According to Joseph Dellapenna in his Dispelling Myths of Abortion History, that assertion is incorrect.
Before the 19th century, Common Law did not have any statutes prohibiting such widely recognized crimes such as rape and murder. The Law was not written down so much as handed on through common understanding and precedent. The 19th century was the age of legal codification. All of the world’s developed countries developed country passed laws against abortion, including England and America.
It’s not that the absence of such statutes signaled the legality of abortion. It’s just that, as with other serious crimes, their prohibition was assumed through common legal precedent. It was assumed that abortion took the life of a human being, whether the child was quickened or not.
The question at the time was whether abortion consisted of a felony or a misdemeanor (or in 19th century language “misprision”). Due to a misreading by Sir Edward Coke, one of the most prominent voices in Common Law history, whose precedent was cited even if he was obviously wrong (as Dellapenna thinks he was in this situation), abortions were considered misdemeanors before quickening.
It’s not that abortion was not considered a serious crime before quickening. It had to do with the nature of the prosecution itself.
“At the time, to prove that an abortional act caused the death of a child, one would have to prove both that the child was alive when the act was committed and that the act rather than some supervening act or event caused the abortion. Given the primitive state of gestational and forensic knowledge, both proofs could often be problematic. The problem is hardly surprising. Forensic medicine remained extremely primitive even three centuries later. In 1601, no certain means of proving that a woman was even pregnant existed until the infant had ‘quickened,’ that is had begun to move so that the mother (and others) could feel this movement. A relatively certain clinical test for pregnancy did not emerge until 1927. Thus even the fact of pregnancy was virtually impossible to prove, unless the mother had aborted and she (or someone else) preserved the remains of the abortus or if the mother died and an autopsy were performed. Even experienced mothers were often uncertain [and I can attest to this!]. “
Since pregnancy before quickening was hard to establish, they were rarely if ever prosecuted. The lack of prosecution is one piece of evidence adduced to point to the supposed legality of abortion. But that wasn’t the case at all. It wasn’t that abortions were legal; it was that they were difficult to prosecute. And, being as they were so difficult to prosecute, it was feared that juries would not convict if the crime of abortion before quickening were considered a felony, seeing as the evidence could be uncertain. Thus it as considered a misdemeanor.
The other proof that Dellapenna shows that abortion was not a liberty before the 19th century is that until 1968, when law professor Cyril Means Jr. wrote of this liberty, no legal document had ever spoken of it. “The unanimous sense of the legal and the general community was that abortion was a crime because it involved the killing of a child—if one could prove that the child was alive at the time of the abortive act and died as a result.”