Developmental Milestones and Developmental Delay

Introduction

Child development is assessed across four domains, and a competent assessment considers each separately rather than forming a general impression. A child can be walking beautifully and have no words at all, and the pattern of which domains are affected is what points towards the diagnosis.

• Gross motor - posture, head control, sitting, standing, walking, running, balance
• Fine motor and vision - visual fixation and following, reaching, grasp, manipulation, drawing
• Speech, language and hearing - both expressive (what the child says) and receptive (what they understand), and hearing itself
• Social, emotional and behavioural - smiling, attachment, play, self-care and interaction with others

Development follows predictable principles. It proceeds cephalocaudally - head control before sitting, sitting before walking - and proximal to distal, with whole-arm reaching before a fine pincer grip. Generalised mass movements are progressively replaced by specific, controlled ones, and primitive reflexes are suppressed before the equivalent voluntary movement appears. The sequence of skills is highly consistent; the rate varies enormously between normal children.

Milestones are therefore useful only when you are clear which kind of age you are quoting. The median age is when 50% of children achieve the skill - useful for reassurance, useless for referral. The limit age is roughly two standard deviations beyond the mean, the age by which about 97.5% of children have the skill, and a child who has not reached it needs assessment. Learn the limit ages; they are the ones that change management.¹

Milestones by age

These are median ages. They are worth knowing in outline, but do not use them as thresholds for concern.

Limit ages and red flags

These are the numbers that matter clinically. A child who has not achieved the skill by the limit age should be referred for assessment - not observed for another six months.

Primitive reflexes and postural reactions

Primitive reflexes are brainstem-mediated and present from birth. They are suppressed as the cortex matures, and their persistence beyond the expected age indicates a failure of that cortical inhibition - most often cerebral palsy. Postural reactions run in the opposite direction: they are absent at birth and appear as motor control develops.

Patterns of developmental problems

Classifying the pattern narrows the differential far more efficiently than listing every cause of delay.

Assessment

Surveillance in the UK

Development is monitored through the Healthy Child Programme, which specifies universal contacts at which development is reviewed: the newborn examination, the 6-8 week check, a 1-year review, and a 2 to 2.5-year review, the last of which uses a structured parental questionnaire.⁴ Parents also record milestones in the personal child health record - the red book.⁶

History

• Pregnancy - infections, medication, alcohol, drugs, growth restriction
• Birth and neonatal period - gestation, birth weight, resuscitation, encephalopathy, seizures, jaundice, hypoglycaemia, admission to a neonatal unit
• Developmental history in all four domains, asking what the child can do now and when each earlier skill appeared
• Explicitly ask about regression - has the child ever been able to do something they can no longer do?
• Vision and hearing - newborn screening results, parental concerns, recurrent otitis media
• Family history - consanguinity, developmental problems, learning disability, deafness, and late walkers or talkers in the family
• Social history - housing, parental mental health, domestic abuse, substance misuse, involvement of children's social care, and how much interaction and language the child hears
• What the parent is actually worried about, in their own words

Examination

• Growth - plot weight, length or height and, critically, head circumference. Microcephaly and macrocephaly both narrow the differential sharply.
• Dysmorphic features, and comparison with parental appearance
• Neurological examination - tone, power, deep tendon reflexes, primitive reflexes, gait, and coordination
• Skin - café-au-lait macules and axillary freckling in neurofibromatosis, ash-leaf macules and shagreen patches in tuberous sclerosis
• Cardiovascular and abdominal examination, looking for a murmur or organomegaly
• Vision - red reflex, fixing and following, cover test for squint
• Hearing - and refer for formal audiology rather than relying on a bedside impression
• Observe the child playing, which reveals far more about social and fine motor development than any structured test

Investigations

There is no standard panel; testing is guided by the pattern and the examination.

• Formal audiology and orthoptic or ophthalmology assessment in almost every child with unexplained delay
• Chromosomal microarray as the first-line genetic test in global developmental delay, plus fragile X testing
• Creatine kinase in any boy with gross motor delay or late walking - a raised CK identifies Duchenne muscular dystrophy, and delayed diagnosis is common
• Thyroid function, FBC, ferritin, U&Es, LFTs, bone profile, and vitamin D
• MRI brain where there are focal neurological signs, microcephaly or macrocephaly, seizures or regression
• EEG if seizures or an epileptic encephalopathy are suspected
• Metabolic screen - plasma amino acids, urine organic acids, lactate, ammonia and very long chain fatty acids - particularly where there is regression
• Lead level where there is a plausible exposure

Management

Management is delivered by a child development service and is multidisciplinary from the outset. The aim is to maximise function and participation rather than to normalise the child.

• Community paediatrician to coordinate assessment, investigation and diagnosis
• Physiotherapy for gross motor difficulties, with orthotics and equipment as needed
• Occupational therapy for fine motor skills, self-care, seating and adaptations to the home
• Speech and language therapy for expressive and receptive language, and for feeding and swallowing where relevant
• Portage - structured home teaching for preschool children with additional needs
• Educational psychology and an Education, Health and Care plan where the child needs support beyond what a school ordinarily provides
• Clinical genetics for diagnosis, recurrence risk and family counselling
• Treat what is treatable - hearing aids or grommets for hearing loss, glasses for refractive error, thyroxine for hypothyroidism, and anticonvulsants for epilepsy
• Support the family - benefits advice, respite, charity and parent support groups, and attention to parental mental health
• Preterm infants have their own structured developmental follow-up pathway, using corrected age and with defined review points⁵

Prognosis

Outcome depends almost entirely on the underlying cause. Isolated late walking in an otherwise normal child - particularly the familial bottom-shuffler - resolves completely. Isolated speech delay from glue ear resolves once hearing is restored. Global delay from a chromosomal disorder is lifelong, though the trajectory of skills continues upwards throughout childhood with the right support.

Early identification matters because early intervention works, and because some causes are directly treatable. Congenital hypothyroidism, hearing impairment, refractive error, epilepsy and vitamin D deficiency are all found by looking, and all change the trajectory when treated.

The one situation where the prognosis is genuinely different is regression. Loss of skills means an active process, and the differential includes conditions that are progressive, treatable, or both. A child who was walking and talking at 18 months and is not at 2 years needs a referral that week, not a review in six months - and it is worth being unambiguous about that in an exam answer as well as in practice.