Open Neural Tube Defects (ONTDs)

Neural tube defects are problems with the way the brain, spinal cord, or spine forms before birth. These problems occur in about 1 in every 1,500 newborn babies each year.

What are open neural tube defects?

During pregnancy, the brain and spine begin as a flat plate of cells. This plate of cells then rolls into a tube, called the neural tube. If all or part of the neural tube fails to close, this leaves an opening. This is known as an open neural tube defect, or ONTD. This opening may be left exposed, or covered with bone or skin.

The types of neural tube defects include:

  • Spina bifida. Spina bifida is when the spine doesn’t grow normally over the spinal cord. Babies born with spina bifida may have minor or temporary problems. Or they may have permanent, often serious, physical problems. These may include paralysis, lack of bowel and bladder control, club feet, a buildup of spinal fluid in the head (hydrocephaly), and intellectual disability. In most cases, the child may need one or more surgeries after birth.

  • Anencephaly. This defect is when part of the brain and skull don’t form. It occurs when the neural tube doesn’t close at the base of the skull. Babies with anencephaly are often stillborn or only live for a very short time after birth.

  • Encephalocele. This is a very rare condition. With this defect, the brain or its coverings poke through the skull.

Anencephaly and spina bifida are the most common ONTDs.

What causes open neural tube defects?

In most cases, ONTDs occur in children without any family history of these defects. They result from a mixture of genes inherited from both parents plus environmental factors. These factors may include uncontrolled diabetes in the mother and use of some prescription medicines. ONTDs happen 5 times more often in females than males. When a child is born with an ONTD, the family has a higher chance for an ONTD in a future baby. The type of ONTD can differ in the same family. For example, one child may have anencephaly, and another may have spina bifida.

How open neural tube defects are diagnosed

ONTDs can be diagnosed before birth. The first step is to check for increased risk. Pregnant women should have a blood test around 15 to 20 weeks of pregnancy. This test is called maternal serum screening. It’s also called the double, triple, or quadruple screen. The test is used to see if the baby is at higher risk for an ONTD.

If the baby is at a higher risk, these additional tests may be done:

  • Amniocentesis. This test is done by removing a small amount of fluid from inside the amniotic sac around the baby. The amount of a protein called alpha-fetoprotein (AFP) in the fluid is measured.

  • Fetal ultrasound. This tests uses sound waves to create images of the baby in the womb on a computer screen. In some cases, ultrasound during pregnancy may be able to show an ONTD, but not always.

Can open neural tube defects be prevented?

Folic acid is a B vitamin that can reduce the chance for neural tube defects. The neural tube closes 28 to 32 days after a baby is conceived. This is before many women are aware they are pregnant. For this reason, experts advise all women of child-bearing age to take a multivitamin that has folic acid.

If a couple has had a previous child with an ONTD, a larger amount of folic acid is advised. The CDC advises that a woman take 4 mg (4,000 mcg) of folic acid one month before becoming pregnant. For this amount of folic acid, you’ll need a prescription from your healthcare provider.