Infant developmental milestones – Neurological development is assessed in terms of the milestones i.e. maturation of certain physical functions e.g. sitting or smiling, which are expected to be achieved by a normal child within certain age limits. They may be broadly divided into 4 major fields —
1. Gross motor infant developmental milestones e.g. sitting, standing etc.
2. Fine motor or manipulative or adaptive milestones e.g. handling of objects, feeding himself etc.
3. Psychosocial milestones e.g. Interacting with family and friends, expression of emotions etc.
4. Linguistic milestones e.g. Development of speech.
Although the age of appearance for various infant developmental milestones significantly differs from child to child, a tentative timetable (± 2-3 months) for appearance of common milestones is shown in Table 2.7. it is re-emphasized that pin-pointing the precise age of appearance for a particular milestone is neither possible nor desirable, due to continuous maturation of these functions.
A) Gross motor infant developmental milestones require normal neurological development as well as adequate muscle mass and tone. Thus, these functions may be delayed in grossly malnourished children despite adequate neurological functions.
Neck (Head) holding may be considered as the first key gross motor milestone (3 months), which should be assessed in various positions for maturity and persistence.
Other important motor infant developmental milestones in infancy include – Roll-over from supine to prone position (4 months) and prone to supine position (5 months), Sitting with support (6 months) and without support (8 months), Crawling (9 months), Standing with support (10 months) and without support (12 months) and Walking (15 months) etc.
B) Fine motor infant developmental milestones are more reliable indicators of neurological maturity, as these functions are governed by large cerebral area and usually not affected in nutritional disorders. Isolated delay in maturation of these milestones indicate cerebral palsy or peripheral nerve injury e.g. Erb’s paralysis.
Important domains of fine motor development in order of maturity include — i) Eye coordination e.g. visual fixation, ii) Eye-hand coordination e.g. reaching- out for objects, iii) Hand coordination e.g. grasp maturity, iv) Hand-hand coordination e.g. transfer of objects, v) Hand-mouth coordination e.g. feeding himself.
Visualfixation to a moving object (4-6 weeks) may be considered as the earliest and easily identifiable fine motor milestone, which is tested by assessing infant’s eye movements in response to a bright moving object e.g. torch-light or a red-ring tied to a string.
Other important fine motor infant developmental milestones in infancy include – Voluntary grasp (4 months), Reach-out for an object (5 months), Transfer of object from one to other hand (6 months), Pincer-grasp (9 months, Fig. 2.4a), Release of an object on request (10 months) and Building of a tower of two cubes (12 months) etc.
C) Psychosocial infant developmental milestones i.e. development of interpersonal relationship and social skills, depend on higher cerebral functions as well as external inputs e.g. normal vision and social stimulation. Thus, isolated delay in these milestones indicates mental retardation, autism, visual impairment and emotionally deprived child e.g. orphans.
Social smile may be considered as the first important social milestone (6 weeks).
Other important psychosocial infant developmental milestones in infancy include – Recognition of mother (3 months), Laughing aloud (4 months), Stranger ‘sfear or anxiety (6 months), Waving bye-bye (9 months), Response to name call (9 months), Kissing on request (12 months) and playing with a ball (12 months). (See Table 2.7 for details)
Hand regard i.e. exploration or enjoying own hand- image is an important psychosocial milestone that appears at 3-4 months and disappears by 6 months. Persistence of hand regard beyond 6 months is strongly suggestive of delayed neurological development.
U) Linguistic infant developmental milestones require normal hearing, normal central functions as well as healthy organs of phonation. Hearing impairment is the commonest cause of delayed language development.
Although the startle response to a sudden sound is present in newborns suggestive of hearing ability, Turning the head towards the sound-source may be considered as the earliest linguistic milestone (6 weeks).
Other important linguistic infant developmental milestones in infancy include – Cooing sounds (4 months), Monosyllables e.g. ma, da (6 months), Bisyllables e.g. ma-ma, da-da (9 months), Response to verbal requests (12 months) and a Vocabulary of two words (12 months). Important aspects of language development are also discussed.
Toilet training is an important indicator of mature cerebral as well as autonomic control, which is usually achieved by 18 months for bowel movements, 24 month for day-time bladder control and 36 months for nighttime bladder control, though occasional bed-wetting is not uncommon till 5-6 years.