Yep the best advice up above - do not put him on the birth certificate at all! Also, you should give the baby your surname, not his. You do not want to give this idiot anymore of a hold over you by having him on the birth certificate and/or his surname.
He has treated you shockingly bad and he isn't going to change no matter how much you try to get him to and hope that he does. I am not trying to be nasty in being so blunt so I apologise if it seems that way I just do not like seeing women going through this with the thought that if only they could get him to see etc then everything would be okay. As he knows full well what he is doing but that is him. He knows he is messing with your head and he will be enjoying it.
You need to concentrate on your pregnancy and focus on your growing baby. You do not need the stress from him and risk any of that possibly affecting the baby. Also little ones do not need this kind of turbulent situation in their lives with a so called father coming and going as and when he feels like it in the family home.
I know it is very tempting to send him messages but I wouldn't. If you need to get it out then you could type it out on the note section on your phone that way you're not feeding his ego by messaging him and also ending up hurt in the process and arguing starting etc. Definitely do not save as a draft text as it is so very easy to send by accident!
I know it so hard but you need to come to terms with being a single parent. If he suddenly becomes civil and able to talk to you properly then you could always send updates regarding the pregnancy but only if he asks otherwise he will likely paint you as the obsessed one who won't leave him alone and you also do not need to affected emotionally again by him if he doesn't respond or if he messages something nasty.
You do not need him there at the birth. You need support for you and he isn't it. Nor is he reliable. No matter what he says and no doubts attempts to make it all about him don't fall for it. Also scans and other appts I would go alone also.
Once baby is here Definitely apply for maintenance officially and don't go down the informal route as he will likely take the piss and mess about with that also and you don't need the added stress of that.
Enjoy your pregnancy and honestly please don't waste anymore time on him. You could also block his number in the meantime if he is messaging nastily or calls etc as you don't need it.