Determining the obligations owed to different parties in MFS requires first answering the question who or what exactly counts as a patient in this context. Two basic conceptualisations of the maternal–fetal relationship in the existing literature are the one-patient and two-patient model . On the former, the pregnant woman is considered to be the sole patient, with the fetus fully dependent on her for its survival and development.Footnote 4 Adopting this model would mean that we need only consider the pregnant woman’s decision about whether to engage in MFS. On the latter model, the fetus is recognised as a patient in its own right that can potentially have clinical interests distinct from those of the woman. The consequence of adopting this model could be a need to evaluate the interests of both patients when making decisions about MFS. Besides these basic two models, there are also some more sophisticated accounts that seek to overcome the tension between them, but that could be said to still fall somewhere in between these two camps.
One or Two Patients?
Some scholars, both in ethics and law, take the position that the fetus should be treated as part of the mother for the entire duration of the pregnancy up until birth, in which case there would be only one patient. This is also the approach adopted by many jurisdictions, such as the member countries of the European Union and the United States. In English law, some prominent court decisions have established that the fetus cannot be afforded legal personhood or any rights following from this: of particular significance are the cases of Paton v British Pregnancy Advisory Service, in which a husband unsuccessfully attempted to prevent the termination of his unborn child citing a right to life ; and Re F. (in utero), in which a local authority was denied their application to make the unborn child of a patient a ward of the court because the fetus has no status or rights of personhood in law allowing such an intervention .
The one-patient model has the distinct advantage of being consistent with how the law generally regards patienthood in MFS. Besides consistency with the law, there are also strong ethical arguments for treating the pregnant woman as the only patient. A significant worry about conceptualising the fetus as a patient is that this will lead to women being sidelined when debating the ethical implications of MFS, as the fetus might eventually come to be seen as the primary patient, or the more important of the two [34, 51]. Also, it seems conceptually and practically clear what we mean by saying that the pregnant woman is a patient in MFS. But it is less clear what it would mean for a fetus to be a patient, leading us to examine the two-patient conception of MFS.
It seems uncontroversial that pregnant women are patients in MFS, as their bodies are directly involved, and they are autonomous agents who are owed a duty of care. Fetuses certainly lack this key feature of autonomy. However, autonomy may not be necessary for patienthood, as we routinely speak of newborn babies or people in comas as patients, even though they are not autonomous. The fetus however, or more accurately the future child, stands to benefit directly from the surgical procedure, which cannot be said of the pregnant woman (except perhaps psychologically). When a newborn baby is treated for an illness, despite its complete lack of a developed sense of self, it seems plausible to speak of its clinical interests and the effects of treatment on its well-being. There is a significant (some would say crucial) difference in that the fetus exists within the woman’s body, so it depends on the mother for its life in the most literal sense. Still, if women are ready to permit interventions on their body in order to access the fetus and perform surgery on it, would clinicians be justified in treating that fetus as a kind of temporary patient ?
The two-patient view is often encountered in both public perceptions and the scientific literature, especially clinical [for some examples see 31, 46], but also ethical, as in this recent definition: “Surgical intervention on behalf of a fetus takes place, of course, inside a pregnant woman’s body, hence the reason it is sometimes called maternal–fetal surgery. (…) The ethical issues of fetal surgery are complicated since any intervention is invasive, often experimental, and involves two patients.” [24, my emphasis] This definition clearly shows in which sense the fetus might be seen not only as a patient, but as the primary patient, despite acknowledgment that it is confined to the woman’s body and that these interventions may pose risks to her health and well-being. Such framing fuels some of the worries about recognising fetal patienthood that will be discussed later in this paper.
Something like a middle ground between the one- and two-patient models can be found in accounts that take as a starting point the biological interdependence of the pregnant woman and fetus, and then propose a sense of patienthood that remains accepting of and appropriate to this basic fact. One such account is the ‘two-patient ecosystem model’ advocated by Susan Mattingly . This model of the maternal–fetal relationship stresses the biological unity and inseparability of the dyad. The fact that the fetus is incorporated in the pregnant woman in a very literal sense, on her account, will always trump any conceptual differentiation between the two. Mattingly suggests that it is precisely equivocation between the one- and two-patient accounts that leads to conceptual and practical confusion: “(…)treating the fetus as an independent patient but continuing to regard the pregnant woman as a compound patient incorporating fetus–has, I think, caused the physician's ethical dilemma to be misconstrued as a conflict between the duty to benefit the fetus and the duty to respect the woman's autonomy. (…) But fetal therapy is beneficial to the pregnant woman only on the old model, where she includes the fetus, while fetal harm is harm to another only on the new model, where the fetus is independent and exclusive of the woman.” [37, emphasis in original] According to her analysis, furthermore, recognising the fetus as a distinct patient actually strengthens the obligations doctors have towards pregnant patients: “Ironically, when the fetus is construed as a second independent patient, physicians' prerogatives to act as fetal advocates are actually diminished. This consequence flows not from any assumed superiority of maternal rights over fetal rights, but from differential professional duties to donors and recipients of medical benefits.”  Mattingly ultimately suggests that the way forward is not to deny the possibility of fetal patienthood, but instead “challenge the orthodox view of the professional-patient relationship, which suppresses dependency relations among patients and posits them as strangers to one another” , suggesting a family-oriented model of illness and treatment which focuses on relationships, protection, dependence and care.
This account seems highly plausible, not only in how it characterises the maternal–fetal relationship starting from the biological nature of the unit, but also in its demonstration that both the standard one-patient and two-patient models are respectively too simplistic to successfully address the ethical and practical reality of medical decision-making in pregnancy. However, its immediate normative implications, especially for the MFS context, are not entirely clear. The ultimate conclusion Mattingly reaches seems to be that maternal and fetal patients should be treated together almost as a compound patient: “when the various possible models of the maternal–fetal dyad are consistently applied, they converge to reinforce the physician's customary ethical stance—working cooperatively with the pregnant woman for common, linked goals of infant, maternal, and family well-being.”  This certainly should be, and seems to be, the usual goal of maternal–fetal specialists involved in MFS , but some would argue that wherever we have two patients, there is also the potential for conflict between their interests—and thus a way to resolve such conflicts is needed. I will now discuss an account which attempts to address precisely this problem, in various clinical contexts including MFS and prenatal therapy.
The Case for a Limited Sense of Fetal Patienthood: Chervenak and McCullough’s Ethical Framework
The standard two-patient model of the maternal–fetal unit in MFS posits that the fetus and the pregnant woman are two separate patients whose interests may conflict, leading to a situation where doctors may need to balance their obligations to each. This potential for separation can be addressed by stressing the unity of the maternal–fetal dyad, as Mattingly has done. Others, however, have suggested that a concept of fetal patienthood is necessary in order to resolve potential conflicts occurring, despite recognising that maternal and fetal interests are interwoven and independent . A notable account is the ‘fetus as a patient’ framework developed by obstetric ethicists Chervenak and McCullough. On this conception, a human being becomes a patient when 1) it is presented to the physician for medical care, and 2) there exist clinical interventions that are “are reliably expected to result in a greater balance of clinical benefits over harms for the human being in question”. [14,15,16]. Whether a fetus is a patient, then, does not depend on whether it possesses sentience, personhood, or some kind of intrinsic value; instead, this is determined in relation to the physician’s ability to provide treatment and, crucially, by the pregnant woman’s choice to present it for care. This assigns the fetus a kind of dependent moral status, distinct from the one possessed by the pregnant woman on the grounds of her personhood-relevant characteristics, and stemming wholly from its position as a patient, which is established when the criteria stated above are satisfied.
There are several advantages to this framework. As mentioned above, it aims to keep the thorny discussion about the moral status of the fetus outside of the MFS debate, as the fetus is assigned only dependent moral status as a patient. This assignment is meant to shift the focus from the moral status of the fetus to the obligations owed to the respective patients by medical professionals, which is highly significant for practical purposes, especially for resolving situations of maternal–fetal conflict. This framework also assigns a crucial role to the pregnant woman, in that it is only her autonomous decision that can confer patient status upon the fetus. Despite positing the existence of a fetal patient, then, this framework also shows due regard for women’s autonomy by specifying that it is the pregnant woman who enables patienthood, and therefore dependent moral status, to be conferred upon the fetus by choosing to present it for treatment – at least up to a certain point, as they accept that the moral situation may change after the viability threshold is passed [14, 15]. The doctor is seen to have only beneficence-based obligations to the fetal patient, while having both beneficence- and autonomy-based obligations to the pregnant woman, because of the aforementioned differences in their moral status.
Chervenak and McCullough’s framework however also faces some pressing problems. Firstly, it focuses mainly on the application of the four-principles framework to balancing the differing obligations to the maternal and fetal patient in cases of conflict. While a highly influential bioethical account in its own right, the four-principles theory of Beauchamp and Childress has also faced various kinds of criticism, leading some authors to argue that Chervenak and McCullough’s application of the framework here inherits some of these potential problems . Due to the prima facie nature of the principles involved (autonomy and beneficence), and lack of clarity on how these should be balanced in potential cases of conflict, these authors argue that the fetus as a patient account does not provide sound guidance for solving these problems in practice.
Secondly, significant objections are based on the possible threats to women’s autonomy and bodily integrity that may result from recognising the fetus as a patient. Chervenak and McCullough explicitly argue that, while the pregnant woman and the fetus are two patients, they are also inseparable and need to be considered together even if the respective obligations to each might differ. However, the worry here is that even acknowledging that the fetus and the pregnant woman might have separate, sometimes even conflicting interests, could justify treating them as separate, in the sense of acting in a way that will inevitably respect one set of interests but not the other [33, 34].
This ties into the final concern of whether their account truly manages to avoid granting independent moral status to the fetus. Rodrigues et al. point out that the conceptual connection between the fetus and the future child it will become actually smuggles in some kind of independent value for the fetus . Moreover, it is worth highlighting that the primacy of the pregnant woman – her ability to confer moral significance onto the fetus and waive it at any point – only applies before the viability threshold is reached, even though the fetus remains within her body after that. Therefore, it seems that, despite acknowledging the centrality of women’s autonomy in making decisions MFS and developing a notion of patienthood that avoids assigning a fetus independent moral status, Chervenak and McCullough’s theory ultimately inherits some of the most pervasive problems of the traditional two-patient model.
The two slightly modified accounts (the fetus as a patient and the ecosystem model) present improvements in that they look at the actual, lived nature of the maternal–fetal relationship as a basis for their ethical position, and also in that they probe more deeply into the concept of patienthood instead of assuming that is has a clear meaning. Still, both of these views entail some recognition of fetal patienthood, therefore making it necessary to examine whether there are other inherent dangers to accepting the existence of fetal patients in any sense.