After about three months, the baby is little bigger than a jellybean. But baby will start rapidly growing and moving and forming from then on in.
I was almost three months pregnant when I found out, and when the nurse told me that's what size she was, all through the pregnancy, she was nicknamed Jellybean.
My girl is six now, and has many other nicknames, but when I saw this question it made me smile remembering back that far.
Have a great day.