Neural tube defects are a group of congenital defects of the brain, spine, or spinal cord which occur when the structures fail to close during early fetal development. The estimated incidence rate of neural tube defects is between .5 and 1 in 1,000 pregnancies. Neural tube defects occur more frequently in females than males, and not all neural tube defects are fatal.
80% of neural tube defects can be accurately detected prenatally through maternal serum screening during pregnancy. Neural tube defects can be classified as open or closed. Closed neural tube defects only affect the spinal cord, and they do not have exposed brain tissue. Closed neural tube defects do not leak cerebrospinal fluid. Closed neural tube defects have a better prognosis than open neural tube defects.
Open neural tube defects occur when the neural tube fails to develop properly early in fetal development. Open neural tube defects have poorer prognoses and can be fatal. Conditions that are considered open neural tube defects include anencephaly, encephalocele, hydranencephaly, and myelomeningocele, which is a form of spina bifida.
The cause of neural tube defects varies widely and is not always known, but there are several factors that can increase the risk of neural tube defects: low levels of folate, maternal diabetes, maternal heart disease, maternal lung disease, and the maternal use of certain medications. Maternal pre-pregnancy obesity and a short interval between the end of a prior pregnancy and the current pregnancy also carry an associated increased risk for neural tube defects.
Maternal variations in the methylenetetrahydrofolate reductase (MTHFR) gene carry an increased risk for neural tube defects as this gene is instrumental for the production of the circulating form of folate, and a lack of maternal folate is linked to neural tube defects.
The recurrence risk for neural tube defects depends on the underlying cause. Genetic counseling is recommended prior to subsequent pregnancies.