Developmental delay



Developmental delay broadly refers to children < 5 years old who fail to meet expected milestones.

Developmental delay is the failure to achieve developmental milestones in comparison to peers of the same age range. This is generally defined as being more than two standard deviations below the mean.

The core developmental milestone domains include:

  • Gross motor
  • Fine motor/vision
  • Speech/language
  • Social/emotional
  • Cognitive

Developmental delay is not a diagnosis. Instead, it is a descriptive term that requires further investigation into the possible cause of the delay. A delay may be isolated occurring in a single domain. When a significant delay occurs in ≥ 2 domains in a child < 5 years old, it is known as global developmental delay.

The delay in development may be short-term and overcome with the right support. Alternatively, the delay may be more significant and require lifelong support. A significant delay may indicate the child has a specific underlying developmental disorder or syndrome (e.g. learning disability or autism spectrum disorder).

For more information on milestones see our accompanying notes on Developmental milestones.


Several closely related terms are discussed in association with developmental delay (e.g. developmental disorder).

Most cases of developmental delay are idiopathic (no known cause) and time-limited. However, developmental delay may be the first feature of ‘progression’ towards a wider developmental problem. For example, delayed speech may indicate early progression to autism spectrum disorder or learning problems may indicate a learning disability.

Some key terms relating to developmental delay are discussed below.

Developmental arrest / regression

This is defined as a period where a child has a normal developmental phase, which is followed by a failure to develop new skills or even loss of previously acquired skills. Regression is a red flag that requires further assessment.

Developmental disorder

A developmental disorder (sometimes referred to as developmental disability) refers to a very large group of conditions or syndromes that occur in childhood and are characterised by developmental delay. They often have a typical sequence or pattern of development that enables their identification through specific testing. They may also be referred to more broadly as ‘neurodevelopment disorder’.

Learning disability

A learning disability refers to reduced intellectual ability that makes it hard to complete everyday activities of which the onset occurs during childhood. Learning disabilities make it harder for the child to learn and understand things compared to their peers.

It is broadly defined as:

  • Lower intellectual ability
  • Significant impairment of social or adaptive functioning
  • Onset in childhood

It is broadly categorised into mild, moderate, severe and profound based on IQ.

Learning difficulty

A learning difficulty refers to a specific problem where the person has difficulty in one area (e.g. reading, writing). These types of difficulties do not affect intellectual ability.

Neurodevelopmental disorder

Neurodevelopmental disorders are a large group of conditions that start in the developmental period (i.e. childhood), causing deficits in development and impairment in normal functioning. They are commonly associated with learning disabilities. Key examples of neurodevelopment disorders include:

  • Autism spectrum disorder
  • Attention deficit hyperactivity disorder
  • Feeding and eating disorders
  • Movement disorders (e.g. Tics)


In children < 5 year old, developmental delays is reported in 10-15%.

Developmental delay is reported to occur in 10-15% of children with global developmental delay seen in 1-3%. In addition, an estimated 2.5% of children in the UK have a learning disability.


A vast number of causes may lead to developmental delay.

Multiple causes may contribute to developmental delay. Often, a specific cause for the delay in development cannot be identified (i.e. it is idiopathic).

Causes of development delay can be broadly divided into four categories:

  • Antenatal
  • Perinatal
  • Postnatal
  • Other


This refers to problems that may occur during the pregnancy.

  • Genetic disorders: Down syndrome, Fragile X syndrome, Chromosomal abnormalities
  • Structural brain disorders: microcephaly, absent corpus callosum, hydrocephalus
  • Vascular: occlusion, haemorrhage
  • Infections: rubella, toxoplasmosis, cytomegalovirus
  • Drugs & toxins: alcohol, smoking, anti-epileptics


This refers to problems that may occur around the time of birth.

  • Prematurity
  • Intrauterine growth restriction
  • Intraventricular haemorrhage
  • Perinatal asphyxia (i.e. hypoxic-ischaemic encephalopathy)
  • Hypoglycaemia


This refers to problems that may occur following birth.

  • Anoxia: suffocation, near-drowning, seizures
  • Trauma
  • Malnutrition
  • Infections: meningitis, encephalitis
  • Metabolic: electrolyte disturbances, hypoglycaemia


Many other causes may lead to developmental delay. These can include:

  • Severe understimulation
  • Maltreatment
  • Malnutrition
  • Maternal mental health disorder

Suspecting developmental delay

Children in the UK should be offered routine developmental screening assessments.

The are several ways in which a child may be identified as having developmental delay. These include:

  • Routine developmental screening
  • Parental concern
  • Caregiver or teacher concerns

Developmental screening

In the UK, shortly before or after a baby is born, the parents will be given a child health record known as the ‘red book’. This is important to document key things about the child’s health (e.g. weight, height, vaccinations) and development.

The child will have several reviews by a health visitor, or another healthcare professional, to ensure a baby is growing and developing at the appropriate stages. The key assessments that specifically relate to the assessment of developmental are listed below:

  • 6-8 weeks: a thorough physical examination of the child
  • 9-12 months: assessment of language and learning, safety, diet, and behaviour. Often asked to fill in an ‘ages and stages questionnaire’ known as ASQ-3
  • 24-30 months: second health development review. Important to assess general development including movement, speech, social skills and behaviour, and hearing and vision. Another ASQ-3 questionnaire will be asked to be filled out.

Parental, caregiver, or teacher concerns

Outside of usual developmental assessment visits, concerns raised about a child's development should be taken seriously and a clinical assessment completed including a thorough history and examination. If developmental delay is identified, patients can be referred for formal specialist assessment.

Assessment and diagnosis

A comprehensive clinical assessment is the key to identifying developmental delay.

The initial history and clinical examination are important to guide further investigations and the appropriate referral for specialist assessment by a paediatrician, psychologist, and/or psychiatrist.

When a specific diagnosis is not suspected on history and examination a step-wise approach to investigations should be completed. This usually focuses on investigations for a genetic or metabolic causes of developmental delay.

It is estimated that 1/3rd of causes are established through history and examination, 1/3rd through clinical assessment that prompts a specific investigation, and 1/3rd by investigations alone.


Developmental milestones are essentially age-specific tasks that most children should be able to complete by a certain age. They can be divided into specific domains. It is a delay in these milestones, across one or more domains, that helps identify developmental delay. These milestones should be assessed during the history and examination of a child.

For more information on specific milestones see our notes on Developmental milestones.


A comprehensive history should be taken from the parents to elicit the developmental history of the child and any issues during the antenatal, perinatal, or postnatal period. This includes thorough family history, nutritional history, past medical history including any significant neonatal problems, immunisation history, and overall development.

Screening questionnaires can be used to help gather information including the ‘ages and stages questionnaire’ (ASQ-3).


A full head-to-toe examination should be completed that includes plotting the child’s height, weight, and occipitofrontal circumference as appropriate. All the clinical developmental milestones domains should be assessed including hearing and vision assessments. This will usually involve a well-validated assessment tool such as the Bayley Scales Of Infant and Toddler Development.

It may be more appropriate for a child to be referred for a comprehensive assessment by a specialist, particularly when developmental regression is seen.

First-line investigations

A variety of investigations may be requested depending on the suspected cause of developmental delay. In general, genetic tests form the basis of first-line investigations.

  • Genetic testing: Chromosome microarray, karyotype, Fragile X testing
  • Standard blood tests: Thyroid function, creatine kinase, full blood count, ferritin, urate, chloride, urea & electrolytes, calcium, liver function tests
  • Additional blood tests: lead poisoning, biotinidase deficiency
  • TORCH screen: tests to exclude Toxoplasma, Others (HBV, HIV), Rubella, CMV, and Herpesvirus if indicated

Second-line investigations

A whole plethora of second-line investigations can be completed depending on the suspected cause. It is important to assess and test for inborn errors of metabolism that are potentially treatable conditions if recognised.

  • Genetic disorder: more detailed tests (e.g. exome sequencing) can be completed if appropriate (usually requires assessment by a clinical geneticist)
  • Metabolic disorder: a variety of tests can be done to look for inborn errors in metabolism (e.g. plasma amino acids, acylcarnitine, urine organic acid, glycosaminoglycans, purines, and pyrimidines).
  • Structural problem: neuroimaging can be completed to assess the brain (e.g. MRI brain). A lumbar puncture may be completed in some cases to assess the cerebrospinal fluid.
  • Electrical disorder: electroencephalogram can be completed if epilepsy is suspected


Management of developmental delay requires input from the wider multidisciplinary team.

Due to the vast number of causes of developmental delay, management options are extensive and largely depend on the underlying domain affected and the cause of delay. For example, the management of muscular dystrophy causing a delay in motor skills will be very different from the management of autism spectrum disorder causing a delay in social and language skills.

A large number of healthcare professionals may be involved in the care of a child with developmental delay including:

  • Paediatrician
  • Neurologist
  • Psychiatrist
  • Speech and language specialist
  • Psychologist
  • Occupational therapist
  • Physical therapist
  • General practitioner
  • Many others

Once an underlying cause has been confirmed, children should be referred to the appropriate specialists. This may include a metabolic or genetic specialist for example. Counseling is important for children and their families.

Last updated: June 2022
Author The Pulsenotes Team A dedicated team of UK doctors who want to make learning medicine beautifully simple.

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