Shanna Moakler Announces Pregnancy Week After BF's Arrest

Shanna Moakler's traumatic week is taking a huge turn -- she just announced she's pregnant with her 4th child, days after her boyfriend Matthew Rondeau was arrested for allegedly hitting her.

Shanna says she took a pregnancy test that came up positive, and it's clear she's shocked by the news. In a statement, she said, "This has been a very difficult week, but I'm taking everything day by day."

As we reported, Rondeau was arrested for felony domestic violence last week.

Law enforcement sources tell TMZ Shanna and Matthew got in a heated argument last Wednesday night ... Shanna left home but returned Thursday morning where the arguing continued and allegedly got physical.

We're told cops were called, and Shanna had visible marks on her body ... prompting officers to arrest and book Rondeau for felony domestic violence.

Rondeau posted an aggressive video on her social media before his arrest, claiming Shanna cheated on him and swearing he'd never get back with her.