Nutritional Diseases

CASE 5: Neural Tube Defect

Clinical History:

A 22-year-old primigravida has a normal prenatal course, though there is minimal fetal movement. Her baby is born at term and weighs 3220 gm. Apgar scores are 9 and 10 at 1 and 5 minutes. Following delivery, physical examination reveals that the infant has a 5 cm mid-thoracic meningomyelocele.

  1. How could the risk for this condition have been reduced?

  2. If the mother were to have supplemented her diet with folic acid prior to and during the pregnancy, the risk for neural tube defects could be reduced by half. The risk cannot be completely eliminated.

  3. What diagnostic test(s) during pregnancy could have suggested the presence of this problem?

  4. Such a defect allows a fetal substance, alpha-fetoprotein, to gain access to the amniotic fluid, from which it can diffuse in increased amounts via the placenta into maternal circulation. Normal adults do not normally have significant quantities of AFP circulating. Thus, an elevated maternal serum AFP (MSAFP) can suggest a fetal neural tube defect. It is not that easy a test to interpret, because the MSAFP normally rises during pregnancy. Thus, the interpretation of the test is predicated upon knowing the proper gestational age. The AFP can also be measured in amniotic fluid if an amniocentesis is performed.

    An ultrasound can also detect many neural tube defects. The best time to find congenital fetal anomalies by ultrasound is in the 15 to 20 week period.

  5. What are potential outcomes for fetuses with neural tube defects?

  6. The most common and least harmful condition is known as spina bifida occulta, in which there is a posterior defect, but it is not an open defect. A meningocele has the potential to be repaired without significant sequelae. A meningomyelocele is more severe, and the higher it is located, the more severe the defects (paralysis) or the more likely that a repair is not going to achieve much. Open defects carry a risk for infection. Anencephaly is not survivable.