The upcoming Old Testament lection comes from Jeremiah 1:4-10. In my study, I found the comments of Tertullian of Carthage (late 2nd/early 3rd centuries) on verse five to be very interesting in relationship to the issue of abortion.
Jeremiah 1:5 quotes God as saying: "Before I formed you in the womb I knew you, and before you were born I consecrated you; I appointed you a prophet to the nations" (NRSV).
Tertullian comments: "The embryo therefore becomes a human being in the womb from the moment that its form is completed. The law of Moses, indeed, punishes with due penalties the one who shall cause an abortion, inasmuch as there exists already the rudiment of human being that has imputed to it even now the condition of life and death, since it is already liable to the issues of both, although, by living still in the mother, it for the most part shares its own state with the mother" (One the Soul 37. As found in Ancient Christian Commentary on Scripture, OT XII).
One might ask what Tertullian means by "the moment that its form is completed" (emphasis, mine). One could argue from the remainder of his comments that one need not think in literal terms of absolute completion of form; that, instead, it could be argued that Tertullian would accept the "completion" of conception, i.e., once a human being has been formed in terms of conception. However one may answer that question, it is clear that his comments refer to one (in this case, Jeremiah) who is not yet born.
What I find of interest in this passage, along with the story of the blessed virgin Mary's visit to Elizabeth, is how God is actively at work in and through those (i.e., Jeremiah, John & Jesus), who had not yet been born.
In Jeremiah's case, God knew him even before he was formed in the womb, and before he was born, God consecrated/sanctified him and appointed him to be a prophet.
In John's case, he is filled with the Holy Spirit before he is born (cf., Luke 1:15), and he actually prophesies prior to his birth (by virtue of his "leap[ing] for joy," and through the words of his mother), as one sees in Luke 1:41-45.
In addition to whatever weight these passages might add to the argument that infants are proper candidates for baptism, they certainly support those churches (like the Church of the Nazarene) that take a stand for life.