My kids all have relatively small heads, but each jumped from around the 25th percentile to near the 50th very quickly during infancy. By the time my third one came along, I was able to predict it in her. They aren't remotely autistic.

On the other end, my daughter has humongous feet. She's also very tall (predictions from age 2 are minimum 5'10"). Her first 18 months or so were characterized by growth spurts punctuated by occasional brief non-growth-spurt periods. It was amazing.

V.