What's your relationship been like before OP?
As a cop I've heard "I don't want to get him in trouble" so many times, probably the most common thing when talking to women who have been assaulted and hurt by their partners and I understand, you love him and if you're going to split you think that's enough punishment- going through the police process on top of everything else feels too much to bare.
BUT if o could give any advice from this side, report it, you don't have to support a police prosecution if you don't want to (just for clarity though some forces will arrest and push a victimless prosecution regardless, especially with injury evidence).
If he does get arrested the police can put bail conditions not to contact you should the case be take further or if it isn't, they can apply for a DVPN (if approved at court a DVPO) and again it will be conditions that he can't contact you for a certain amount of time, this will give you breathing space to process what's happened and what your next steps are going to be, move out if you want to etc.
It's also a record should there be issues over child access/custody, a referral would also be made to social services so again this is a protective measure for you and baby.
I don't know your history but if this is the first time, it won't be the last- it's not even low level, it's full punches in the face, if someone did this to you in the street they would deserve to get in trouble, let alone someone who is supposed to be your biggest protector.
Good luck OP, I hope you manage to stay strong and safe with whatever you decide to do