For many, personhood begins at conception. This view has been defended for centuries by various institutions, including the Roman Catholic Church, which considers all life sacred from conception until death. According to the Congregation for the Doctrine of the Faith, “Thus the fruit of human generation, from the first moment of its existence, that is to say from the moment the zygote has formed, demands the unconditional respect that is morally due to the human being in his bodily and spiritual totality. The human being is to be respected and treated as a person from the moment of conception; and therefore from that same moment his rights as a person must be recognized, among which in the first place is the inviolable right of every innocent human being to life” [7]. According to the major tradition of the Hindu faith, ensoulment of the fetus occurs at conception [8]. The fetus or embryo therefore has personhood and deserves protection. In Judaism, however, “according to the Talmud, within the first 40 days after conception the zygote is simply water” [9]. The fetus seemingly only attains full person status at birth. Yet, abortion “is not viewed as a morally neutral matter of individual desire or an acceptable form of post facto birth control” [9]. For Jehovah’s witnesses, life begins at conception, making abortion even if the life of the mother is in danger impermissible [10]. Finally, in Islam, ensoulment of the fetus is thought to occur between 40 and 120 days of gestation [11]. More recently, the concept of personhood beginning at conception has been supported by a wide range of philosophers. For scholars such as Larmer, “the potential for human consciousness is a sufficient condition of personhood and, since the fetus possesses this potential, is a person.” [3]. Many others also suggest that it is simply the potential to become conscious which obligates us to protect the life of a human organism [3].

This view of a fetus as a person has been largely influential in today’s political, ethical, and legal beliefs. It has shaped how abortion is viewed by many, how societies legislate in this matter, and how courts have set precedents. The notion of personhood at conception is also fundamental in the debate regarding the permissibility of in vitro fertilisation (IVF). It extends to how many embryos are created and used. During IVF, more than one embryo is frequently available to implant in the woman’s body. A physician can either implant all the generated embryos, which could be more than three or four, or implant one or two and freeze the remaining embryos. Implanting more than one embryo increases the chances of a successful pregnancy, but also increases the chances of twins and triplets or higher order multiple births. Multiple births increase the risks to pregnant women and their children, mainly because of the increased risk of prematurity. It has been demonstrated that implanting a maximum of one or two embryos is safer for women and future children. But in countries where there is a tradition of considering that a person exists from the time of conception, freezing remaining embryos is deemed either morally problematic or unacceptable. In these countries, this concept of personhood often determines regulations, banning freezing of embryos, even if implanting all of the harvested embryos represents significant health risks to both the mother and the fetuses. In some countries, during IVF, in cases of a multiple pregnancy with three or more embryos, selective abortions are often performed to “reduce” the pregnancy to a safer twin pregnancy. “Selective reductions” are not acceptable when personhood is defined as occurring at conception.

This definition of personhood has led many jurisdictions to limit or prohibit embryo and stem cell research, and to introduce restrictions on IVF. For example, in Germany, a law was enacted in 1992 prohibiting all research on human embryos that is not carried out exclusively to preserve embryos or facilitate uterine transfer [4]. In addition, only a maximum of three embryos can be transferred, none of them can be frozen after a certain stage, and all of the embryos produced have to be implanted. In Austria, as of 2008, preimplantation genetic diagnosis (PIGD) remains forbidden on the basis that embryos cannot be used for anything but pregnancy. In Italy, a religious Catholic country, only three eggs can be fertilized during IVF, even if more are generally produced after the burdensome process of ovulation induction. In addition, all embryos must be implanted. PIGD, genetic screening, and pregnancy reduction are not permitted. In Switzerland, PIGD is explicitly forbidden [4]. In Finland, PIGD diagnosis as well as the number of embryos transferred are not legally determined [4]. In Quebec (not in the whole of Canada), single embryo transfer is the norm. All remaining embryos are either destroyed, donated to science or to another couple, or frozen.

Variations also exist regarding the acceptability of embryonic research. In many countries where embryos can be frozen or donated, embryonic research—which can destroy the embryo—is permissible. It is performed on embryos that were not implanted during IVF. Regulations and ethical and scientific policies define a time during which embryonic research is acceptable, generally the first 14 days after fertilization [12]. In the USA, the Ethics Advisory Board (EAB) was appointed in 1978 with a mandate to review both IVF research and research using embryos resulting from IVF. The EAB did not support research on embryos older than 14 days but specified that embryos were different from persons: “The human embryo is entitled to profound respect; but this respect does not necessarily encompass the full legal and moral rights attributed to persons” [13]. Therefore, large variations exist in legislation, treatment of infertile couples, research, and care of pregnant women, affecting reproductive care and the outcome of children depending on the way personhood is defined.

A second answer to the question “When does the fetus become a person?” has been when the fetus begins to feel pain. As explained by Penner and his colleagues, “the claim is that the sensory input stored by the brain (along with other types of input later in life) is the essential basis upon which our experiential individuality as persons rests” [5], and “identifying the initiation of the coordinated functioning of these three aspects of the central nervous system of the fetus is the step that would convert this approach from a philosophical argument into a practical, pragmatic tool for promoting agreement among secularists regarding the time during gestation beyond which it is ethically impermissible to abort a fetus except under special circumstances.” [5]. The central nervous system appears during the third week post conception. The basic divisions of the brain start developing around a gestational age of six weeks. The first fetal movements have been detected at eight weeks of gestational age, but these are believed to be automatic, not voluntary, and are under the control of the brainstem [6]. This potential pain perception has influenced certain laws and regulations in relation to embryonic research.

However, pain is felt by all vertebrate animals. If pain is to define a person, then the cortical response to pain is what should be examined. Rudimentary cortical evoked responses to somatosensory stimulation can be recorded as early as 23–24 weeks of post-menstrual age (PMA), reflecting the beginning ingrowth of thalamocortical axons in the somatosensory cortex [6]. Functional thalamocortical connections are required for more advanced conscious perception of pain, and these appear around 29–30 weeks of gestation.

Already, these findings have had repercussions on the way current medicine is practiced. For example, analgesia is now given to fetuses before third trimester abortions in many centers. Most protocols include fentanyl administration before the feticide in order to make sure the fetus does not suffer from the termination of pregnancy. In the United States, legislation requiring physicians to inform pregnant women consulting for an abortion about fetal pain and fetal anesthesia is becoming more and more popular. States such as Nebraska, Idaho, Oklahoma, Kansas, Indiana, and Alabama have already passed laws to this effect [14].

Viability, too, has been a frequent answer to the question of when a fetus becomes a person. This argument has been crucial most notably in key legal cases such as Roe versus Wade in 1973, a famous American lawsuit. Jane Roe filed a suit to challenge the constitutionality of Texas abortion laws, which at that time made abortion a crime, except if it was performed to save the mother’s life. The U.S. Supreme Court chose to sidestep the issue of when the fetus becomes a person because of the sheer complexity of the religious, ethical, and philosophical implications. Instead, the majority of the Court decided to recognize the woman’s fundamental right to privacy and to control her own body, including making the decision to terminate a pregnancy. The majority of the Court acknowledged that although maternal health was important, protecting the potential of human life was also an important factor [15]. The state’s interest in fetal life becomes compelling when the fetus is declared viable, referring to the fetus’ ability to be “capable of a meaningful life outside the mother’s womb” [15]. After viability, the protection of the fetus becomes at least as important as the protection of the mother’s health. The Supreme Court’s decision has allowed the legal prohibition of third trimester abortions in many American states, except when medically necessary for the mother, and has greatly influenced all cases pertaining to unborn children, for example on statutes of wrongful death and homicide [15].