Embryology · Teratology and prenatal diagnosis
Malformation, disruption, deformation, sequence, syndrome, association !
- Topic
The words doctors use to classify a birth defect by how it arose: they are not synonyms and they change the outlook.
Updated 2026-11-01
What it is
Birth defects are classified by mechanism. A malformation is an intrinsic error while an organ forms; a disruption destroys something that had formed normally; a deformation is mechanical moulding of a normal part. Sequence, syndrome and association describe how several defects cluster, and they guide recurrence risk and the search for other anomalies.
Key facts
- Minor anomalies (small ears, pigmented spots) are clues: three or more sharply raise the chance of a major defect.
- Disruptions rarely recur in another pregnancy because they are not genetic.
- Deformations mostly affect the musculoskeletal system and may improve after birth.
- A dysplasia is abnormal organization of cells within a tissue (e.g. skeletal dysplasias).
- Potter sequence: renal agenesis, oligohydramnios, pulmonary hypoplasia, flattened face and limb deformities.
Types of birth defect
| Type | What happens | Example |
|---|---|---|
| Malformation | Intrinsic error during formation | Cleft lip and palate |
| Disruption | Destruction of normal tissue | Amputation by amniotic bands |
| Deformation | Mechanical force on a normal part | Clubfoot from oligohydramnios |
| Sequence | One initial defect triggers others | Potter; Pierre Robin |
| Syndrome | Several defects with one known cause | Trisomy 21 |
| Association | Defects that cluster without one cause | VACTERL |
| Dysplasia | Abnormal cell organization in a tissue | Skeletal dysplasias |
Clinical notes
- Naming the type changes counselling: a genetic syndrome can recur; an amniotic band disruption almost never does.
- When one VACTERL component is found, the others are sought (vertebrae, anus, heart, trachea and oesophagus, kidney, limbs).
- In Pierre Robin sequence micrognathia pushes the tongue back, blocks palatal closure and can obstruct the airway.
Test yourself
Think of the answer, then tap the question to see it.
How does a disruption differ from a malformation?
A malformation is an intrinsic error while the organ forms; a disruption destroys tissue that had formed normally, as with amniotic bands.
What is a sequence, and what is a classic example?
One initial defect that triggers others in a cascade; example: renal agenesis, oligohydramnios, pulmonary hypoplasia and deformities (Potter sequence).
Why is VACTERL called an association rather than a syndrome?
Its defects occur together more often than chance predicts, but no single common cause has been identified.
Related
- Principles of teratology: critical periods, dose and genotype
- Renal agenesis and the Potter sequence
- First-arch syndromes: Treacher Collins and Pierre Robin sequence
- Clubfoot (talipes equinovarus)
- Limb defects: amelia, meromelia, polydactyly and syndactyly
- Esophageal atresia and tracheoesophageal fistula
- Anorectal malformations (imperforate anus)
- Amniotic fluid: polyhydramnios and oligohydramnios
- Methotrexate and misoprostol
Related conditions
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Langman's Medical Embryology, 13th ed., ch. 9: Birth Defects and Prenatal Diagnosis (Wolters Kluwer, 2015); About Birth Defects (CDC, 2024).
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Representative model, for educational purposes only.