People used to think of and experience pregnancy very differently than we do today.
Prior to the late 19th Century, most people (in the United States, anyway) did not consider a pregnancy a “true” pregnancy until what was known as the ‘the quickening’ – the moment when the fetus had developed enough to begin moving in utero, and the point at which the mother becomes aware of the fetus’ movement. This usually happened somewhere between the 2nd and the 5th month of pregnancy (it varies a lot, depending in large part on how many children the mother has had).
It was only after the quickening that a woman would be “officially” and legally pregnant – prior to that, the only symptom of pregnancy (apart from hormonal symptoms) was the absence of menses. In a time period when “instant” pregnancy tests (which test for HCG hormone) did not exist, and when there were many other reasons why women might not menstruate (ie, malnutrition, illness, etc), people could never be certain that a missed or late period necessarily meant pregnancy. As a result, early miscarriages (before the quickening) weren’t usually looked upon as the loss of a fetus – rather, this was simply referred to as the “restoration of menses,” and people did not look upon this as the loss of a (potential) child. Most churches did not consider a fetus to have a soul until after the quickening, and the law did not recognize the existence of a fetus until after the quickening had occurred – as a result, abortions or procedures to “restore the menses” that occurred prior to the quickening were perfectly legal. A famous case in Massachusetts (Commonwealth v Bangs) made this clear in 1812, and for much of the remainder of the 19th Century abortion before the quickening was both common and acceptable – many “home manuals” aimed at women even contained instructions on how to do it using abortifacients.
This began to change in the late 19th Century, with the rise of a powerful movement against abortion and abortionists led by medical doctors, and the American Medical Association. The primary motive for this drive, though, was one of professionalization; doctors were opposed to abortions not because they were morally or theologically opposed to the idea of abortions, but rather because they felt that abortionists (usually midwives and folk healers) were honing in on their professional turf, and weren’t sufficiently knowledgable or professional enough to perform these procedures. One of the main effects of their attempts to drive abortionists out of business, however, was that abortion itself (both early-term and late-term) became increasingly illegal, ironically driving women to even-more-shady back-alley type abortionists, rather than to the quasi-professional practitioners who they had had access to before.
James Mohr, Abortion in America: The Origins and Evolution of National Policy
Shoshana Ehrlich, Who Decides