I go by all the 4s too...
I Have that book too. It's really good.:)
Your welcome. I got this information from a book called What To Expect When Your Expecting. It is a good book for first time moms or even for moms to just refresh on things
Really?!?! I thought all the 4s were another month.... 4,8,12,16,20, etc....
I'm glad you posted this to. I'm on baby #2 and was on top of it with my first... now I couldn't remember the break down.