anti-seizure medication or have diabetes
• Have a family history of NTDs

During pregnancy, attend recommended screening appointments, and discuss any abnormal screening results with your care team so that further testing and planning can be arranged.

Related Topics

Frequently Asked Questions

References

1. Centers for Disease Control and Prevention (CDC). Neural Tube Defects.
2. National Institute of Child Health and Human Development (NICHD).
3. Mayo Clinic. Spina bifida.
4. MedlinePlus, U.S. National Library of Medicine. Neural tube defects.