In practical usage, it is very similar to the English "bastard", seeing how the Spanish term "bastardo" is seldom if ever used as an insult by native speakers and means, very literally, an illegitimate child.
Call someone "miscarried" in English, or "bastardo" in Spanish, and they'll look at you funny. Call them a "malparido" or a "bastard" and they will take offense.
(Literal: That guy is miscarried through the a**)
(Paraphrased: That guy is one rat bastard)
english: that fuckin malparido is a bitch!