Abnormal Development - Anencephaly

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LA00 Anencephaly or similar anomalies

The above  ICD-11 International Classification of Diseases code is from the next version update due for release in 2018. ICD-10 is the 10th revision, Australian Modification (ICD-10-AM) is currently in use in Australian hospitals for admitted patients.

ICD-10 Q00 Anencephaly and similar malformations

  • Q00.0 Anencephaly, Acephaly, Acrania, Amyelencephaly, Hemianencephaly, Hemicephaly
  • Q00.1 Craniorachischisis
  • Q00.2 Iniencephaly
About International Classification of Diseases  

The International Classification of Diseases (ICD) World Health Organization's classification used worldwide as the standard diagnostic tool for epidemiology, health management and clinical purposes. This includes the analysis of the general health situation of population groups and is used to monitor the incidence and prevalence of diseases and other health problems. Within this classification "congenital malformations, deformations and chromosomal abnormalities" are (Q00-Q99) but excludes "inborn errors of metabolism" (E70-E90).

ICD-10 - Neural

ICD-10 Links: XVII Congenital Malformations | System Tables | XVI Perinatal Period | XV Pregnancy Childbirth | Abnormal Development | Prenatal Diagnosis | Birth | Neonatal Diagnosis |  ICD-11 | Reports

External WHO Links: ICD-10 | ICD-11


Anencephaly Rates (USA Data)[1]

A neural tube defect, anencephaly is a failure of the neural tube to close cranially. Also called exencephaly or craniorachischisis. The fortification of foods with folate has led to an overall decrease in the rate of this abnormality, showing that, at least in some cases, there is an association with maternal diet during pregnancy. Neural tube defects were historically more associated with Female infants, though a 2015 USA study showed no sex association in their population.[2] In contrast, a recent 2018 study of Latin American countries, has demonstrated a Female association and a substantial decrease in this ratio following folate fortification.[3]

Links: Low Folic Acid and NTDs
Neural Links: ectoderm | neural | neural crest | ventricular | sensory | Stage 22 | gliogenesis | neural fetal | Medicine Lecture - Neural | Lecture - Ectoderm | Lecture - Neural Crest | Lab - Early Neural | neural abnormalities | folic acid | iodine deficiency | Fetal Alcohol Syndrome | neural postnatal | neural examination | Histology | Historic Neural | Category:Neural

Some Recent Findings

  • Neural tube defects: Sex ratio changes after fortification with folic acid[3] "Historically, neural tube defects (NTDs) have predominated in female infants but the reasons remain unclear. In South America, the pre- folic acid fortification (FAF) rates of NTDs were around 18/10,000 births for females and 12/10,000 births for males, with an estimated sex ratio (male/female) of 0.67. During the post-FAF period, unpublished routine reports have indicated changes in the sex ratio for these defects while some descriptive reports are controversial. To date and to our knowledge, however, no studies specifically focusing on these changes to test this hypothesis directly have been undertaken. The aim of this study was to analyze changes in the sex ratio of infants with NTDs after FAF in South American countries. MATERIALS AND METHODS: With a descriptive cross-sectional study design, 2,597 infants with isolated NTDs born between 1990 and 2013 in 3 countries participating in the Latin American Collaborative Study of Congenital Malformations (ECLAMC) network were included: (Chile N = 521 and Argentina N = 1,619 [with FAF policies]; Venezuela N = 457 [without FAF policies; used as control]; total births = 2,229,561). The differences-in-differences method and Poisson regressions were used to evaluate the sex ratio shift from female to male before vs. after FAF, and to assess whether these differences were related to the fortification. RESULTS AND CONCLUSIONS: In Chile and Argentina the prevalence of NTDs, particularly anencephaly and cervico-thoracic spina bifida, showed a greater reduction rate in females than in males after FAF, resulting in a change of the sex ratio of infants with NTDs. Some mechanisms possibly involved in this differential reduction are proposed which might be useful to identify the pathogenesis of NTDs as a whole and specifically of those susceptible to the protective effect of folic acid." Low Folic Acid and NTDs
More recent papers  
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Fetal Anencephaly
Spina bifida front.JPG ZAnencephaly.jpg
ventral view lateral view

Sex Ratios

Neural tube defects were historically more associated with Female infants, though a 2015 USA study showed no sex association in their population.[2] In contrast, a recent 2018 study of Latin American countries, has demonstrated a Female association and a substantial decrease in this ratio following folate fortification.[3]

Neural tube defects sex ratio graph 01.png

Sex ratio changes for NTD cases and total births in Chile, Argentina, and Venezuela (1990–2013).[3]

NTD: neural tube defect; FAF: folic acid fortification; M/F: male/female; Sex ratio (male/female) for neural tube defect cases (full blue line), sex ratio for total births (dashed red line). Sex ratios estimated by multivariate regression models adjusted by hospital.


Anencephaly ultrasound.jpg

Anencephaly in a fetus (GA week 18) from a diabetic mother. Ultrasound images (coronal) show a complete absence of the cranial vault and brain and enlarged orbits.[4]

Links: maternal diabetes

Historic Anencephaly

These drawings are from a 1921 study of a single embryonic anencephaly.[5]

These drawings are from a 1925 study of 57 cases of anencephaly.[6]

Dodds GS. and Deangelis E. An anencephalic human embryo 16.5 mm long. (1937) Anat. Rec. 67(4): 499-505.


  1. Mathews TJ. Trends in spina bifida and anencephalus in the United States, 1991-2005, National Vital Statistics System.
  2. 2.0 2.1 Michalski AM, Richardson SD, Browne ML, Carmichael SL, Canfield MA, VanZutphen AR, Anderka MT, Marshall EG & Druschel CM. (2015). Sex ratios among infants with birth defects, National Birth Defects Prevention Study, 1997-2009. Am. J. Med. Genet. A , 167A, 1071-81. PMID: 25711982 DOI.
  3. 3.0 3.1 3.2 3.3 Poletta FA, Rittler M, Saleme C, Campaña H, Gili JA, Pawluk MS, Gimenez LG, Cosentino VR, Castilla EE & López-Camelo JS. (2018). Neural tube defects: Sex ratio changes after fortification with folic acid. PLoS ONE , 13, e0193127. PMID: 29538416 DOI.
  4. Alorainy IA, Barlas NB & Al-Boukai AA. (2010). Pictorial Essay: Infants of diabetic mothers. Indian J Radiol Imaging , 20, 174-81. PMID: 21042439 DOI.
  5. Frazer JE. Report on an anencephalic embryo. (1921) J Anat. 56(1): 12-9. PMID 17103933
  6. Nañagas JC. A comparison of the growth of the body dimensions of anencephalic human fetuses with normal fetal growth as determined by graphic analysis and empirical formulae. (1925) American J. Anatomy. 455-494.


Journal of Pediatric Neurosciences - is official publication of the Indian Society for Pediatric Neurosurgery.

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Search term: Neural Development Abnormalities | Anencephaly | Hydrocephalus | Encephalocele | Holoprosencephaly | Autism

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Cite this page: Hill, M.A. (2024, February 28) Embryology Abnormal Development - Anencephaly. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Abnormal_Development_-_Anencephaly

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G