Spina bifida means 'split spine'. There are 33 vertebrae in the spine - if one or more of these don't form properly in early pregnancy, the nerves in the spine may be unprotected, leading to damage of the central nervous system.
This damage may cause mobility difficulties, bladder and bowel problems and, in more severe cases, paralysis below the affected part of the spine.
Disruption of the nervous system depends on how high up the spine the problem lies and how well the spinal cord below the defect works.
The cause of spina bifida is unknown, but it's thought to result from a combination of genetic and environmental factors.
Faults in the LPP1 gene have recently been identified as contributing to a severe form of the condition. A couple with an affected child has a one in 25 chance of another - and an affected person has a one in 25 risk of having an affected child.
In spina bifida occulta, which affects up to one in ten people, there may be visible signs of a dimple or small hair growth on the back. This is a mild form and rarely causes disability.
In spina bifida cystica there is a sac or cyst (like a blister) on the back, covered by a thin layer of skin. The sac contains tissues that cover the spinal cord, cerebrospinal fluid and sometimes even the nerves and tissues of the spinal cord itself.
Antenatal blood tests can indicate the condition during pregnancy and 90 per cent of cases are picked up during ultrasound scans.
If the defect is minor, usually no treatment is necessary. If the defect is more serious, then surgery to repair it is often performed.
In cases where hydrocephalus is present, surgery is sometimes necessary to drain the cerebrospinal fluid that builds up. Normally, this fluid would flow from the brain down the spinal column before being absorbed into the bloodstream, but if the spinal cord is damaged it can't escape.
Physiotherapy helps with mobility. Regular use of a urinary catheter may be needed if there are difficulties passing urine normally. Emotional support is important, and special teaching may be necessary.
Taking a folic acid supplement from at least one month before conception through to the end of the 12th week of pregnancy can reduce the risk of spina bifida by up to 70 per cent.
It's recommended that women of child-bearing age take a 400mcg supplement of folic acid every day, in addition to a dietary intake of 200mcg folic acid a day.