A great post by David Mathis at Desiring God: The Baby in My Womb Leaped for Joy:
Luke uses the word "baby" to denote not only the post-born Jesus in the manger (2:16) but also the preborn John in the womb (Luke 1:41, 44). Luke also notes that the preborn John was "filled with the Holy Spirit," a reality which the Bible only ascribes to persons.
The assumption is that the baby in the womb is a person. And the implication is that human life in the womb should be protected.