26-year-old Aaron McKenzie stabbed Kelly Fauvrelle 21 times in the middle of the night. Her baby boy Riley, who was delivered by Caesarean, died four days later.
He was sentenced to life with a minimum 35 years for the murder Ms Fauvrelle at the Old Bailey on Friday.
He also received 20 years for the manslaughter of baby Riley and three years for possession of a knife.