For each pregnancy I have documented my belly weekly, though I fell short by a few weeks in my second pregnancy. This is my 3rd pregnancy all the way up to birth! I used the website mixbook to easily put three pages together and then used a collage app to finish the compilation of the pages.
I think it's neat to see the belly grow in stages, especially because it goes by so fast yet it doesn't seem to grow as fast as the pictures suggest.