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# Trisomy 18 (Edwards) and trisomy 13 (Patau)

Trisomies 18 and 13 are serious chromosome disorders with major heart, brain and face defects. Most affected babies die in the first year.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Interventricular septum](https://durgical.com/en/anatomy/interventricular-septum/)
- [Soft palate](https://durgical.com/en/anatomy/soft-palate/)
- [Interatrial septum](https://durgical.com/en/anatomy/interatrial-septum/)
- [Aortic arch](https://durgical.com/en/anatomy/aortic-arch/)
- [Pulmonary trunk](https://durgical.com/en/anatomy/pulmonary-trunk/)
- [Frontal lobe](https://durgical.com/en/anatomy/superior-frontal-gyrus/)
- [Mandible](https://durgical.com/en/anatomy/mandible/)

## Why it happens

- [Chromosome abnormalities: number and structure](https://durgical.com/en/general-pathology/chromosome-abnormalities-number-and-structure/)
- [Trisomies 21, 18 and 13, and the 22q11.2 deletion](https://durgical.com/en/general-pathology/trisomies-21-18-and-13-and-the-22q11-2-deletion/)

## What it is

Two autosomal trisomies, usually caused by an extra full copy of chromosome 18 (Edwards syndrome) or chromosome 13 (Patau syndrome), that produce multiple severe malformations, profound intellectual disability and very short survival.

## Who gets it

Trisomy 18 occurs in about 1 in 5,000 live births and trisomy 13 in about 1 in 16,000; both are far more frequent in pregnancy because many affected fetuses miscarry or are stillborn. Risk rises with maternal age. They are, after Down syndrome, the most common autosomal trisomies seen at birth.

## Causes

- Meiotic nondisjunction, mostly maternal, producing a full extra chromosome (most cases)
- Robertsonian translocation, more relevant in trisomy 13 and sometimes inherited from a balanced carrier parent
- Mosaicism, with an extra chromosome in only some cells and usually milder features

## Risk factors

- Advanced maternal age
- Parent carrying a balanced translocation (translocation forms)
- Previous pregnancy with a trisomy

## Pathophysiology

The extra chromosome causes an imbalance in the dosage of many genes during early organ formation. In trisomy 18 this mainly affects growth, the heart, hands, jaw and [kidneys](https://durgical.com/en/anatomy/kidney/). In trisomy 13 it disrupts forebrain and midline facial development (holoprosencephaly, cleft lip and palate, eye defects), the heart and the limbs. Central apnoea and heart failure explain most early deaths.

## Classification

- Trisomy 18 (Edwards syndrome): full, mosaic or partial
- Trisomy 13 (Patau syndrome): full, translocation or mosaic

## Symptoms and signs

- Trisomy 18: intrauterine growth restriction, low birth weight and weak cry
- Trisomy 18: clenched fists with overlapping fingers, rocker-bottom feet, small jaw (micrognathia), prominent occiput and low-set ears
- Trisomy 18: short [sternum](https://durgical.com/en/anatomy/sternum/), horseshoe kidney and congenital heart defects (ventricular septal defect most common)
- Trisomy 13: holoprosencephaly, microcephaly and small or absent eyes (microphthalmia)
- Trisomy 13: cleft lip and palate, postaxial polydactyly and scalp [skin](https://durgical.com/en/anatomy/skin/) defects (cutis aplasia)
- Trisomy 13: congenital heart defects, omphalocele and polycystic kidneys
- Both: severe hypotonia or hypertonia, feeding difficulties and profound developmental delay

## Red flags

- Apnoea or cyanotic episodes
- Signs of heart failure: breathlessness, sweating with feeds, poor weight gain
- Aspiration and choking during feeds
- Seizures
- Severe dehydration or hypoglycaemia from feeding failure

## Diagnosis

**Clinical**
Suspected from the pattern of malformations at birth or on prenatal ultrasound; a family history of translocation or previous trisomy raises concern.

**Tests**
Prenatal screening with maternal serum markers or cell-free fetal DNA; confirmation by chorionic villus sampling or amniocentesis. After birth, karyotype confirms the trisomy and distinguishes translocation and mosaic forms (rapid FISH may be used first). Parental karyotype in translocation cases.

**Imaging**
Prenatal ultrasound may show growth restriction, heart defects, clenched hands, holoprosencephaly, polydactyly or omphalocele. After birth, echocardiography, cranial and renal ultrasound assess malformations.

## Differential diagnosis

- Down syndrome (trisomy 21)
- Pena-Shokeir sequence (fetal akinesia) for trisomy 18-like features
- Isolated holoprosencephaly or Meckel-Gruber syndrome for trisomy 13-like features
- Smith-Lemli-Opitz syndrome
- Other chromosomal deletions or duplications

## Goal of treatment

Plan care with the family, focused on comfort and quality of life, and decide case by case whether to offer intensive or surgical treatments, as some children survive longer with them.

## Treatment

**Conservative**
Individualised family-centred plan, often including palliative care: feeding support (tube feeding when needed), management of apnoea, infections and pain.

**Surgical**
Selected surgery in some children after discussion with the family, such as cardiac repair, gastrostomy or repair of omphalocele.

**Rehabilitation**
Physical, occupational and speech therapy for children who survive infancy.

**Follow-up**
Follow-up of heart, breathing, feeding, growth and seizures; genetic counselling for parents on recurrence risk.

## Complications

- Heart failure from congenital heart defects
- Central and obstructive apnoea
- Aspiration pneumonia and recurrent infections
- Feeding failure and poor growth
- Profound intellectual disability in survivors
- Stillbirth and miscarriage

## Prognosis

Very poor: many affected babies die before birth or in the first weeks, and only about 5 to 10% survive beyond the first year, with severe disability. Mosaic and partial forms can be milder.

## Prevention

- Prenatal screening and diagnosis allow informed decisions and planning of delivery and care
- Genetic counselling for parents with a balanced translocation or a previous affected pregnancy

## Test yourself

Think of the answer, then tap the question to see it.

## What is the most common cause of trisomy 18 and trisomy 13?

Meiotic nondisjunction, usually maternal, resulting in a full extra chromosome; risk rises with maternal age.

## Which hand finding is classic for trisomy 18?

Clenched fists with overlapping fingers (index over middle, fifth over fourth).

## Which brain malformation is typical of trisomy 13?

Holoprosencephaly, often with cleft lip and palate and eye defects such as microphthalmia.

## Which test confirms trisomy 18 or 13 after birth?

Karyotype, which also identifies translocation and mosaic forms.

## What is the approximate one-year survival in trisomy 18 and 13?

About 5 to 10%; most affected infants die in the first weeks or months.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/conditions/trisomy-18-and-trisomy-13/)

## Related conditions

- [Down syndrome (trisomy 21)](https://durgical.com/en/conditions/down-syndrome/)
- [Ventricular septal defect](https://durgical.com/en/conditions/ventricular-septal-defect/)
- [Atrial septal defect](https://durgical.com/en/conditions/atrial-septal-defect/)
- [Patent ductus arteriosus](https://durgical.com/en/conditions/patent-ductus-arteriosus/)
- [Cleft lip and palate](https://durgical.com/en/conditions/cleft-lip-and-palate/)
- [Gastroschisis and omphalocele](https://durgical.com/en/conditions/gastroschisis-and-omphalocele/)
- [Spina bifida (myelomeningocele)](https://durgical.com/en/conditions/spina-bifida/)
- [Fetal growth restriction](https://durgical.com/en/conditions/fetal-growth-restriction/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Trisomy 18](https://medlineplus.gov/genetics/condition/trisomy-18/) (MedlinePlus Genetics (U.S. National Library of Medicine), 2024); [Trisomy 13](https://medlineplus.gov/genetics/condition/trisomy-13/) (MedlinePlus Genetics (U.S. National Library of Medicine), 2024).

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Source: https://durgical.com/en/conditions/trisomy-18-and-trisomy-13/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/trisomy-18-and-trisomy-13/