It is traditionally translated as miscarry in the Jewish texts.
However the literal translation is just that the child exits the woman and no specific mechanism of exiting is mentioned.
I am going to go out on a limb here and guess that the different translations are based on the phrase "and there was no fatality/disaster/accident." The question is, who's fatality are we concerned about? The child's or the woman's? Based on the context of the verse, and I believe the grammatical formation of the words, it is clear that the "woman" did not die, and not that the baby did not die.
I can foresee many arguments given for why it is obviously the woman, and only 1 argument that it is talking about the baby. The argument which suggests it is talking about the baby however is an argument based on imposed ignorance. I.e., even if with all other information we know about Jewish law, it must be talking about the woman, maybe in this one case it's not.
IMO if you want to argue that the verse is talking about a pre-mature birth, you are going to need REALLY strong argument that "and there was no fatality/disaster/accident" is talking about the unborn child.