Abnormal Development - Unknown

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How and why do things go wrong in development?

These unknown causes may be caused by either or genetic or environmental, but we do not understand the mechanism. This forms a very large group of abnormalities that we as yet do not yet know how they occur, the relevance paradox.

Idiopathic - relating to or denoting any disease or condition which arises spontaneously or for which the cause is unknown.

There are many different ways that developmental abnormalities can occur the 3 major types are Genetic (inherited), Environmental (maternal) and Unknown (not determined) derived abnormalities. There are many developmental abnormalities today through determined research and clinical observation, that are known to be genetic or environmental that in the past would have been described as "unknown". Note that genetic and environmental effects can also interact and it is this and the group now classified as "unknown causes" that require further research to place them in one of the two other real categories.

The environmental factors that cause or lead to any of these abnormalities are described as teratogens, and as the world develops many new chemicals and drugs even with testing it is difficult to easily identify the likelihood that they may represent a teratogen.

Abnormality Links: abnormal development | abnormal genetic | abnormal environmental | Unknown | teratogens | ectopic pregnancy | cardiovascular abnormalities | coelom abnormalities | endocrine abnormalities | gastrointestinal abnormalities | genital abnormalities | head abnormalities | integumentary abnormalities | musculoskeletal abnormalities | limb abnormalities | neural abnormalities | neural crest abnormalities | placenta abnormalities | renal abnormalities | respiratory abnormalities | hearing abnormalities | vision abnormalities | twinning | Developmental Origins of Health and Disease |  ICD-11
Historic Embryology  
1915 Congenital Cardiac Disease | 1917 Frequency of Anomalies in Human Embryos | 1920 Hydatiform Degeneration Tubal Pregnancy | 1921 Anencephalic Embryo | 1921 Rat and Man | 1966 Congenital Malformations

Some Recent Findings

More recent papers  
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Search term: Congenital Abnormality

<pubmed limit=5>Congenital Abnormality</pubmed>

Prenatal Diagnosis

Prenatal diagnosis are the clinical tools used to determine both normal and abnormal development. There are a growing number of new diagnostic techniques that are being applied to human embryonic development. Tests that occur after birth are described in Neonatal Diagnosis.

Diagnosis Links: Prenatal Diagnosis | pregnancy test | amniocentesis | chorionic villus sampling | ultrasound | Alpha-Fetoprotein | Pregnancy-associated plasma protein-A | Fetal Blood Sampling | Magnetic Resonance Imaging | Computed Tomography | Non-Invasive Prenatal Testing | Fetal Cells in Maternal Blood | Preimplantation Genetic Screening | Comparative Genomic Hybridization | Genome Sequencing | Neonatal Diagnosis | Category:Prenatal Diagnosis | Fetal Surgery | Classification of Diseases | Category:Neonatal Diagnosis

| 2015 BGD Tutorial - Applied Embryology and Teratology


Australia - Top 10

Congenital Anomalies Australian Data 1981-92
Australian Data 1981-92
Congenital Anomalies in Australia 2002-2003  
Congenital anomalies in Australia 2002-2003[2] was published in 2008 as part a new revised series on 33 selected congenital anomalies also monitored internationally by the International Clearinghouse of Birth Defects Surveillance and Research.
  • Hypospadia is the most commonly reported condition at birth, but severity of the condition is not reported to the national data collection.
  • Trisomy 21 (Down’s syndrome) is the next most commonly reported condition at birth (11.1 per 10,000 births), but many affected pregnancies are detected early and managed by early termination. An estimated 63.6% of the fetuses diagnosed with trisomy 21 were managed by terminations of pregnancy or were fetal deaths. When terminations of pregnancy were included, the estimated rate for trisomy 21 was 26.3 per 10,000 pregnancies. Trisomy 21 was more common with advancing maternal age.
    • Other chromosomal abnormalities such as trisomy 13 and trisomy 18 also had a large proportion of fetal deaths or terminations of pregnancy and were more common in women aged 40 years or older.
  • Neural tube defects were diagnosed in about 4.2 per 10,000 births.
  • More males than females diagnosed with congenital anomalies for many of the reported conditions (e.g. hydrocephalus, most of the reported congenital heart diseases, oesophageal atresia and polycystic kidneys).
  • Anencephaly - younger women had a higher rate compared with older women, most of the women who gave birth to a baby with anencephaly (77.2%) were in the 20–34 years age group.
Links: Human Abnormal Development | Hypospadia | Trisomy 21 | Trisomy 13 Trisomy 18 | Neural Tube Defects | Folic Acid and Neural Tube Defects | Hydrocephalus | Cardiovascular Abnormalities | Polycystic Kidney Disease | Anencephaly | Australian Statistics | Reports
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External Links: AIHW Report Page | NPESU Report Page | International Clearinghouse of Birth Defects Surveillance and Research

The ten most frequently reported birth defects in Victoria between 2003-2004.

  1. Hypospadias
  2. Obstructive Defects of the Renal Pelvis or Obstructive Genitourinary Defects
  3. Ventricular Septal Defect
  4. Congenital Dislocated Hip
  5. Trisomy 21 or Down syndrome
  6. Hydrocephalus
  7. Cleft Palate
  8. Trisomy 18 or Edward Syndrome - multiple abnormalities of the heart, diaphragm, lungs, kidneys, ureters and palate 86% discontinued.
  9. Renal Agenesis/Dysgenesis - reduction in neonatal death and stillbirth since 1993 may be due to the more severe cases being identified in utero and being represented amongst the increased proportion of terminations (approximately 31%).
  10. Cleft Lip and Palate - occur with another defect in 33.7% of cases.

Links: ACAMS | Australian Statistics

USA - Selected

USA Statistics
USA Selected Abnormalities (CDC National estimates for 21 selected major birth defects 2004–2006)  
Birth Defects Cases per Births (1 in ...) Estimated Annual Number of Cases
anencephaly 4,859 859
spina bifida without anencephaly 2,858 1,460
encephalocele 12,235 341
Anophthalmia/microphthalmia 5,349 780
patent ductus arteriosus‎/common truncus 13,876 301
transposition of the great vessels 3,333 1,252
Tetralogy of Fallot 2,518 1,657
atrial septal defects/ventricular septal defects 2,122 1,966
hypoplastic left heart 4,344 960
cleft palate without cleft lip 1,574 2,651
cleft lip with and without cleft palate 940 4,437
Esophageal atresia/tracheoesophageal fistula 4,608 905
Rectal and large intestinal atresia/stenosis 2,138 1,952
Reduction deformity, upper limbs 2,869 1,454
Reduction deformity, lower limbs 5,949 701
gastroschisis 2,229 1,871
omphalocele 5,386 775
Diaphragmatic hernia 3,836 1,088
Trisomy 13 7,906 528
Trisomy 21 (Down syndrome) 691 6,037
Trisomy 18 3,762 1,109
Links: Human Abnormal Development | CDC Birth Defects - Data & Statistics | USA Statistics | Victoria 2004 | USA 2006 | Europe 2010

Links: USA Monitoring Programmes | USA Statistics


  1. <pubmed></pubmed>
  2. Abeywardana S & Sullivan EA 2008. Congenital anomalies in Australia 2002–2003. Birth anomalies series no. 3 Cat. no. PER 41. Sydney: AIHW National Perinatal Statistics Unit.



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Cite this page: Hill, M.A. (2024, June 21) Embryology Abnormal Development - Unknown. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Abnormal_Development_-_Unknown

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