Neural tube defects
Neural tube defect (NTD) refers to the incomplete closure of the neural tube in very early pregnancy.
The neural tube comprises of a bundle of nerve sheath which closes to form brain at the anterior end and spinal cord at the posterior end. The closure should occur at around the 28th day of conception failing which brain or spinal cord doesn't form properly.
Most common form of neural tube defects are:
Spina bifida can involve the spine, brain and/or meninges while anencephaly is an absence of cranial bones.
Other rare types include:
Neural tube defects affect approximately >1-11 out of 1000 4 pregnancies with spina bifida and anencephaly accounting for 95% of these reference required.
Folic acid deficiency is one of the leading causes of anencephaly. By supplementing with folic acid in early pregnancy, this defect can be prevented. It is more prevalent in developing countries and in mothers of low socio-economic status.
- maternal diabetes
- elevated maternal serum alpha-fetoprotein (MSAFP) levels
- elevated amniotic fluid acetylcholinesterase (AChE) levels: in an open neural tube defect 3
These are different for each entity and best discussed under each subtype.
Most neural tube defects can be diagnosed by one of the following tests:
- maternal serum alpha-fetoprotein (MSAFP): a screening test performed in the pregnant woman serum during 16-18 weeks of pregnancy (elevated)
- amniocentesis: invasive procedure, performed during 15 weeks of pregnancy
- antenatal ultrasound: allows detection of anencephaly/acrania at 12 weeks of pregnancy
Treatment and prognosis
Both the management and prognosis is heavily dependent on the type of neural tube defect. The risk for a subsequent pregnancy is thought to be ~5-10%.