NTDs (neural tube defects) are birth defects that occur very early in pregnancy. The defects develop between the 17th and 30th day after conception (four to six weeks after the first day of a woman's last menstrual period), usually before a woman knows she is pregnant. During this critical time of pregnancy, the proper formation and closure of the neural tube, which later becomes the spinal cord, brain and bone surrounding the spinal cord and brain, normally takes place. An NTD occurs when the neural tube fails to close properly.
Anencephaly and spina bifida are the two most common NTDs. Anencephaly is a fatal condition in which the upper end of the neural tube fails to close. In these cases, the brain fails to develop completely or is entirely absent. Pregnancies affected by anencephaly often result in miscarriages, and the infants who are born alive die very soon after birth.
Spina bifida occurs when the lower end of the neural tube fails to close. As a result, the spinal cord and backbones do not develop properly. Sometimes a sac of fluid protrudes through an opening in the back, and often a portion of the spinal cord is contained in this sac. Paralysis of the infant's legs, loss of bowel and bladder control, hydrocephalus ("water on the brain") and learning disabilities are often associated with spina bifida. Eighty to 90 percent of infants born with spina bifida survive. Despite varying degrees of disability, many lead long, successful and productive lives.
What is it Like to Live With an NTD?
Both prevention and treatment of NTDs - spina bifida and anencephaly - are important. NTDs impact not only the life of a child and those of his or her family, but the community as well. As a child with spina bifida grows older, he or she faces unique economic, educational, medical, health and emotional issues. Paralysis of the legs and bowel and bladder management problems are common for those with spina bifida. These problems may affect a person's health, self-esteem, personal interactions and work and recreational opportunities.
Despite physical and mental challenges, many people with spina bifida live independently. Today, mental retardation caused by hydrocephalus, a complication of spina bifida, is uncommon because of early medical and surgical treatment. However, learning disabilities are common. Although medical care has greatly improved the survival rates and quality of life of children with spina bifida, the children and families affected live with varying degrees of physical and social challenges for life.
Who Is at Risk for Having a Baby With an NTD?
There are approximately 60 million women of childbearing age in the United States. Any woman who is capable of becoming pregnant could have an NTD-affected pregnancy. It is not possible to predict which women will have a pregnancy affected by an NTD. Ninety-five percent of women with NTD-affected pregnancies have no personal or family history of NTDs.
However, some risk factors are known. These include:
About Folic Acid
- A previous NTD-affected pregnancy. (This increases a woman's chance of having another NTD-affected pregnancy by approximately 20 times.)
- Maternal insulin-dependent diabetes.
- Use of anti-seizure medication. (Valproic Acid/Depakene and Carbamazapine.)
- Medically diagnosed obesity. The body-mass index is used to determine obesity.
- Exposure to high temperatures in early pregnancy. (For example, prolonged high fevers and hot-tub use.)
- Race/ethnicity. (NTDs are more common among white women than black women and more common among Hispanic women than non-Hispanic women.)
- Lower socio-economic status.
Folic acid in a vitamin supplement, when taken one month before conception and throughout the first trimester, has been proven to reduce the risk for an NTD-affected pregnancy by 50 percent to 70 percent. Folic acid, a B-vitamin, is necessary for proper cell growth and development of the embryo. Although it is not known exactly how folic acid works to prevent NTDs, its role in tissue formation is essential. Folic acid is required for the production of DNA, which is necessary for the rapid cell growth needed to make fetal tissues and organs early in pregnancy. That is why it is important for a woman to have enough folic acid in her body both before and during pregnancy.
Folate and folic acid are different terms for the same B-vitamin. While these two terms are often used interchangeably, we make some distinctions between them. Folate is the B-vitamin form found naturally in foods. Folic acid is not found in natural food sources. Folic acid is the synthetic B-vitamin form that is used in vitamin supplements and added to fortified foods. Synthetic folic acid is absorbed better than natural food folate.
Most of the folate found naturally in foods has a more complex structure than the synthetic folic acid that is found in fortified foods and vitamin supplements. The more complex structure affects the intestine's ability to process and absorb food folate. The body can absorb and use the folic acid found in vitamin supplements and fortified foods more efficiently than it can convert the food folate into a usable form. Synthetic folic acid is about twice as absorbable as naturally occurring food folate.
Can Women Get Too Much Folic Acid?
If a woman of reproductive age were to eat a bowl of fortified cereal (100 to 400 micrograms), take a vitamin containing 400 micrograms (0.4 milligram) of folic acid and eat foods rich in folate in one day, she would not have a problem with too much folic acid. Even in very high amounts, folic acid is nontoxic. Nevertheless, with the exception of women who have had a prior NTD-affected pregnancy, it is recommended that women consume no more than 1,000 micrograms of synthetic folic acid a day.
What Do These Options Mean for Women?
A diet rich in food folate is healthy and highly recommended. There are a few studies that suggest food folate may reduce the risk for NTDs. However, this is still in question. The Public Health Service's recommendation for NTD prevention is based on studies of synthetic folic acid from supplements that women took in addition to their regular diets. Fortifying the food supply is an excellent way to increase consumption of folic acid without requiring women to change their behaviors. However, fortification at the 1998 level will not prevent all folic acid-preventable NTD-affected pregnancies unless women are educated to change the way they eat.
To prevent NTDs, women will need to take a folic acid-containing vitamin daily, eat a fortified breakfast cereal containing 100 percent of the daily value of folic acid or increase their consumption of foods fortified with folic acid in addition to consuming food folate from a balanced diet.
Incorporating these behavior changes into women's lives will prevent a significant proportion of NTDs and also contribute to women's good health.