At 37 weeks , HC is generally 33-35 cm … 31.5 cm is small for 37 weeks
HC will increase 2 cm / month for first 3 months
So at 1 month .. expected HC is 33.5 cm
Weight is appropriate
But baby should be evaluated for rapid HC increase if measurement at birth and subsequent visits are accurate..
Next Steps
If vomiting , downward eyes, delayed milestones , get USG (head) done …
Health Tips
Monitor HC every 15-30 days with pediatrician