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.
Numerous types of neural tube defect are recognised including 5-6:
- myelomeningocoele (spina bifida) (50%)
- anencephaly (40%)
- encephalocoele (5%)
- tethered cord
- iniencephaly (rare)
Neural tube defects affect approximately >1-11 out of 1000 pregnancies 4-6.
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
- maternal obesity 7
- anti-epileptic use in pregnancy 8
- 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%.
- 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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- 6. McDonnell R, Delany V, O'Mahony MT et-al. Neural tube defects in the Republic of Ireland in 2009-11. J Public Health (Oxf). 2015;37 (1): 57-63. doi:10.1093/pubmed/fdu016 - Pubmed citation
- 7. Huang HY, Chen HL, Feng LP. Maternal obesity and the risk of neural tube defects in offspring: A meta-analysis. (2017) Obesity research & clinical practice. 11 (2): 188-197. doi:10.1016/j.orcp.2016.04.005 - Pubmed
- 8. Egen-Lappe V, Hasford J. Drug prescription in pregnancy: analysis of a large statutory sickness fund population. (2004) European journal of clinical pharmacology. 60 (9): 659-66. doi:10.1007/s00228-004-0817-1 - Pubmed
Congenital spinal abnormalities
- spinal dysraphism