Neural tube defects

Neural tube defects (NTDs) are birth defects of the brain and spinal cord. They happen in about 3,000 pregnancies each year in the United States.

A baby’s neural tube normally develops into the brain and spinal cord. It starts out as a tiny, flat ribbon that turns into a tube by the end of the first month of pregnancy. NTDs happen if the tube doesn’t close completely. NTDs can cause serious problems for babies, including death.

If women of childbearing age take 400 micrograms of folic acid every day before and during early pregnancy, it can help reduce their baby's risk for NTDS. Folic acid is a B vitamin that every cell in your body needs for normal growth and development.

What is spina bifida?

Spina bifida is the most common NTD. It affects about 1,500 babies a year in this country. In this condition, the tiny bones of the vertebrae do not close completely, and a part of the spinal cord pokes through the spine.

Spina bifida sometimes can be treated with surgery before or after birth. But children with spina bifida may have paralyzed legs and problems controlling their bladder and bowel (going to the bathroom). There also are milder forms of spina bifida that cause fewer problems for children.

What is anencephaly?

Anencephaly is one of the most severe NTDs. It affects about 1,000 babies each year in this country. Babies with this condition are missing major parts of the brain, skull and scalp. They do not survive long after birth, usually for just a few hours.

Anencephaly occurs when the upper part of the neural tube that forms the brain does not close completely. Babies with this condition often have other birth defects of the head and face, as well as defects in other parts of the body.

Girls are three times more likely than boys to have anencephaly.

What is an encephalocele?

Encephalocele is a rare NTD that affects the brain and skull. About 375 babies are born with this NTD in the United States each year.

In this condition, a sac that contains the membranes that cover the brain pokes through an opening in the skull. Often, part of the brain pokes through, too. These conditions usually happen:

  • At the base of the skull where it meets the neck (the most common site)
  • Between the forehead and nose
  • In middle of the upper part of the skull

Babies with encephalocele generally need surgery to place parts of the brain back inside the skull and close the opening.

Some babies have a build-up of fluid in the brain. This is called hydrocephalus. Babies with this condition are treated with surgery to insert a tube (called a shunt) into the brain. The shunt drains excess fluid. The shunt runs under the skin into the chest or abdomen, and the fluid passes into the child’s body. The fluid does not hurt other parts of the child’s body.

The outlook for children with encephalocele depends on the location of the opening, the parts of the brain that are affected, and whether or not they have other birth defects. At least half of all children with encephalocele have other birth defects, including defects of the head and face. About 20 percent are stillborn. Stillborn means that a baby dies in the womb after 20 weeks of pregnancy but before birth.

Lasting disabilities for children with encephalocele can include:

  • Intellectual disabilities. These happen in about 75 percent of children with encephalocele. The remaining 25 percent may have normal intelligence.
  • Movement problems or paralysis (not being able to move)
  • Vision problems
  • Seizures

What causes NTDs?

We’re not exactly sure what causes NTDs. There may be one or several causes, including:

  • Genetics. This means a baby inherits the condition from his parents. Parents pass traits like eye and hair color and sometimes birth defects to their children through genes.
  • Environment. This is things that you come in contact with in everyday life. Some can be harmful to a pregnancy, like air pollution, lead and cigarette smoke. 

Who is at risk of having a baby with an NTD?

Anyone can have a baby with an NTD. But some are more likely than others:

  • Couples with a family history of NTDs. This means you’ve already had a baby with an NTD or someone in your family has had a baby with an NTD. A couple with one child with an NTD has a 4 out of 100 chance (4 percent) of having another baby with an NTD. A couple with two affected children has a 1 in 10 chance (10 percent) chance of having another baby with an NTD. If you have a family history of NTDs, see a genetic counselor to discuss risks of NTDs to your future children.
  • Women who take certain anti-seizure medications. If you take medicine to prevent seizures, talk to your health care provider before you get pregnant about how the medicine may affect your pregnancy.
  • Women who are obese. Some studies show that being obese increases your risk for having a baby with an NTD. Talk to your provider about getting to a healthy weight before pregnancy.
  • Women who have diabetes. Diabetes is a medical condition in which your body has too much sugar (called glucose) in their blood.
  • Certain groups of people. In North America, Hispanics are at highest risk of having a baby with an NTD, followed by whites. NTDs are less common among Ashkenazi Jews, blacks and most Asians. 

How can you help prevent NTDs in your baby?

Taking the B-vitamin folic acid can help prevent NTDs. It’s important to have enough folic acid in your system before pregnancy and during early pregnancy, before the neural tube closes.

The March of Dimes recommends that all women of childbearing age take a multivitamin with at least 400 micrograms of folic acid every day before pregnancy and during early pregnancy. You can take up to 1,000 micrograms each day. But don’t take more than 1,000 micrograms unless you talk to your provider first.

You need folic acid when you’re pregnant, too. During pregnancy, take a prenatal vitamin that has at least 600 micrograms of folic acid in it every day.

If you’ve already had a pregnancy affected by an NTD, you need even more folic acid. Take at least 4,000 micrograms of folic acid each day, starting at least 1 month before pregnancy and during the first trimester of pregnancy. Studies show that taking this amount before and during early pregnancy can help reduce your risk of having another baby with an NTD by about 70 percent. Women with spina bifida, diabetes or seizure disorders also need this much folic acid every day. Talk to your provider about how to get this much folic acid.

Can you get folic acid from food?

Yes. Some foods have folic acid added to them. Look for the word “fortified” or “enriched” on the package label. Foods with added folic acid include:

  • Bread
  • Breakfast cereal
  • Cornmeal
  • Flour
  • Pasta
  • Products made from a kind of flour called corn masa, like tortillas, tortilla chips, taco shells, tamales and pupusas
  • White rice

You also can get folic acid from some fruits and vegetables. When folic acid is naturally in a food, it’s called folate. Good sources of folate are:

  • Beans
  • Leafy green vegetables
  • Orange juice

You have to eat a lot of these foods to get the right amount of folic acid every day. So even if you eat them, remember to take your vitamin, too.

Can NTDs be detected before birth?

Yes. Health care providers routinely offer pregnant women screening tests to help identify babies that are at increased risk of having an NTD. These screening tests include:

  • Quad screen. This blood test measures four substances in a mother’s blood to tell if her pregnancy is at an increased risk of having an NTD, other than encephalocele.
  • Ultrasound. This test can help detect pregnancies at increased risk of encephalocele and other NTDs.

If a screening test shows an increased risk of NTDs, your provider may recommend additional tests, such as amniocentesis and a detailed ultrasound of the baby’s skull and spine.

What are the benefits of detecting an NTD before birth?

If an NTD is diagnosed early in pregnancy, you can talk to your health care provider to learn more about your baby’s condition and birth and treatment options. For example:

  • You can plan to have your baby in a medical center that specializes in caring for babies with NTDs. This way your baby can have any necessary surgery or treatment soon after birth.
  • You can talk to your provider about whether a vaginal or cesarean birth is better for your baby.
  • Your baby may be able to have surgery to repair spina bifida before birth, while still in the womb. More than 400 babies have had this kind of surgery. Research shows that surgery on a baby to repair spina bifida while still in the womb is more effective than surgery after birth. 

Does the March of Dimes support research on NTDs?

Yes. A number of researchers supported by the March of Dimes are looking for genes that may contribute to NTDs. Others are working to better understand how folic acid prevents NTDs.

More information

See also: Your first prenatal checkupLater prenatal checkups

Last reviewed: April, 2016