It was understood by ancient commentators (i.e., in the Talmud) to refer to miscarriage. This would mirror other laws in the ancient near east that imposed a fine for inducing miscarriages and death for murdering an adult, like the Code of Hammurabi (law 209).
It seems like you're taking one literal interpretation of a specific English translation as the only legitimate reading. There is plenty of scholarship and commentary by ancient and contemporary authors who can shed light on how the text was read (and, in this case, upheld in a legal setting) in the original Hebrew.
It seems like you're taking one literal interpretation of a specific English translation as the only legitimate reading. There is plenty of scholarship and commentary by ancient and contemporary authors who can shed light on how the text was read (and, in this case, upheld in a legal setting) in the original Hebrew.