Neural Tube Defects

A 28-year-old primigravida from rural Maharashtra presents to the antenatal clinic at 16 weeks gestation. She has not taken any folic acid supplementation. Routine ultrasound shows a fetus with an open neural tube defect (spina bifida) at the lumbosacral region with exposed neural tissue. Maternal serum alpha-fetoprotein (AFP) is markedly elevated. What is the most appropriate immediate next step in management?

At which week of embryonic development does the neural tube normally close completely?

A 32-year-old woman from Delhi, who did not receive folic acid supplementation in the periconceptional period, delivers a male infant at 38 weeks. The newborn has a small, skin-covered bulge in the lumbosacral midline with normal lower limb motor and sensory function and normal sphincter control. Imaging shows a fluid-filled sac containing only meninges and cerebrospinal fluid, with the spinal cord in normal anatomical position. What is the embryological defect responsible for this condition?

Which feature best distinguishes anencephaly from spina bifida cystica in terms of embryological defect and clinical presentation?

At what gestational week does the posterior neuropore normally close, and which vitamin deficiency is most strongly associated with neural tube defects arising from failure at this stage?