Please consider that your friend maybe be in an abusive relationship.
It’s proven that domestic abuse rises significantly after pregnancy and birth.
Do some research for yourself, assess it and act accordingly.
You say the partner has turned other friends away and you’re all a big supportive group from uni days that go on girly holidays. If this is domestic abuse, you won’t be “acceptable friends”. Breaking a support network is a key part of an abusive relationship.
You say the partner is new, you can phone the police and ask for Claire’s Law. They will disclose any intelligence if it’s relevant and signpost to agencies to help your friend if needed.
Consider that the friend maybe hesitant to disclose anything out of fear and may defend their relationship. Perhaps ask something like “have you ever wanted to tell me anything but felt like you couldn’t” - this will usually open a conversation for a victim. Listen and validate.
If you go round to the house consider ring doorbells and drop in Alexa’s that might be monitoring her contact.
Just like safeguarding children is everyone’s job, safeguarding any adult (vulnerable or not) against domestic abuse is a role for everyone.
Please don’t “let them get on with it” as some have suggested. You can do that once you know your friend and the baby are safe and not suffering in an abusive environment.
If it’s happening you could potentially save your friend and baby from years of emotional/physical trauma or even worse death. You won’t regret acting on it.
At the moment you’ve got nothing to lose!