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Spina bifida
Spina bifida is caused by problems in the development of an embryo in the womb. It is known as a ‘neural tube defect’ as it results from the failure of the embryo’s neural tube to develop properly.
The neural tube forms in the first few weeks of pregnancy and eventually goes on to form the baby’s brain, spinal chord and their coverings. Spina bifida is when neural tube does not develop properly and this results in an incorrectly developed spine.
The features of spina bifida vary between individuals, but commonly the small bones that make up the spine (the vertebrae) have not formed fully and may have gaps in them. In severe cases, one or more vertebrae may be missing, exposing the spinal chord (part of the nervous system that transmits signals from the nerve endings to the brain).
Normally, the neural tube is fully closed between 26 and 28 days after the start of the pregnancy. Very rarely, the neural tube fails to close or tears after it has closed.
This can affect the foetus in several different ways. In the least serious form, known as spina bifida occulta, the condition is hidden and usually is discovered only on X ray or through scanning. This type actually affects up to 30% of the population, nearly all of whom never become aware of it.
In the next most serious type, the coverings of the cord (the meninges) pass back through the opening to form a cyst-like swelling called a meningocele.
In the most serious type, the spinal cord itself is exposed. This is called a myelomeningocele or spina bifida aperta.
Myelomeningocele is more common in females than in males. The condition affects white people more often than black and Asian people, and tends to run in families. If the first child has myelomeningocele, the risk for the second child rises to 5% . If two children have myelomeningocele, the risk for a third is 15%.
Taking folic acid supplements 1-3 months before conception and for the first 1-3 of pregnancy will reduce the risk of spina bifida by about 20%.
Neural tube development occurs at a very early stage in pregnancy. This means that it is too late to take supplementary folic acid after the pregnancy is discovered. For this reason, in 1998 the US government made it essential for folic acid to be added to all grain products (bread and pasta). The effect of this has been dramatic. Although these conditions remain, we now know that their incidence can be reduced.
