Birth defects

About neural tube defects and their etiology

A neural tube defect (NTD) is a birth defect that occurs when the neural tube, the embryonic structure that grows into the brain and spine, fails to properly close around 28 days after conception. At this stage, the embryo is about 2-3 mm long. The neural tube begins as a tiny pancake of tissue, consisting of the neural groove, neural fold and neural crest. First, it folds inward. Then the tube fastens or zippers up. When the zipper does not close completely, a small hole is left, and an NTD is formed. As the fetus develops, the hole does not close. The exact place of the defect along the neural tube determines the type of NTD that develops. 

The most common NTDs are spina bifida and anencephaly. Spina bifida is a bony defect of the posterior vertebral arches with herniation of neural tissue and meninges that is either covered by skin (closed) or is not (open). There are several types of spina bifida. Generally, the higher the defect occurs on the spine and/or the larger the defect, the greater the disability. Anencephaly is the absence or almost complete absence of the brain and calvaria (skullcap). This condition is always fatal.

Around 95 percent of NTDs occur as an isolated defect of unknown etiology. How folic acid prevents NTDs is not well understood and is an area of active research. More recent studies are investigating if supplemental folic acid compensates for genetic variations in folate metabolism.

Risk factors for NTD-affected pregnancies 

Scientists do not know the exact etiology of NTDs, however, the risk factors associated with these defects are well-known. What we do know is that in North Carolina all women capable of becoming pregnant are at risk for an NTD-affected pregnancy. Other risk factors for NTDs include:

• English/Irish ancestry
• Hispanic ancestry 
• Low socioeconomic status 
• Diabetes 
• Obesity 
• Poor dietary habits 
• Use of medications that are folate antagonists, such as anti-convulsant medications (e.g., dilatin, phenytoin), metformin, sulfasalazine, triamterene and methotrexate

North Carolina's NTD problem 

North Carolina is located in a region of the country with historically high rates of NTDs. The exact reason for this disparity is not known. However, North Carolina has a high number of women with known NTD-risk factors: maternal diabetes and obesity, English/Irish or Hispanic ancestry, and lower socioeconomic status. 

Today we still have higher NTD rates than the national average. With the inception of grain fortification in 1998 and the dedication of public health interventions, NTD rates have declined in recent years. 

In North Carolina, approximately 200 pregnancies are affected by an NTD each year. Over half of these babies don’t survive due to miscarriage, termination or fetal death.

Source: Birth Defects Monitoring Program, NC State Center for Health Statistics

The costs of NTDs 

“The most profound change with respect to the societal costs of spina bifida over the past decade was the reduction in birth prevalence and subsequent cost probably due to fortification of foods with folic acid. In other words, this public health measure had a profound impact on the total cost to society of spina bifida than did changes in medical care technology.” 
- Waitzman, N.J., Romano, P.S., & Grosse, S.D. The half-life of cost-of-illness estimates: The case of spina bifida. University of Utah, 2004, unpublished.

The emotional and physical cost for families affected by NTDs is very high. Half of NTD pregnancies do not survive. Children born with spina bifida can have many medical complications from mild to severe, including paralysis of the legs, loss of bladder and bowel control, and learning disabilities. Nonetheless, many children with spina bifida grow up to lead successful and productive lives. 

According to a study examining the health care expenditures of people with spina bifida in 2002-2003, the average medical expenditures for people with spina bifida during their first year of life were approximately $50,000.² After infancy, average medical care expenditures per person with spina bifida during 2003 ranged from $15,000 to $16,000 annually.³ Additionally, children ages 1-17 with spina bifida had average medical expenditures 13 times greater than children without spina bifida. CDC economist Scott Grosse estimates the cost in the United States of lifetime care for a person with spina bifida, adjusting for inflation, is just over $1 million.⁴ Cost estimates can be greatly underestimated because it’s hard to get an estimate on all factors involved in the cost of one case of spina bifida.