Appendix B: Folic Acid and the Prevention of Neural Tube Defects
Neural Tube Defects
Neural tube defects (spina bifida, anencephaly and encephalocoele) are a major group of
serious birth defects.
The abnormality occurs when the spinal cord and brain are forming during the fourth week after conception (in the sixth week after the last normal menstrual period).
Over 95% of neural tube defect cases are born into families which have had an affected baby. The total prevalence of neural tube defects (NTDs) is 1 in every 500 babies in South Australia. This figure is similar in other states of Australia. There has been no upward or downward trend since 1966. There are about 40 cases each year in South Australia, 20 of which are spina bifida.
While the total prevalence of NTDs in South Australia has remained stable, prenatal diagnosis and termination of pregnancy has resulted in an 84% fall in birth prevalence during 1966-1991.
In South Australia tests before 28 weeks can detect 85% of NTD affected pregnancies.
Folic Acid is one of the B group vitamins and has an essential role in the very early development of the human nervous system.
Good sources of dietary folic acid are green vegetables, wholegrain breads and cereals, nuts, dried beans, peas and lentils and some fruits such as oranges, bananas and strawberries.
Folic acid is the name for standard pharmaceutical preparation. The different forms, which occur naturally in food, are collectively called folate.
Neural Tube Defects and Folic Acid
Prevention of the occurrence of NTDs is the ideal and research has shown that up to 70% of NTDs can be prevented by taking folic acid around the time that you plan to become pregnant.
Supplementation needs to begin before conception for it to be effective. It is recommended that you start increasing your folic acid intake one month before you intend to become pregnant and continue it until you are three months pregnant. Usually supplementation involves taking a tablet to ensure adequate intake.
There is no evidence that other vitamins or minerals will reduce your chance of having a baby with a NTD. There is no evidence that folic acid is effective in preventing a NTD if a woman starts taking it after she has become pregnant.
There is almost certainly more than one cause for NTDs. Taking folic acid around the time that you intend to become pregnant cannot prevent all cases of neural tube defects.
Groups with Increased Risk of Neural Tube Defects
Couples who have had a child with a neural tube defect are at an increased risk of having a second affected child. The risk is approximately 1 in 30. You should receive genetic counselling and it is recommended that the woman should take a higher dose of folic acid (5 mg daily) before becoming pregnant. If prenatal diagnosis is an option, the available methods should be discussed.
Couples with a close family history of NTD, and individuals with spina bifida, also have an increased chance of having an affected child.
If you have epilepsy and are taking sodium valproate or carbamazepine, you are at an increased risk of having a baby with spina bifida. This risk is estimated to be about 1 in 100 for sodium valproate and probably also for carbamazepine. It is recommended that if you are taking
anticonvulsant medications that you should also take the higher dose (5 mg daily) of folic acid, following discussion with their doctor.
Health professionals, especially GPs, have a key role in helping to prepare women for conception.
All women of reproductive age, especially those planning a pregnancy, should be encouraged to increase their intake of folic acid, particularly one month before and during the first three months of pregnancy. This will greatly reduce a woman’s chance of having a baby with NTD (up to 70%).
For low risk women (those with no close family history of NTD), taking a daily low dose folic acid tablet (.04-0.5 mg/500 mcg) as a supplement to their normal diet will ensure a satisfactory intake of folic acid. Women who do not take folic acid supplements in tablet form can achieve similar daily folic acid intake by eating a diet enriched in folate foods, though many women will find the necessary changes in diet difficult to maintain.
Health professionals have an important role in helping to alleviate anxiety in those pregnant women who have not increased their intake of folic acid prior to conception. The very low individual risk of having a baby with a NTD should be stressed to these women. There could be potential benefit from folic acid supplementation (0.4-0.5 mg/day) to women whose pregnancies are diagnosed before six weeks of pregnancy. It is recommended that women continue to take 0.5mg folate (folic acid) per day during the first three months of pregnancy to help prevent neural tube defects.
Folic acid is generally regarded as non toxic to humans. There have been very few reported cases of adverse reactions from folic acid. Toxicity has only been reported with high doses of folic acid (15 mg daily).
If you have the vitamin B12 deficiency (pernicious anaemia) you will need to discuss your specific requirements with your doctor.
Availability of Folic Acid
All pharmacies will stock at least one brand of folic acid. Purchase does not require a prescription. Customers may have to ask for the folic acid as it is sometimes held in the dispensary. No one brand is recommended over another.
Multi vitamin preparations rarely contain the recommended 500 mcg of folic acid
and women will generally require a specific folic acid preparation. Check the label if
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