my bitch has recently given birth to a litter of pups. I have read in the 'Book of the Bitch' that the bitch usually eats the after birth but after each pup was delivered, my bitch kept cleaning herself therefore i could'nt see if she ate the after birth or if it is still inside. Unsure on how to tell if she has delivered them or not. Would appreciate any advice as i know this could lead to infection and dont want her to come to any danger.

Ask your Vet to check her.  It's important that none are retained.

I agree, get your vet to check her.