Miriam's casebook - The importance of folic acid
Julie's first baby, Henry, was born 18 months ago and now she'd like to have a second child. She had a normal delivery with Henry and he was fine, apart from a brown hairy birthmark at the base of his spine. Her doctor explained that this kind of birthmark may be linked to spina bifida, but means nothing by itself. However, Julie is worried that she is at greater risk of having a child with spina bifida because of the birthmark.
Spina bifida and hydrocephalus
Julie has read about the connection between folic acid deficiency and neural tube defects (spina bifida and hydrocephalus) and knows that she should start taking folic acid supplements now in case she becomes pregnant, but doesn't like taking tablets, even vitamin supplements.
The medical definition of spina bifida is a defect in which part of one or more vertebrae fails to develop completely, leaving part of the spinal cord exposed. Spina bifida can happen anywhere in the spine but it's most common on the lower back. Spina bifida symptoms depend on the severity of the spinal cord exposure; there may be paralysis, incontinence, or hydrocephalus - swelling of the brain.
There are different degrees of spina bifida. In one type the only defect is that the bony arches behind the spinal cord fail to join. When the bone defect is more extensive there may be neural tube defects such as a meningocele with protrusion of the meninges (the membranes surrounding the spinal cord) or, more serious still, a myelocele with deformity of the spinal cord itself. In the developing embryo the skin, brain, the spinal cord, and nerves all arise from the same layer of cells. This is why a birthmark over the end of the embryonic neural tube may be the only sign of late closure of the fetal neural tube. Parents who've had one child with spina bifida are more at risk, but having a child with a hairy birthmark (sacral naevus) like Henry's does not mean there's any increased risk in the next pregnancy.
The spine and the vertebral column develop from a flat layer of cells whose edges come together to form a tube, which is the hollow cavity inside the spinal cord. The closure of the cord and the bones that surround it, the vertebrae, takes place very early in the development of an embryo, usually within four weeks of conception.
Reducing the risks of folic acid
Research has shown that a woman needs sufficiently high levels of folic acid in her blood for the neural tube to close normally. Mothers with low blood levels of folic acid have a higher risk of having a spina bifida baby.
There's something else, too: normally folic acid is removed from the blood quite quickly, but when you're pregnant the kidneys filter it out of the blood at four times the normal rate. So if you don't eat folic-acid-rich foods or take folic acid supplements regularly you can become relatively deficient in folic acid, and your levels may drop low enough to put your baby at risk. It's therefore vital for all pregnant women to keep the blood levels of folic acid high.
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