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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Four developmental domains: gross motor, fine motor and vision, speech and language, social and adaptive behaviour
- Global developmental delay: significant delay in 2+ domains — affects ~1–3% of children under 5
- Key milestones: social smile 6 weeks, head control 3–4 months, sitting unsupported 6–8 months, first words 12 months, walking 12–18 months, 2-word phrases by 2 years
- Red flag milestones: not smiling by 8 weeks, no head control by 4 months, not sitting by 9 months, not walking by 18 months, no words by 18 months, loss of previously acquired skills at any age
- Common causes: cerebral palsy, chromosomal abnormalities (Down, Fragile X), ASD, hearing/visual impairment, hypothyroidism, neglect
- Assessment: history (prenatal, perinatal, family), developmental assessment tools, hearing and vision tests, genetics, metabolic screen, neuroimaging
Overview
Developmental delay refers to a child failing to reach expected developmental milestones within the normal age range. It may be isolated to one domain (e.g. isolated speech and language delay — consider hearing loss, ASD) or global (two or more domains — suggests a more significant underlying cause). The four developmental domains are gross motor, fine motor/vision, speech/language, and social/behavioural. Assessment requires a structured approach considering biological, environmental, and genetic factors. Early identification enables early intervention, which improves outcomes.
Epidemiology
Global developmental delay affects approximately 1–3% of children under 5. Isolated speech and language delay is more common, affecting 5–8% of preschool children. Causes include genetic/chromosomal (Down syndrome, Fragile X, Angelman, Prader-Willi), brain injury (hypoxic-ischaemic encephalopathy, intraventricular haemorrhage), infections (congenital CMV, rubella, meningitis), metabolic (hypothyroidism, phenylketonuria), environmental (neglect, deprivation, fetal alcohol spectrum disorder), and neuromuscular conditions. In 40–50% of global developmental delay, no specific cause is identified.
Clinical Features
Symptoms
Not achieving milestones at expected ages — identified by parents, health visitors, or GPs
Parental concern about development — should always be taken seriously
Loss of previously acquired skills (developmental regression)
Not walking by 18 months
No words by 18 months or no 2-word phrases by 2 years
Not smiling by 8 weeks
Signs
Abnormal tone: hypotonia (Down syndrome, neuromuscular) or hypertonia (cerebral palsy)
Dysmorphic features (suggest chromosomal/genetic cause)
Microcephaly or macrocephaly
Absent or asymmetric primitive reflexes
Visual inattention or absent response to sound
Investigations
First-line
Developmental assessmentStructured assessment using standardised tools — Griffiths, Bayley, or Schedule of Growing Skills. Performed by community paediatrician or developmental team
Hearing testEssential in ALL children with speech and language delay — newborn hearing screen, audiology referral
Vision assessmentOrthoptic and ophthalmological assessment
Second-line
Blood testsTFTs (hypothyroidism), FBC, ferritin, lead level, metabolic screen (amino acids, organic acids), creatine kinase (neuromuscular disease)
Genetic testingChromosomal microarray (CMA) is first-line genetic test for unexplained GDD. Fragile X testing. Consider whole exome/genome sequencing
MRI brainIf global delay, abnormal neurology, microcephaly/macrocephaly, seizures, or regression — look for structural abnormalities
Specialist
EEGIf seizures suspected or developmental regression (consider epileptic encephalopathy)
Metabolic investigationsIf regression, consanguinity, organomegaly, or unexplained global delay — urine organic acids, plasma amino acids, ammonia, lactate
Management
NICE and community paediatric pathways1
Assessment and diagnosis
- Thorough history: pregnancy, birth, neonatal period, family history, social circumstances
- Structured developmental assessment across all four domains
- Hearing and vision assessment — mandatory for all children with developmental concerns
- Investigations as above guided by clinical findings
2
Early intervention
- Speech and language therapy for communication delay
- Physiotherapy and occupational therapy for motor delay
- Portage (home-based educational programme for preschool children)
- Educational psychology input for learning difficulties
3
Multidisciplinary team
- Community paediatrician coordinates care
- Input from SALT, OT, physiotherapy, educational psychology, social services as needed
- Education, Health and Care Plan (EHCP) for children requiring additional support in school
- Genetic counselling if heritable cause identified
Complications
- Educational underachievement: Without appropriate support
- Behavioural difficulties: Frustration, challenging behaviour
- Social isolation: Communication difficulties
- Parental and family stress: Support and signposting essential
- Missed underlying diagnosis: Some causes are treatable (hypothyroidism, hearing loss, phenylketonuria)
UKMLA Exam Tips
- 1Know the key milestones: social smile 6 wk, head control 3–4 mo, sit 6–8 mo, walk 12–18 mo, first words 12 mo, 2-word phrases 2 yr
- 2Developmental REGRESSION (loss of skills) is always pathological — think metabolic, neurodegenerative, epileptic encephalopathy
- 3Isolated speech delay: ALWAYS check hearing first
- 4Chromosomal microarray is the first-line genetic test for unexplained global developmental delay
- 5Hypotonia + developmental delay: think Down syndrome, Prader-Willi, spinal muscular atrophy, hypothyroidism
- 6Hand preference before 12 months is abnormal — suggests contralateral hemiplegia (cerebral palsy)
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