In antiquity, the fetus was sometimes protected by restrictions on abortion. Some versions of the Hippocratic Oath indirectly protected fetus by prohibiting abortifacients. Until approximately the mid-19th century, philosophical views on the fetus were influenced in part by Aristotelian concept of delayed hominization. According to it, human fetuses only gradually acquire their souls, and in the early stages of pregnancy the fetus is not fully human. Relying on examinations of miscarried fetuses, Aristotle believed that male fetuses acquire their basic form at around day 40, and female ones at day 90. For Pythagoreans, however, fetal life was co-equal in moral worth with adult human life from the moment of conception; similar views were held by Stoics. Ancient Athenian law did not recognise fetal right to life before the ritual acknowledgement of the child. The law, however, allowed to postpone the execution of sentenced pregnant women until a baby was delivered.
Several Hindu texts on ethics and righteousness, such as Dharmaśāstra, give fetus a right to life from conception, although in practice such texts are not always followed.
The property law of the Roman Empire granted fetus inheritance rights. As long as the fetus was conceived before the testator's death (usually, the father) and then born alive, his or her inheritance rights were equal to those born before the testator's death. Even though under the Roman law the fetus was not a legal subject, it was a potential person whose property rights were protected after birth. Roman jurist Ulpian noted, that "in the Law of the Twelve Tables he who was in the womb is admitted to the legitimate succession, if he has been born". Another jurist Julius Paulus Prudentissimus similarly noted, that "the ancients provided for the free unborn child in such a way that they preserved for it all legal rights intact until the time of birth". The inheritance rights of the fetus were means of fulfilling the testator's will. The interests of the fetus could be protected by a custodian, usually a male relative, but in some cases a woman herself could be appointed the custodian. The Digest granted the fetus consanguinity rights, vesting the protection of fetal interests in the praetor. The Digest also prohibited the execution of pregnant women until delivery. The Roman law also envisaged that if a slave mother had been free for any period between the time of the conception and childbirth, the child would be regarded as born free. Although the mother might have become slave again before the childbirth, it was considered that the unborn should not be prejudiced by the mother's misfortune. At the same time, Greek and Roman sources do not mention issues of alcohol consumption by pregnant women. On that basis it is believed that Greeks and Romans were not aware of the fetal alcohol syndrome.
A baby holding the "Petition of the Unborn Babes", 18th century illustration.
After the spread of Christianity an issue emerged on whether it was permissible for a pregnant woman to be baptised before childbirth, due to uncertainty as to whether the fetus would be cobaptised with its mother. The Synod of Neo-Caesarea decided that the baptism of a pregnant woman in any stage of gestation did not include the fetus. In the Middle Ages, fetal rights were closely associated with the concept of ensoulment. In some cases the fetus could also inherit or be in the order of succession. In the Byzantine Empire, fetus was regarded as a natural person and could inherit alongside blood descendants and slaves. Byzantine Emperor Michael VIII Palaiologos allowed soldiers to transfer their pronoiai to their unborn children. The unborn royals were increasingly granted the right to succession. In 1284, King of Scotland Alexander III designated his future unborn children as heirs presumptive by the act of parliament to avoid potential squabbles among loyal descendants of his lineage. The 1315 entail of Scottish king Robert the Bruce allowed the unborn collateral individuals to be in line for the throne beyond his brother Edward and daughter Marjorie Bruce. After the death of Albert II of Germany in 1439, his then-unborn son Ladislaus the Posthumous inherited his father's sovereign rights. In 1536, the British Parliament gave the unborn children of Henry VIII and Jane Seymour precedence in the line of royal succession. The medieval distinction between the ensouled and the unensouled fetus was removed after Pope Pius IX decreed in 1854 that the ensoulment of Virgin Mary occurred at conception.
In 1751, a pamphlet "The Petition of the Unborn Babes to the Censors of the Royal College of Physicians of London" by physician Frank Nicholls was published, advocating fetal right to life and protection. The pamphlet anticipated many of the arguments of the 21st century's pro-life movement. In 1762, English jurist and judge William Blackstone wrote that an "infant in its mother's womb" could benefit from a legacy and receive an estate as if it were actually bom. The fetus was thus considered a person for purposes of inheritance. Similarly to the Roman law, the Napoleonic Code envisaged that if a woman becomes a widow, a male guardian should be appointed for her unborn child.
In the 20th century and particularly after World War II fetal rights issues continued to develop. In 1948, the Declaration of Geneva was adopted which prior to amendments in 1983 and 2005, advised physicians to "maintain the utmost respect for human life from the time of its conception". In 1967, American Bar Association Journal noted "the modern trend of legal decisions that grant every property and personal right to the unborn child, including the right to life itself, from conception on". In 1975, while interpreting the right to life under the Basic Law of Germany, the Federal Constitutional Court opined that "life in the sense of historical existence of a human individual" exists "at least from the 14th day after conception (nidation, individuation)" and thus everyone's right to life under the Basic Law of Germany includes the unborn as human beings. The 1980s witnessed the reappearance of fetal protection in the workplace, aimed at guarding fetal health in potentially hazardous working conditions. In 1983, Ireland was one of the first countries in the world to constitutionalize a fetal right to life by passing the Eighth Amendment to the Constitution, later repealed in September 2018.