Developmental Age Assessment
Based on the developmental milestones described, this infant is approximately 12 weeks (3 months) old, making the answer C) 12 weeks.
Key Milestone Analysis
The three developmental achievements presented align precisely with the 3-month developmental stage according to established pediatric guidelines:
Visual Tracking (180-degree object following)
- 180-degree visual tracking is a hallmark of 3-4 month development 1
- At 4 months, infants demonstrate mature smooth pursuit eye movements and can predict where occluded moving objects will reappear 2
- Visual tracking at this age requires sustained attention and prediction of object trajectory 3
Motor Development (No head lag on pull-to-sit)
- Pull to sit with no head lag occurs at an average age of 3.0 months 1
- This milestone reflects appropriate muscle tone development 1
- Head lag at 6 months would be concerning and associated with developmental disruption 4, but absence of head lag at 3 months is expected
- The milestone "head steady in sitting" occurs earlier at 2.0 months on average 1
Social Development (Social smiling)
- Social smiling in response to face and voice emerges at an average age of 1.5 months 1
- By 3 months, this behavior is well-established and the infant becomes a more active social participant 1
- The presence of social smiling indicates normal social-emotional reciprocity development 5
Developmental Context
The combination of all three milestones points specifically to 3 months (12 weeks) because:
- At 4 weeks: Infants would not yet demonstrate 180-degree tracking or reliable no head lag 1
- At 8 weeks: Head control is improving but 180-degree tracking is not yet fully developed 1
- At 12 weeks: All three milestones converge as expected achievements 1
- At 16 weeks: These would be considered delayed milestones, and additional skills (reaching for objects at 4.0 months, asymmetric tonic neck reflex gone at 4.0 months) would be expected 1
Clinical Pitfall to Avoid
Do not confuse "head steady in sitting" (2 months) with "pull to sit, no head lag" (3 months)—these are distinct milestones assessed differently 1. The former tests passive head control while supported, while the latter tests active neck flexor strength during the pull-to-sit maneuver.