NEURAL TUBE DEFECTS EPIDEMIOLOGY

EPIDEMIOLOGY
Several interesting characteristics in the epidemiology of neural tube defects are as follows:
• Significant ethnic differences in prevalence exist; people of Celtic origin having the highest rate of spina bifida.
• A female predominance exists, with females accounting for 60-70% of children affected.
• Significant differences in geographic distribution exist, with countries in the British Isles having a higher rate than Asian countries.

A worldwide decline in NTD births has been recognized over the past 3 decades. For example, in the United States, New England has seen the incidence of spina bifida drop from 2.31 per 1000 births during the 1930s to 0.77 per 1000 births during the 1960s.

Reasons for the dramatic drop are not completely clear; however, certain factors probably play a part. The decline in neonates with NTD paralleled the development of commonly used prenatal screening tests such as alpha-fetoprotein (AFP) and ultrasonography (US). Termination of pregnancy increased 50-fold in the British Isles after the introduction of prenatal screening. Termination of pregnancy probably accounted for a significant amount of the decline of NTD in the United States, as well. In Atlanta in the early 1990s, more than 30% of affected pregnancies were terminated based on prenatal test results. When analysis is complete, use of periconception folate in the United States will most likely impact the incidence of NTDs in the late part of the 20th century.

In September of 1992, the US Public Health Service made the following strong recommendation: All women of childbearing age in the United States who are capable of becoming pregnant should consume 0.4 mg folic acid per day for the purpose of reducing the risk of having a pregnancy affected with spina bifida and other neural tube defects. Because the effects of high intakes are not well known, but include complicating the diagnosis of vitamin B-12 deficiency, care should be taken to keep total consumption less than 1 mg per day, except under the supervision of a physician.

That statement and the abundance of scientific data available to the public have reinforced the observation that risk of delivering a child with an NTD decreases significantly with the ingestion of periconception folate.

Prevalence of NTDs such as anencephalus and spina bifida seems to be higher in people of Celtic descent, such as the Welsh, Irish, and Scotch. Their prevalence rate is significantly higher than prevalence rates of persons of Anglo-Saxon or Norman origin. In the United States, the highest rates of NTD are found in Boston in people of Irish descent. In contradistinction, Africans, African Americans, and Asians seem to have very low prevalence rates of NTD. Recurrence risk of giving birth to a second child with an NTD varies with incidence. Investigators found the risk of having an additional affected birth after an anencephalic or spina bifida birth to be approximately 10.4% in Belfast but only about 4.12% in London. The risk in the United States is 1-3%.

The sex difference in prevalence seems to be consistent in most studies. About 55-70% of NTDs occur in females. This female predominance is seen in both stillbirths and live births.