"Sweet pregnancy" is an exclamation of surprise used in American English. The phrase was coined in 2006 in an office at WVU. It was derived from phrases such as, "Holy shit!" or "Sweet Jesus!", yet it is superior to those considering how pregnancy comes as an unwelcome surprise for many college-age females.
Logan: "There are only 3 cans of Beer 30 left!"
Ben: "Sweet pregnancy! We better get some more."