Today, we'll focus on the background, and abortion in the USA prior to Roe v. Wade in 1973. For the first few decades of its history, there were no laws on the books outlawing abortion: it was subject to English common law.
Under English common law, abortion prior to "quickening" - where the foetus's movements are first felt, which is usually between 15-20 weeks of pregnancy - was not an offence. It was not permitted after this point.