Folic Acid Supplementation in Prevention of Neural Tube Defects

Neural tube defects (NTDs) are congenital anomalies (CAs) of the central nervous system. They are the most common birth defects along with congenital heart anomalies (CHAs) and anomalies of urinary system. EUROCAT (European Surveillance of Congenital Anomalies) reported that a total prevalence of major congenital anomalies was 23.9 per 1000 births in the period 2003-2007. CHAs were the most common non-chromosomal subgroup (6.5/1000), followed by limb defects (3.8/1000), anomalies of urinary system (3.1/1000) and nervous system anomalies (2.3/1000).

CAs are a special category of human disorders due to their very early onset and defect condition. Therefore there is a limited chance for complete prevention of it. NTDs are the most frequent CAs of the central nervous system. However, this has been a great progress in the prevention of NTDs with periconceptional folic acid (FA) or FA containing multivitamins (MVs). NTDs is defined as a group of severe CAs of the central nervous system resulting from failure of the neural tube to close during neurulation between 20 and 28 days after conception. Wide world, the birth prevalence of NTDs (spina bifida and anencephaly) varies among different populations. In some areas, such as Northern China, the prevalence is very high (1/200).

The neurulation is major step in brain development, who involves the formation of the first well-defined neural structure (neural tube). The neural tube forms during the third week of gestation (20-28 day). The neurulation is the embryonic process that leads to the ultimate development of the neural tube. 

This process can be divided into two phases:

Primary neurulation (3–4 week): involves the formation of the brain and neural tube from the caudal region to the upper sacral level. This phase of neurulation is associated with open NTDs and result in conditions including anencephaly, myelomeningocele (open spina bifida) and craniorachischisis.

Secondary neurulation completes the distal sacral and coccygeal regions. Disruption of secondary neurulation results with skin covering lesion sites of the spinal cord structure such as asymptomatic spina bifida occulta and severe spinal cord tethering are classed as closed NTDs.