A neural tube defect (NTD) refers to 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 posterior end. The closure should occur at around the 28th day of conception failing which brain or spinal cord doesn't form properly.
Spina bifida can involve the spine, brain and / or meninges while anencephaly is absence of cranial bones.
Other rare types include
Neural tube defects affect approximately 2 - 5 per 1000 pregnancies with spina bifida and anencephaly accounting for 95% of these reference required.
Folic acid deficiency is a major cause of anencephaly. By giving supplementation of 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 materal 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 sub type.
Most neural tube defects can be diagnosed by one of the following tests
- maternal serum alpha fetoprotien (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 %.
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- 1. Bock G. Neural tube defects. John Wiley & Sons. (1994) ISBN:0471941727. Read it at Google Books - Find it at Amazon
- 2. Merz E, Bahlmann F. Ultrasound in obstetrics and gynecology. Thieme Medical Publishers. (2005) ISBN:1588901475. Read it at Google Books - Find it at Amazon
- 3. Wald N, Cuckle H, Nanchahal K. Amniotic fluid acetylcholinesterase measurement in the prenatal diagnosis of open neural tube defects. Second report of the Collaborative Acetylcholinesterase Study. Prenat. Diagn. 1989;9 (12): 813-29. - Pubmed citation
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