Was this law only applied in the case of the pregnant woman?

No, in Leviticus, God generalizes this law: “If anyone injures their neighbor, whatever they have done must be done to them: fracture for fracture, eye for eye, tooth for tooth. The one who has inflicted the injury must suffer the same injury.” This teaches that what one sows, one also reaps, and that evil brings harm to the wrongdoer. The judgments in such cases were usually carried out by the judges, as we also read in Deuteronomy.