Is It a Miscarriage or a Premature Delivery?

Exodus 21, 22 through 23 deals with the punishment for causing miscarriage. The one who hurt her shall be fined according as the woman's husband shall lay upon him and he shall pay as the judge is determined. If any harm follows, then you shall give life for life. Some people have read the text to say that it's dealing with not miscarriage, but a premature delivery.