Overview of Congenital Neurologic Anomalies
Congenital brain anomalies usually cause severe neurologic deficits; some may be fatal.
Some of the most serious neurologic anomalies (eg, anencephaly [see Anencephaly], encephalocele [see Encephalocele], spina bifida [see Spina Bifida]) develop in the first 2 mo of gestation and represent defects in neural tube formation (dysraphism). Others, such as lissencephaly (see Malformed Cerebral Hemispheres : Lissencephaly), result from problems with neuronal migration (see Malformed Cerebral Hemispheres), which occurs between 9 wk and 24 wk of gestation. Hydranencephaly (see Porencephaly : Hydranencephaly) and porencephaly (see Porencephaly) are secondary to destructive processes that occur after the brain has formed. Some anomalies (eg, meningocele) are relatively benign.
Amniocentesis (see Procedures : Amniocentesis) and ultrasonography (see Procedures : Prenatal ultrasonography) permit accurate in utero detection of many malformations. Parents need psychologic support when a malformation is detected and also genetic counseling, because the risk of having a subsequent child with such a malformation is high.
Women who have had a fetus or infant with a neural tube defect are at high risk and should take folate (folic acid—see Folate) supplementation 4 mg (4000 mcg) po once/day beginning 3 mo before conception and continuing through the 1st trimester. Folate supplementation reduces the risk of neural tube defects in future pregnancies by 75%.
All women of childbearing age who have not had a fetus or infant with a neural tube defect should consume at least 400 mcg/day of folate through diet or by taking a supplement (some experts recommend 800 mcg/day to further reduce risk) and continue doing so through the 1st trimester. Although folate supplementation reduces the risk of having a child with a neural tube defect, risk reduction is less than in women who previously had a fetus or infant with a neural tube defect (ie, risk reduction is < 75%).