Deputies responded to a report of domestic violence in an unincorporated area of Monterey County near Salinas at about 10:30 a.m., and found the victim, who is three months pregnant, with bruises on her face and body.
Sheriff's investigators believe the wounds were inflicted by the victim's boyfriend, Larry Wade Seta.
The victim had discovered text messages from another person on Seta's cell phone, and sheriff's investigators said the ensuing argument turned violent when Seta, who had been drinking, allegedly struck the victim on her belly with his knee.
Seta then allegedly threw her to the ground, punching and stomping on her body and head before striking her with a curtain rod, according to the sheriff's office.
The victim fled to a neighbor's home and later reported the incident.
A family member transported her to a hospital, where she was treated for her injuries.
Deputies located and detained Seta, who they determined was also in violation of parole, at 12801 Rogge Road in Salinas.
Seta was arrested and booked into Monterey County Jail on charges of domestic violence, assault and violation of parole, a sheriff's deputy said.