What are Neural Tube Defects?
Defects of the brain and spinal cord are referred to as neural tube defects. The most common defects are spina bifida, where the spinal column does not close, and anencephaly with failure of brain development. This occurs in 1/1000 pregnancies or approximately 3000 births per year. Neural tube defect incidence can vary by region in the United States. The highest incidence occurs in the southeast portion of the country.
Is There a Way to Prevent NTD?
Investigators in many studies have shown that multivitamins containing folic acid can reduce the risk of NTD. Supplementation with folic acid can reduce the risk of NTD by 70% in women with no prior history of NTD and 50% in women that have had 1 previous pregnancy with NTD. However, not all NTD are related to folic acid but rather some may be related to genetic, immune factors, diabetes, or obesity.
What Foods are Good Sources of Folate?
Bread/rolls/crackers and other enriched grain products,legumes, leafy vegetables, liver, breakfast cereal, fruits and juices are all good sources of natural folate. Folic acid is a synthetic form of folate (vitamin B9) that is found in the multivitamins. Women of childbearing age should consume 400 mcg to 800 mcg of folic acid before conception and throughout the pregnancy. Women with a prior history of NTD should consume 4 mg daily. Generally, enriched grain products contain approximately 140 mcg folic acid per 100 g flour.
Overall, it has been found that less than 10% of women meet the daily requirement of 400 mcg of folate per day. Women on low carbohydrate diets and those with malabsorption syndromes are at increased risk of folate deficiency. In addition, certain medications prevent absorption of folate such as beta-blockers, calcium channel blockers, cimetidine, Bactrim (septra), and certain anti-seizure medications such as phenobarbital, phenytoin, tegretol, primidone, and valproic acid.
The availability of folate from natural sources varies depending upon the food source and the way that the food is cooked. Therefore, supplementation is used in pregnancy to increase the availability of this vitamin. The body is unable to synthesize this vitamin and depends upon ingestion. Being a water soluble vitamin, excess amounts get excreted in the urine and excess consumption presents no known risks.
What is the Mechanism by which Folate Reduces NTD?
The mechanism of action of folate reducing neural tube defects is unknown. Some cases are independent and some are part of a syndrome of multiple other genetic anomalies. NTDs tend to occur more frequently in women that have a family history and also in couples that have had a previous child with this disorder. The first 25 days of gestation are particularly important for ingestion of this vitamin since neural tube closure occurs from day 18 to day 26 of gestation. Therefore, preconception ingestion with adequate amounts of folate that the body stores is very important since the critical time for neural tube closure is so early.
Is Folate Important for Other Reasons in Pregnancy?
Folate is important for DNA synthesis, cell division, and amino acid metabolism. Folate is critical in the metabolism and reduction of homocysteine in the body which prevents cardiovascular disease. Folic acid is also believed to reduce the risk of cleft palate and other genitourinary anomalies.
Recommendations
Obstetricians and other health care providers of women in the reproductive age range should counsel their patients on the importance of folic acid supplementation during pregnancy. First prenatal visits commonly occur after closure of the neural tube so folic acid consumption should begin before conception and continue especially in the early stages of pregnancy. Proper counseling is especially critical in those patients with a previous history of NTD or a family history since recurrence risk is higher.
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