How do you know if a gooey alien is pregnant?

Well you don't really! At the back of the alien there is a weird bit... if it is pregnant the baby will come out of there!!

This is wrong, you see Aliens have this huge big weird bit on the back of its head/neck, It'll have a few rings there. Another sign is that the head might feel a tad harder, which tells there is a baby. I have alot of aliens and I am an expert so please use this one.