Neural Tube Defects (NTDs)
NTDs result from the failure of the neural tube to close during the 4th week of gestation. This leads to persistent connections between the amniotic cavity and the spinal canal or ventricular system.
| Defect | Key Characteristics |
|---|---|
| Anencephaly | Failure of the cranial neuropore to close. No forebrain/calvarium. Associated with polyhydramnios (fetus cannot swallow). |
| Spina Bifida Occulta | Failure of the bony spinal canal to close (vertebral arch defect). Typically asymptomatic; may have a tuft of hair or a skin dimple. |
| Meningocele | Protrusion of meninges through the vertebral defect. |
| Myelomeningocele | Protrusion of meninges and spinal cord tissue. Often associated with Chiari II malformation. |
High-Yield Clinical Markers:
- Screening: Elevated Alpha-fetoprotein (AFP) in amniotic fluid and maternal serum. Increased Acetylcholinesterase is a highly specific marker.
- Prevention: Maternal folate supplementation (at least 400 µg/day) starting before conception is the standard for prevention.