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The third month is a period of rapid development, as the infant makes the transition from the newborn period to a stage where he/she is fully adapted to extra-uterine life. 

The infant's social skills are developing fast: the baby is more alert and aware of his environment and has started to vocalise and take great pleasure in face-to-face interactions with those around him.

Vision, visual regard and reaching become much more functional and goal directed. The baby swipes at toys within reach, is starting to open his hands and actively explore objects placed within reach. He brings the hands together in the mid-line and to the mouth.

In supine he is starting to show more symmetry and has started to reach for toys, bring the hands together and to the mouth. The spontaneous movements of the arms and legs are probably an important stimulus to developing postural stability in supine.

He is an active kicker: the range of his movements is still constrained by the limited extensibility of the hip and knee structures that limit extension, and as a result the feet are often lifted off the supporting surface. 

Experience with being lifted and carried has provided lots and varied opportunities to practise holding the head erect and controlling the trunk against gravity and the baby has started to develop more effective postural responses to being moved.

Observation of spontaneous movements in the alert state continue to provide a window into the maturation of the brain. General movements are still seen, but increasingly to baby also displays fidgety movements.

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Third month: supine

Bly makes the following observations about posture and movement in supine.

Head and upper limbs

• The head is is held in the midline more often than before and the infant is begining the flex the head and tuck in the chin
  
• The upper limbs continue to be responsive to head position – with head more often in the mid-line, the arms are more often seen in a symmetrical position. The hands are often brought together in the midline.  
• The upper limbs are often positioned away from the body with the elbows extended – the infant appears to use the arms to stabilise the body in the midline.

Lower limbs 

• The feet are still held off the supporting surface (SS), but occasionally  the feet contact the SS
• If the one foot contacts the SS, the weight is shifted to the opposite side
• In the resting position the hips are still held in flexion, abduction, lateral rotation. The feet may come together invoking foot-to-foot play
• Active knee extension stretches the tight hamstrings resulting in less hip flexion and abduction.
• Active knee extension also stretches the gastrocnemius  leading to foot plantar flexion.

Third month:  prone

Bly makes the following observations regarding the posture and movements of the prone infant in the third month.

• The baby is able to support himself on the arms and hold the head up at a 45-90 degree angle in the midline
• There is increased extension in the thoracic and lumbar spine and the pelvis is lowered as the hips are less flexed than at 2 months.
• Head rotation to the side causes weight shift to the face side. The baby may roll to the side if weight shift is enough.
• The elbows are in line or in front of the shoulders and the weight is borne on the elbows and forearms  The shoulders assume a more flexed, adducted and externally rotated position than before – and this seems to pull the scapulae into protraction. Bly notes that there is winging of the scapulae which is an indication that the stabilisation action of the serratus anterior is not effective.
• The forearms are pronated and the wrist slightly extended. The fingers alternate between being loosely flexed and open – the baby may make scratching action on the surface especially at the sight of a toy.
• The position of the shoulders allows the chest to be lifted higher than before and weight is shifted caudally.
• The lower limbs  are usually symmetrical. The hips are still flexed and externally rotated, but less so than before.
• The ankles have become more mobile and move between flexion and extension.
• Flexion of the hips this position destabilises the infant – the weight shifts forwards and the baby collapses on the arms.
• One hip may flex – causing lateral weight shift but this is rare at 3 months

The third month: sitting

Bly describes sitting skills in the third month as follows:

• The infant has gained better control of the head, and has started to extend the trunk: he requires less support than before.
• The pelvis remains perpendicular to the support surface and the weight is carried by the ischial tuberosities.
• The infant may use shoulder abduction with scapula retraction to reinforce trunk extension – the upper extremities are yoked to the postural system
• The ability to effectively balance the trunk on the lower limbs has not yet developed. If support is removed the baby topples forwards – but by this stage the baby has developed some head righting – and he will extend the neck and thoracic spine, and abduct the shoudler blades to support this extension.
• As the hip adductors stretch, the thighs move closer to the supporting surface.

Third month: visual regard, reaching and hand use

The infant is able to converge on objects as near as 3” from the eyes.

The infant's ability to accommodate is fast approaching adult abilities though the range of accurate focus is smaller (5-20” and the ability to adapt to rapid changes in stimulus distances is slower. (White et al.)

Sustained hand regard is still common (White et al)

If an object is brought into reaching distance, the infant will fixate on it and swipe at or reach towards it. The infant shifts his gaze between the object and the hand repeatedly (White et al) .

If the object is presented to the side, the infant may swipe with one hand, or later with two hands turning the trunk as he does this. The success of these swiping actions depends on the child's general level of experience with reaching for toys and the tendency to actively explore

If an object is presented in the mid-line the infant is more likely to reach with both hands.

The baby's success at contacting a toy is improved when some postural support is provided.

The baby starts to explore with the hand whatever it touches – mouthing of the hands becomes more common.

The infant also brings the hands together in the midline, making contact between the hands and bringing them to the mouth followed by active mouthing.

Watching Will: being moved and changing position

Young infants get lifted, moved, carried and held as their carers care for and play with them.

This movement through space and experience of being supported different ways provides a rich variety of inputs for the visual and postural systems.

Being carried from place to place and being tipped and turned stimulates the vestibular system along with the visual system and is important in developing the interaction between these systems for stabilising the head in space.

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His ability to extend his head and upper trunk when he is tipped forwards is much more reliable than movement in the opposite direction.  He will lift his head in response to being tipped back – but the response is slow and I move him back quite cautiously.

Carers quickly learn to adapt their handling to the active responses of the baby. Will is a strong little fellow and does not mind being moved – he and I are confident in his ability to keep his head and trunk steady.

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