Neural Tube Defects (NTD)

Neural tube defects (NTDs) are birth defects (congenital conditions) of the brain, spine or spinal cord. They happen to developing fetuses within the first month of pregnancy — often before you even know you’re pregnant. The two most common neural tube defects are spina bifida and anencephaly.

Normally, during your first month of pregnancy, the two sides of the fetus’s spine join together to cover and protect the spinal cord, spinal nerves and meninges. At this point, the developing brain and spine are called the neural tube.

As growth continues, the top of the neural tube becomes the brain. The rest of the tube becomes the spinal cord. An NTD happens when this tube doesn’t close completely somewhere along its length.

Neural tube defects affect about 3,000 pregnancies each year in the United States.

Types of this condition

Types of neural tube defects include:

• Spina bifida
• Anencephaly
• Encephalocele
• Iniencephaly

Spina bifida

Spina bifida is the most common type of neural tube defect (NTD). It happens when the neural tube doesn’t close completely somewhere along the spine during fetal development.

Types of spina bifida include:

• Myelomeningocele (open spina bifida): This leads to a fluid-filled sac that sticks out from your baby’s back. It contains part of their spinal cord, meninges, nerves and cerebrospinal fluid (CSF).
• Meningocele: This leads to a sac of fluid that sticks out through an opening in your baby’s back. But their spinal cord isn’t involved or damaged.
• Spina bifida occulta: This creates a small gap in your baby’s spine. But there isn’t an opening or sac on their back. It’s the mildest form of spina bifida.

Anencephaly

Anencephaly happens when the fetus’s neural tube doesn’t close at the top. This causes the skull, scalp and brain not to develop properly. Portions of the brain and skull are missing. The brain tissue that does form is usually exposed because there isn’t enough skin and bone to cover it.

Infants with anencephaly are either stillborn or die soon after birth.

Encephalocele

Encephalocele happens when the neural tube doesn’t close near the brain. There’s also an opening in the skull. The fetus’s brain and the membranes that cover it can protrude through the skull, forming a sac-like bulge.

In some cases, there’s only a small opening in the nasal cavity or forehead area that’s not noticeable.

Iniencephaly

Iniencephaly happens when the spine is severely misshapen. It often causes a lack of a neck. The fetus’s head may be bent severely backward. The facial skin is connected to the chest. And the scalp is connected to the back.

Babies with iniencephaly are usually stillborn.

Symptoms of neural tube defects

Each type of neural tube defect has different symptoms or features. But there’s no way to know you’re carrying a fetus with an NTD without medical tests, like an ultrasound.

If your healthcare provider suspects a neural tube defect, they’ll provide more information about what to expect. NTDs affect each baby differently.

Neural tube defect causes

Healthcare providers and scientists don’t know the exact cause of neural tube defects. But they believe it’s a complex combination of genetic, nutritional and environmental factors.

In particular, low levels of folate before and during early pregnancy appear to play a role.

Risk factors

Any woman can have a baby with an NTD. But certain factors increase the risk, including:

• Folate deficiency: Folate is important for healthy fetal development.
• History of neural tube defects: If you’ve had one baby with an NTD, you have a 2% to 3% increased risk of having another baby with an NTD.
• Certain antiseizure medications: These medications, especially valproic acid (valproate), are linked to neural tube defects when taken during pregnancy.
• Preexisting diabetes: Having poorly managed diabetes during pregnancy puts you at a higher risk of having a baby with an NTD.
• Obesity: If you have obesity before pregnancy, you have an increased risk of having a baby with an NTD.
• Increased body temperature in early pregnancy: Increases in core body temperature (hyperthermia) in the early weeks of pregnancy have been associated with a slightly increased risk of NTDs. This may be due to a prolonged fever or use of a sauna or hot tub.

Complications of this condition

Some babies born with NTDs have no complications, while others have serious disabilities. Babies with iniencephaly and anencephaly are typically stillborn or die shortly after birth due to complications.

General complications of NTDs can include:

• Bladder and bowel control issues
• Blindness
• Deafness
• Excess fluid around their brain (hydrocephalus)
• Intellectual disability
• Paralysis

How doctors diagnose this condition

Healthcare providers typically diagnose NTDs during pregnancy through prenatal tests, like:

• Alpha-fetoprotein (AFP) blood test: This screening blood test measures your AFP level during the 16th to 18th week of pregnancy. The amount is higher than normal in about 75% to 80% of pregnant women who are carrying a fetus with an NTD. If your level is elevated, your healthcare provider will order other tests to better evaluate the growing fetus.
• Prenatal ultrasound: An ultrasound during pregnancy is the most accurate method to diagnose several NTDs. Providers typically recommend ultrasounds during the first trimester (11 to 14 weeks of pregnancy) and second trimester (18 to 22 weeks of pregnancy).
• Amniocentesis: Providers use this test to check for NTDs and other birth defects. During amniocentesis, they use a needle to remove a sample of fluid from the amniotic sac that surrounds the fetus. You can get this test at 15 to 20 weeks of pregnancy. It carries certain risks.

Healthcare providers also use imaging tests, like MRI or CT scans, to diagnose some NTDs after birth.

How is it treated?

There are several treatment options for spina bifida and encephalocele, depending on the severity of the condition. Surgery is a common option for both.

Anencephaly and iniencephaly aren’t treatable. Infants with these conditions are typically stillborn or die shortly after birth.

Treatment for spina bifida and encephalocele

Healthcare providers typically treat encephalocele with surgery to place the protruding part of your baby’s brain and the membranes covering it back into their skull. They then close the opening in your baby’s skull.

Treatment for myelomeningocele usually involves surgery to repair the opening in your baby’s spine. Surgeons can do this before birth (fetal surgery) or shortly after birth.

Long-term treatment for both conditions depends on your child’s case. They may need multiple surgeries over time. Or they may need other treatments related to complications, like a shunt to drain excess fluid surrounding their brain.

What can I expect?

No two people with a neural tube defect, especially spina bifida and encephalocele, are affected in the same way. The best way you can prepare is to talk to healthcare providers who specialize in researching and treating these conditions.

If your child was born with an NTD, they’ll likely need to see their healthcare team regularly as they grow.

Can this be prevented?

It’s not always possible to prevent NTDs. But there are several steps you can take to try to lower the risk.

One key way is to make sure you’re getting enough folate and folic acid. A folate deficiency before and during pregnancy increases the risk of having a baby with spina bifida and other NTDs.

Folate and folic acid are forms of vitamin B9. They support healthy cell growth and development, especially in early pregnancy. Folate occurs naturally in foods. It refers to all types of vitamin B9, including folic acid. Folic acid is a manufactured form of B9 found in supplements. It’s also added to certain foods.

The general recommendation is to take 400 micrograms (mcg) of folic acid per day if you’re at average risk of carrying a fetus with an NTD. If you’re at high risk, your healthcare provider may have you take more. Eating foods with folate is also important. These include dark leafy greens, legumes, citrus fruits, and nuts and seeds.

Other preventive steps include:

• Managing diabetes and/or obesity before getting pregnant
• Talking to your provider before getting pregnant if you take antiseizure medications
• Avoiding hot tubs and saunas during pregnancy
• Contacting your healthcare provider if you have a fever (100.4 degrees Fahrenheit, or 38 degrees Celsius, and above) during pregnancy