In antiquity, a 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 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.
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 descendents 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 became the first country in the world to constitutionalize fetal right to life by passing the Eighth Amendment to the Constitution.
The only modern international treaty specifically tackling the fetal rights is the American Convention on Human Rights which envisages the fetal right to life from the moment of conception. The convention was ratified by twenty five countries of the Americas in 1973–1993. Mexico ratified the convention with the reservation that the expression "in general" concerning the fetal right to life does not constitute an obligation and that this matter falls within the domain of the states. While the convention may theoretically permit domestic abortion laws in exceptional circumstances, it effectively declares the fetus a person.
Based on the 1959 Declaration of the Rights of the Child, preambular paragraph 9 of the Convention on the Rights of the Child (CRC) states that "the child... needs... appropriate legal protection before as well as after birth", but due to ambiguity the legal protection of the fetus conflicts with the rights of a pregnant girl under the same Convention. Such conflict is sometimes called maternal–fetal conflict. Under CRC, the rights of a pregnant girl are interpreted as superseding those of her fetus. The states retain the power to decide for themselves what prenatal legal protection they would adopt under CRC. A proposal to grant fetus the right to life from conception was put forward by Belgium, Brazil, El Salvador, Mexico and Morocco during drafting of the International Covenant on Civil and Political Rights (ICCPR), but it was rejected in favor of less stringent wording. At the same time, ICCPR prohibits the execution of pregnant women.
The World Medical Association Declaration on Therapeutic Abortion notes that "circumstances bringing the interests of a mother into conflict with the interests of her unborn child create a dilemma and raise the question as to whether or not the pregnancy should be deliberately terminated". The Dublin Declaration on Maternal Health, signed in 2012, prioritizes fetal right to life by noting that "there is a fundamental difference between abortion, and necessary medical treatments that are carried out to save the life of the mother, even if such treatment results in the loss of life of her unborn child". Several organizations, such as World Health Organization (WHO) and Human Rights Watch prioritize women's reproductive rights over fetal rights.
Under European law, fetus is generally regarded as an in utero part of the mother and thus its rights are held by the mother. The European Court of Human Rights opined that the right to life does not extend to fetuses under Article 2 of the European Convention on Human Rights (ECHR), although it does not confer on the European Court of Human Rights the authority to impose relevant laws on European Union member states. In H. v. Norway, the European Commission did not exclude that "in certain circumstances" the fetus may enjoy "a certain protection under Article 2, first sentence". Three European Union member states (Ireland, Hungary and Slovakia) grant fetus the constitutional right to life. The Constitution of Norway grants the unborn royal children the right of succession to the throne. In English common law, fetus is granted inheritance rights under the born alive rule.
Islamic law grants the fetus the right to life particularly after ensoulment, which according to various Islamic jurists happens after 40–42 days or four months after conception (some Shiite jurists believe the ensoulment occurs after 11 to 14 days, during the implantation of the fertilized egg in the uterine wall). Both the Sunni and Shiite jurists accord the fetus inheritance rights under two conditions: if a man dies and a pregnant wife survives him, the fetal right to inherit is secure and the inheritance cannot be disposed of before the fetus' share is set aside. Under the second condition, if a woman aborts the fetus at any stage and ignores any vital signs, the fetus is entitled to the inheritance of any legitimate legator who dies after its conception.
The legal debate on fetal rights sometimes invokes the notion of fetal viability. Its primary determinant is fetal lung capacity which typically develops at twenty-three to twenty-four weeks. The twenty-three weeks is usually regarded as the lower bound of fetal viability because technology has been unable to surpass the limit set by lung development. It was nonetheless stated that technology has made it possible to regard the fetus as a patient independent of the mother. In Winnipeg Child and Family Services v. G., the judges argued that "technologies like real-time ultrasound, foetal heart monitors and foetoscopy can clearly show us that the foetus is alive" and thus the born alive rule is "outdated and indefensible".
The creation of human embryos for all research purposes is prohibited by the Convention for the Protection of Human Rights and Dignity of the Human Being with regard to the Application of Biology and Medicine. However, similarly to the abortion debate, in the normative debate on embryo research two views can be distinguished: a "fetalist" view focusing on the moral value of the embryo, and a "feminist" view advocating the interests of women, particularly candidate oocyte donors.
Fetal right to life is envisaged in the Constitution of Chile, Dominican Republic, Ecuador, El Salvador, Guatemala, Hungary, Ireland, Philippines and Slovakia. The Constitution of Honduras grants the unborn all rights accorded by country's law. The Constitution of Peru similarly declares fetus "a rights-bearing subject in all cases that benefit him". The Constitution of Madagascar grants the unborn the right to the health protection through free public health care.
In the United States, as of 2014, thirty-eight states provide certain level of criminal protection for the unborn, and twenty-three of these states have laws that protect the fetus from conception until birth. All US states–by statute, court rule or case law–permit a guardian ad litem to represent the interests of the unborn. In 1999, the Unborn Victims of Violence Act was introduced into United States Congress which defines violent assault committed against pregnant women as being a crime against two victims: the woman and the fetus she carries. This law was passed in 2004 after the murder of Laci Peterson and the fetus she was carrying. In 2002, U.S. President George W. Bush announced a plan to ensure health care coverage for fetuses under the State Children's Health Insurance Program (SCHIP).
The civil codes of several countries, such as China (including Hong Kong and Macau) and Russia, as well as some US states, grant fetus inheritance rights, usually under the born alive rule. In the civil code of Iran, fetus can inherit in case of abortion that took place due to a crime, as long as the fetus was alive even for a second after birth. Under the civil code of Japan, for the purposes of inheritance the fetus is deemed to have already been born. The civil codes of the Philippines and Spain envisage that donations to the unborn children can be made and accepted by "persons who would legally represent them if they were already born". The same is allowed by the Malikis.
Alongside Norway, the Constitution of Bhutan grants the unborn royal children the right to succession, but only if there is no male heir.
Various initiatives, prompted by concern for the ill effects which might be posed to the health or development of a fetus, seek to restrict or discourage women from engaging in certain behaviors while pregnant. Also, in some countries, laws have been passed to restrict the practice of abortion based upon the gender of the fetus.Many jurisdictions actively warn against the consumption of alcoholic beverages by pregnant women, recommending a maximum intake or total abstinence, due to its association with Fetal alcohol syndrome. Countries that encourage those who are pregnant to avoid alcohol either entirely or partially include Australia, Canada, France, Iceland, Israel, the Netherlands, Norway, New Zealand, Spain, the United Kingdom, and the United States.
Many national and international agencies recommend dietary guidelines for pregnant women due to the health risks posed by the consumption of fish contaminated with methylmercury through industrial pollution. Studies have linked exposure to various levels of methylmercury in utero to neurological disorders in children.
The use of tobacco products or exposure to secondhand smoke during pregnancy has been linked to low birth weight. Governor Mike Huckabee of Arkansas, citing studies which attribute 10% of infant deaths to tobacco-smoking mothers, considered adopting a smoking ban for pregnant women in 2006 with the aim of reducing infant mortality.
No U.S. state has enacted a law which criminalizes specific behavior during pregnancy, but, nonetheless, it has been estimated that at least 200 American women have been criminally prosecuted or arrested under existing child abuse statutes for allegedly bringing about harm in-utero through their conduct during pregnancy. Reasons for pressing charges included use of illicit drugs, consumption of alcohol, and failure to comply with a doctor's order of bedrest or caesarean section. Drug addicts have been accused of "supplying drugs to a minor" through unintentional chemical subjection via the umbilical cord. Others have been charged with assault with a deadly weapon with the "deadly weapon" in question being an illegal drug. Minnesota, Wisconsin and South Dakota allow women who continue to use substances while pregnant to be civilly committed. Some states require that medical providers report any infant who is born with a physical dependency, or who tests positive for residual traces of alcohol or drugs, to child welfare authorities.
Cultural preferences for male children in some parts of Asia, such as Mainland China, India, South Korea, and Taiwan, have sometimes led to sex-selective abortion of female fetuses, leading to the disparity between male-to-female birth rates which is observed in some places. India banned the practice of abortion for reasons of fetal sex in 1994.