Aih, a few of my mum friends kena same thing actually, doc kata baby's head is proportionate but body measurements lagging behind, kan? This usually just means your baby might be on the smaller side at birth, tapi since the head growth is on track, it's actually a good sign. Best thing is to follow up closely with your doc at the next scan or appointment, they might want to monitor growth pattern and check placenta function, just to make sure baby's getting enough nutrients. Don't worry too much lah, banyak cases like yours yang keluar healthy babies, but definitely jangan skip any check-ups k.