I would guess that since at least the time of
Hippocrates since the
Oath he authored prohibits abortion. In both versions, it is specifically connected to “deadly things.”
Hippocrates predates the Church by hundreds of years.
To be fair, Hippocrates’ understanding of ‘abortion’ isn’t quite the modern understanding. In fact, he described performing a form of late term, partial birth abortion for the sake of a seriously deformed child (a mercy because of the child’s prospects in life).
Tertullian one of the first great Latin Christian apologists, in his treatise on the human soul also describes a similar procedure, in fairly gruesome detail, and declares that it is morally just, even though his general take on abortion is very close to our modern understanding (though his theological argument for it is different and would now be considered heretical).
The first century Didache condemns abortion as murder:
From a scholarly point of view, it’s not quite clear what precisely the Didache means. Remember, it was a work of Jewish-Christians. The Hilacha held that the reason that personhood is at birth is that ensoulment was a mystery that would be revealed after the Messiah.
The break with Judaism from birth to quickening appears to date from this time (prophecy fulfilled?). It is not clear if the Didache, or many of the earliest writings mean all abortions or post ensoulment abortions because the quickening standard emerged from oral tradition from the same period.
I know it is popular to cite early writings on abortion, but we have to be careful. Two of the most popular quotes are from Tertullian, but right smack in the middle of them in the original text is a gruesome partial birth abortion, argued as just (see above), though we would argue it as not just today.
What we can say with some certainty is that our roots come from the most pro-life tradition in that quadrant of the world at that time. At the time of Christ, Jews already viewed abortion as an attack on the potential person and very limited in permissibility. Christians went farther and argued that personhood was at quickening (something we do not hold dogmatically to be certain, but it is the longest tradition), but that was a theological distinction, it doesn’t automatically mean that Christians were even more stringent on abortion than Jewish tradition.
Chances are good it wasn’t. Pauline Christianity thrived in the gentiles, and we had a lot farther to mature morally. For the first 1000 years of the Church the big battle wasn’t educating us about abortion, it was breaking us from our traditions of infanticide.