Neural Tube Defects: Spinal Bifida & Anencephaly

Neural tube defects (NTD) are congenital abnormalities which most commonly occur between the 20^th and 28^th day after an embryo is conceived. The neural plate cells make up the nervous system of a fetus. In normal fetal development, the plate folds back onto itself and creates a “neural tube.” A fully and normally formed neural tube becomes a fetal backbone and spinal cord. The superior pole will become the fetal brain, after is undergoes a series of transformations.

Anencephaly: What Is It?

Anencephaly is a neural tube defect that results when the head of a neural tube fails to properly close. Babies with anencephaly are often born without a cerebellum or scalp. Also missing in an infant born with anencephaly is the menix, which consists of both hemispheres of the brain and the vault of the skull. However, most babies with anencephaly do have a brain stem. Anencephaly can cause infant blindness, and no or few reflexes. Approximately 25% of infants with anencephaly will live to the end of pregnancy and die during delivery, 50% have a life expectancy of a few minutes to 24-hours, while the other 25% may live up to ten days.

Spina Bifida: What Is It?

With the neural tube defect Spina Bifida, a neural tube remains open at the caudal extremity. An infant with spina bifida will have a backbone and spinal cord that do not completely develop. Spina bifida causes an opening on the back, with a sac that contains liquid and possibly parts of the spinal cord. Whether or not spina bifida causes permanent disability will depend on the location of the defect on the backbone.

The higher a spina bifida lesion is on the back, the greater the chance is for lower limb paralysis. The lower the lesion is, the lower the risk of paralysis, the most frequent consequences of a lower lesion include lack of bowel and bladder control. Spina bifida can be complicated by hydrocephalus. Most babies with spina bifida will go through surgery before or right at birth, in order to prevent any further damage to the nervous system.

Neural Tube Defects: Causes

The precise causes of neural tube defects are currently unknown. Some medical researchers feel neural tube defects are the result of a combination of environmental and genetic factors.

It is never possible to predict when or if a woman will have an infant with a neural tube defect and the condition can happen in families that have no prior history of birth defects.

See Also: The Importance Of Folic Acid In Our Diet

Neural Tube Defects And Folic Acid

Folic acid and vitamin B12 are very important in reducing the number of neural tube defects. Folic acid is needed for the manufacturing and maintenance of new cells, as well as for RNA and DNA synthesis. It has been pondered that an early developing embryo might be particularly vulnerable to neural tube defects, if there is a deficiency of folic acid.

Neural Tube Defects And Vitamin B12

Vitamin B12 is an important receptor for folic acid absorption. Studies have proven a deficiency in vitamin B12 will directly contribute to the increased risk of neural tube defects. More importantly, it has not been proven that a deficiency in folic acid alone is responsible for causing neural tube defects. 

Neural Tube Defects: Other Possible Causes

Not only has folate deficiency been linked to neural tube defects, but there are also many other potential causes. The following things could lead to an increased risk of the development of neural tube defects:

• Mycotoxins
• Maternal obesity
• Maternal diabetes
• Arsenic
• Hyperthermia early in fetal development
• Radiation
• Maternal smoking
• Maternal exposure to secondhand smoke

Neural Tube Defects: Diagnosis

Testing for neural tube defects can include ultrasound examination and an amniocentesis to check maternal serum alpha-fetoprotein levels. Amniotic fluid and amniotic fluid acetylcholinesterase testing is used to confirm neural tube defects, in the event other testing indicates a positive finding. Often, neural tube defects appear at birth, but sometimes occult defects might not show up until later in life. An elevated level of maternal serum alpha-fetoprotein between the 16^th and 18^th week of pregnancy is a very good indicator of neural tube defects in a fetus.

Neural Tube Defects: Prevention Methods

Beginning in 1996, United States Food and Drug Administration published a set of regulations that required additional folic acid enrichment in breads, flour, cereals and other grains. The link between neural tube defects and folic acid deficiency is well-established. Because most women do not know they are pregnant in the first few weeks after conception, it is very important for those trying to conceive to consume a diet rich in folic acid and to possibly take a supplement containing folic acid, if the diet is not providing enough.

Prognosis

According to the Centers for Disease Control, approximately 3% of all infants born in the United States will have a neural tube defect.

Anencephaly is observed about 1 in 4,859 births, with an annual 859 cases being diagnosed. Spina bifida without anencephaly accounts for 1 in every 2,858 births and there are 1,460 new cases each year.

Folic acid helps to prevent neural tube defects. If you are a woman trying to conceive or are of child-bearing age, it is important for you to receive 400 mcg of folic acid each day, in order to protect any potential fetus from developing a neural tube defect.

See Also: Spina Bifida-Treatment and Prognosis

Doctors and medical researchers are not completely sure how or why folic acid has such a positive impact on the prevention of neural tube defects, but do know the vitamin is crucial to DNA development. More research is needed to better understand how neural tube defects are caused and how they can be prevented entirely.