The artificial uterus: on the way to ectogenesis

Abstract

The inability to support the growth and development of a mature fetus up to delivery results in significant human suffering. Current available solutions include adoption, surrogacy, and uterus transplantation. However, these options are subject to several ethical, religious, economic, social, and medical concerns. Ectogenesis is the process in which an embryo develops in an artificial uterus from implantation through to the delivery of a live infant. This current narrative review summarizes the state of recent research focused on human ectogenesis. First, a literature search was performed to identify published reports of previous experiments and devices used for embryo implantation in an extracorporeally perfused human uterus. Furthermore, studies fitting that aim were selected and critically evaluated. Results were synthesized, interpreted, and used to design a prospective strategy for future research. Therefore, this study suggests that full ectogenesis might be obtained using a computer-controlled system with extracorporeal blood perfusion provided by a digitally controlled heart-lung-kidney system. From a clinical perspective, patients who will derive significant benefits from this technology are mainly those women diagnosed with anatomical abnormalities of the uterus and those who have undergone previous hysterectomies, numerous abortions, and experienced premature birth. Ectogenesis is the complete development of an embryo in an artificial uterus. It represents the solutions for millions of women suffering from premature deliveries, and the inability to supply growth and development of embryos/fetuses in the womb. In the future, ectogenesis might replace uterine transplantation and surrogacy.

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Zygote
cambridge.org/zyg
Research Article
Cite this article: Bulletti FM et al. (2023). The
artificial uterus: on the way to ectogenesis.
Zygote. page 1 of 11. doi: 10.1017/
S0967199423000175
Received: 27 July 2022
Revised: 25 February 2023
Accepted: 23 March 2023
Keywords:
artificial uterus; ectogenesis; ectogestation;
recurrent preterm birth; uterine anatomical
abnormalities
Corresponding author: Carlo Bulletti;
Email: carlobulletti@gmail.com
© The Author(s), 2023. Published by Cambridge
University Press.
The artificial uterus: on the way to ectogenesis
Francesco Maria Bulletti1, Romualdo Sciorio2, Antonio Palagiano3and
Carlo Bulletti4
1Department Obstetrics and Gynecology Lausanne, Switzerland; 2Edinburgh Assisted Conception Programme,
Royal Infirmary of Edinburgh, Edinburgh EH16 4SA, UK; 3Reproductive Science Pioneer, Assisted Fertilization
Center (CFA), Naples, Italy and 4Extra Omnes, Assisted Reproductive Technology (ART), Center in Cattolica, Italy,
and Associate Adjunct Professor, Department of Obstetrics, Gynecology, and Reproductive Science, Yale
University, New Haven, Connecticut, USA
Summary
The inability to support the growth and development of a mature fetus up to delivery results in
significant human suffering. Current available solutions include adoption, surrogacy, and ute-
rus transplantation. However, these options are subject to several ethical, religious, economic,
social, and medical concerns. Ectogenesis is the process in which an embryo develops in an
artificial uterus from implantation through to the delivery of a live infant. This current narrative
review summarizes the state of recent research focused on human ectogenesis. First, a literature
search was performed to identify published reports of previous experiments and devices used
for embryo implantation in an extracorporeally perfused human uterus. Furthermore, studies
fitting that aim were selected and critically evaluated. Results were synthesized, interpreted, and
used to design a prospective strategy for future research. Therefore, this study suggests that full
ectogenesis might be obtained using a computer-controlled system with extracorporeal blood
perfusion provided by a digitally controlled heart–lung–kidney system. From a clinical perspec-
tive, patients who will derive significant benefits from this technology are mainly those women
diagnosed with anatomical abnormalities of the uterus and those who have undergone previous
hysterectomies, numerous abortions, and experienced premature birth. Ectogenesis is the com-
plete development of an embryo in an artificial uterus. It represents the solutions for millions of
women suffering from premature deliveries, and the inability to supply growth and develop-
ment of embryos/fetuses in the womb. In the future, ectogenesis might replace uterine trans-
plantation and surrogacy.
Introduction
Medically assisted reproduction (MAR) has undergone a marked evolution over the past dec-
ades. Initially, in the seventies it was only considered an experimental procedure. Currently,
MAR plays a major role in mainstream medicine and has facilitated the conception and delivery
of more than nine million babies (Steptoe and Edwards, 1978; Bulletti et al.,1986,1987,1988a,
1988b; Palermo et al.,1992; Thoma et al.,2013; Suzuki, 2014; Brännström et al.,2015; De Geyter
et al.,2020; Roseboom and Eriksson, 2021). However, there are still many unresolved concerns
associated with uterine anomalies, as well as other aspects of reproductive dysfunction. Critical
aspects correlated with preterm delivery (World Health Organization, 2017), premature uterine
removal, and discrepancies between a given genetic state and the psychological desire for pro-
creation are among the most common causes of infertility. Similarly, ethical, religious, social,
and economic conditions, as well as the region-specific legal status of MAR technologies, con-
tribute to the increased pain experienced by couples who remain unable to conceive. Ectogenesis
has been presented as a potential solution for many of these concerns, allowing women who are
currently incapable of supporting full gestation to have children and become biological parents.
Therefore, the purpose of this narrative review is to present an overview of recent developments
in ectogenesis and to explain how this practice might circumvent problems associated with ute-
rine dysfunction. The study will also examine the main ethical considerations associated with
ectogenesis and how they might be resolved. The goals of this study include:
•Identification of methods that might be used to prolong human embryo culture.
•Exploration of the possibility of preserving and monitoring premature fetuses (<24 weeks)
with a survival system that involves a fluid-to-fluid computer-controlled connection that
promotes their development and maturation.
•Evaluation of the pros and cons of supporting an excised donor-provided uterus to support
a complete pregnancy up to delivery by the use of external vascular connections rather
than internal transplantation.
•Development of a physical system that can be used to support full ectogenesis.
https://doi.org/10.1017/S0967199423000175 Published online by Cambridge University Press

Materials and methods
The main aim of the current review was to focus on the question of
whether it will be possible shortly to perform human ectogenesis.
To achieve this goal, a literature search was performed analyzing
the PubMed and Google Scholar beta databases, aiming to identify
the animal and human studies of experiments and devices applied
in the ectogenesis procedure. Inclusion criteria were experimental
studies published in English on in vitro embryos culture, implan-
tation, differentiation and development, artificial uterus, ectogen-
esis, ectogestation, preterm birth, uterine abnormalities, liquid-to-
liquid fetal oxygenation, uterus transplantation, extracorporeal
perfusion of the human uterus and animal models. Exclusion cri-
teria were publications in other languages and without clear and
reproducible methods included. The papers selected were critically
assessed, and the results were interpreted and synthesized to design
a prospective strategy to be used towards the further development
of this novel technology. Therefore, the studies mentioned in the
current review are based on reports of the extracorporeal develop-
ment of an embryo/fetus for any length of time and include experi-
ments carried out in human and animal models. Our search
specifically targeted reports of extracorporeal time-lapse preg-
nancy in various species. The outcomes of interest were successful
support of the embryo/fetus from implantation through birth as
well as any intermediate results. No statistical analysis has been
carried out, as the specific topic does not require such analysis.
Results
The results from the literature showed limited published articles on
the topic of ectogenesis. We have identified 21 manuscripts, illus-
trated in Table 1, that were appropriate for the pursuit of this goal.
Artificial endometrium
Since the world’s first ‘test-tube’baby was born in 1978 (Steptoe
and Edwards, 1978), the use of human embryos in research has
become highly controversial ethically and therefore created a sig-
nificant challenge for scientists working in the field. A main object
of debate is ‘the 14-day rule’, which prohibits culturing human
embryos in vitro beyond 14 days or the onset of the primitive
streak, and was proposed over 40 years ago. This regulation has
become a widely accepted bioethical norm and has been intro-
duced into guidelines worldwide. However, recent scientific
advancements and policy debates have put this rule under increas-
ing strain. It has been suggested that it would be technically feasible
to extend the lifespan of in vitro human embryo culture beyond the
current 14-day limit (Morris, 2017). However, there is the need to
obtain specific ethical approval to do so (Warnock, 1985). The cur-
rent 14-day rule on human embryo culture was based on our
understanding of development during the post-implantation
period. This time point marks the end of the period of full devel-
opmental potential and the beginning of gastrulation, when the
embryonic cells begin to differentiate and generate pre-neural cells,
potentially enabling the embryo to experience painful stimuli.
Therefore, this time point is considered the completion of the
pre-embryonic stage and the development of the fetus into a single
human being (Warnock, 1985; Hurlbut et al.,2017). As stated ear-
lier, Morris and colleagues and more recently Hyun and co-authors
reported the successful culture of human embryos for a period that
approached the 14-day limit (Morris, 2017). These results suggest
that this culture period might be successfully prolonged. The
authors noted that an extension of the culture period to 20 or
28 days would permit further investigations into our understand-
ing of early fetal development. An artificial endometrium is essen-
tially epithelial endometrial cells cultured on an artificial three-
dimensional support matrix (e.g. Matrigel®). The support matrix
enables critical processes to occur in the same three-dimensional
orientation as would be encountered in vivo. This goal has already
been achieved by others (Figure 1). Liu described an artificial ute-
rus, which was essentially a culture of epithelial and stromal cells
(Liu, 2017). Similar endometrial cultures and their responses to
steroid hormones have been reported previously by several
research groups (Tseng et al.,1981; Schatz et al.,1984,1994).
Epithelial cells exhibit spontaneous orientation and therefore
may be used to study maternal–embryo interactions (Figures 1
and 2). Ectopic pregnancies (Figure 3) also provide evidence for
the implantation and development of embryos/fetuses in unusual
contexts. These observations may be used to direct additional
research. Of note, while preimplantation mammalian embryos
can be cultured in vitro (Bedzhov and Zernicka-Goetz, 2014), there
are no validated procedures that can be used to culture post-
implantation embryos to study differentiation and organogenesis
(Huang et al.,2020). Therefore, the molecular events that promote
the transformation from pre-gastrulation to organogenesis remain
to be elucidated. Towards this end, a recent study published by
Aguilera-Castrejon and colleagues (Aguilera-Castrejon et al.,
2021) provided the first illustration of the development of post-
implantation mouse embryos outside the uterine environment.
In this study, the authors developed an effective platform that sup-
ported the growth of mouse embryos until day 11. This culture sys-
tem monitored the concentrations of CO
2
and O
2
and also applied
a specific atmospheric pressure, a factor known to be important for
effective oxygen delivery to tissues and therefore appropriate regu-
lation of cell growth (Ueda et al.,2020; Nagamatsu et al.,2019).
Using a combined static and rotating three-dimensional culture
system, the authors elegantly delineated the stages of embryo
development from early gastrulation (day 5.5) to late gastrulation
(day 7.5) and onwards through hindlimb formation (day 11)
(Aguilera-Castrejon et al.,2021).
Uterine transplantation
After several preliminary attempts performed by several authors
(Kisu et al.,2013;Unnoet al.,1993; Kozuma et al.,1999;
Johannesson and Järvholm, 2016), Brännström and collaborators
reported successful uterine transplantation that resulted in fully
successful live births (Brännström et al.,2015). The process
involved the transplant of a uterus that was surgically excised from
a donor with specific vascular characteristics. After delivery, the
transplanted organ was removed. While ultimately successful
and suggested as adequate treatment for a specific subgroup of
infertile women, this was a very complex and expensive procedure.
The extracorporeal perfused human uterus
Methods to be used to provide extracorporeal perfusion of a sur-
gically isolated animal fetus were entirely described in 2016
(Ejzenberg et al.,2016), while that for the human uterus was first
described in 1982 (Bulletti et al.,1986; Figure 4a). Later studies
focused on steroid hormone metabolism (Bulletti et al.,1988a)
and prolonged preservation of uterine tissue (Bulletti et al.,
1987). Interestingly, Greenberg (1954) designed an original perfu-
sion system in 1954. No publications are available regarding that
document and the devices used in the system, most likely because
there was not sufficient technology available at that time
2 Bulletti et al.
https://doi.org/10.1017/S0967199423000175 Published online by Cambridge University Press

Table 1. Characteristics of included studies for country, criteria of inclusion, experimental animal species, design, intervention and results
Study Country Criteria Species Design Intervention Results
Westin
et al.,1958
Sweden Perfusion technique of
fetus
Human Fluid-to-fluid fetal
perfusion
Connection of
vascular fetal system
to perfusion with
oxygenated pre-
warmed medium
Fetuses survived 5–12 h
Zapol et al.,
1969
USA Extrauterine support of
isolated premature lamb
Lamb Fluid-to-fluid fetal
perfusion
Connection of
vascular fetal system
to perfusion with
oxygenated medium
Two days Survival
Steptoe and
Edwards,
1978
UK In vitro fertilization and
embryo transfer
Women Oocytes fertilization
and embryo
development at first
stages in vitro and
embryo transfer
In vitro fertilization
and embryo transfer
(IVF–ET)
Human live birth
Guller et al.,
1984
USA Extracorporeal perfusion
of human placenta
Women Special device with
maternal and fetal
interface
Maternal injection of
steroid precursor and
fetal and maternal
metabolites
evaluation
Characterization of specific
metabolic patterns
Bulletti
et al.,1986
USA Surgical removed
specimens
Women Vascular connection to
extracorporeal
perfusion system
Extracorporeal
perfusion of human
uterus
First human uterus preservation
in vitro
Bulletti
et al.,
1988a;
1988b
Italy Surgical removed
specimens
Women Vascular connection to
extracorporeal
perfusion system
Embryo transfer into
extracorporeal
perfusion of three
human uteri
First human embryo implantation
in vitro
Yasufuku
et al.,1998
Japan Goat extracorporeal
perfusion in an artificial
uterus
Goat Vascular connection to
extracorporeal
perfusion system with
artificial placenta
Extrauterine fetal
incubation
Fetal influence of lung
maturation
Kozuma
et al.,1999
Japan Goat fetuses
disconnected from the
placenta and
reconnected to artificial
placenta
Goat Special designed
artificial placenta
Goat fetuses
connected to artificial
placenta
Disconnection and re-connection
of goat fetuses to an artificial
circulation. EUFI
Pak et al.,
2002
Korea Extrauterine incubation
of fetal goats applying
the extracorporeal
membrane oxygenation
by umbilical artery and
vein
Goat Designed for
extrauterine
incubation of fetal
goat
Fetal goat connected
to vascular perfusion
system
Goat survival in oxygenated
condition
Brännström
et al.,2015
Sweden First live birth after
uterus transplantation
Women Programme for uterine
transplantation and
IVF with embryo
transfer
Pregnancy with
donor uterus
Live birth
Brännström
et al.,2017
Sweden Uterus transplantation Women Uterus transplantation Uterus removal and
donor’s
transplantation
Successful experiment with
transplanted uterus viable
Hellström
et al.,2017
Sweden Uterus bioengineering Women Designed for next
steps in uterus
transplantation
Scaffolds derived
from decellularized
organ/tissues that are
recellularized with
autologous stem cells
Proof of concept
Morris, 2017 USA Embryo cultured in vitro
to 14 days
Human Designed to open the
black box o embryo
development up to
gastrulation
Cultured embryo Description of human embryo
development to 14 days
(Continued)
The ectogenesis 3
https://doi.org/10.1017/S0967199423000175 Published online by Cambridge University Press

(Figure 4b). Human embryos were first implanted into an extra-
corporeal perfused human uterus in 1988 (Bulletti et al.,1988a;
1988b). An extracorporeally perfused human uterus was also used
for studies focusing on the electromechanical assessment of myo-
metrial activity in response to ovarian steroid administration
(Bulletti et al.,1993), aiming to establish the first uterine pass effect
of radioactive hormones administered trans-vaginally (Bulletti
et al.,1997). All of these experiments demonstrated that extracor-
poreal perfusion was able to maintain uterine growth and viability
(Figures 2,4,5,6). Oxygenation through fluid connection and sup-
plementation might be used to sustain a uterus for as long as 4
weeks (Bulletti et al.,1986; Partridge et al.,2017a). Therefore,
the aim of this research was to determine from the current litera-
ture, methods to support a surgically excised uterus by extracorpo-
real perfusion with the mother’s blood. This would be preferable to
a transplantation procedure, as most of the risk associated with the
mother would be avoided. It might also be easier to separate the
vascular connections for complications. Experimental test proce-
dures in other species will be required to test this new promising
design.
Animal and human studies of ectogestation
The literature search revealed that Kuwabara and co-authors man-
aged to preserve a developing goat fetus for 3 weeks in an incubator
that reproduced the uterus with a placenta, amniotic fluid, and
blood supply. Several additional publications have described
encouraging results focusing on efforts to support goat fetus
growth with extracorporeal perfusion (Yasufuku et al.,1998;
Kozuma et al.,1999; Greenspan et al.,2000). Early studies on ecto-
genesis were performed in the 1950s by Westin and colleagues,
who reported attempts to support fetus growth and development
for several animal species using an artificial womb (Westin et al.,
1958). Recently, Partridge and colleagues have reported the suc-
cessful preservation of a live lamb fetus for 4 weeks by extracorpo-
real perfusion in a simple sterile container that replicates the
physiological conditions found in the womb (Partridge et al.,
2017a, supplementary information). The container named a ‘bio-
bag’was made from a transparent, elastic polyethylene film that
facilitated regular monitoring and observation of the fetus. In this
study, infant lambs were delivered by caesarean section when they
Table 1. (Continued )
Study Country Criteria Species Design Intervention Results
Partridge
et al.,2017a
USA Goat fetuses
preservation in an
artificial uterus
Goat Special designed
artificial uterus
Goat fetuses
connected to artificial
uterus
4 weeks goat preservation in an
extracorporeal perfusion system
Partridge
et al.,2017b
USA Goat fetuses
preservation in an
artificial uterus
Goat Special designed
artificial uterus
Goat fetuses
connected to artificial
uterus
4 weeks goat preservation in an
extracorporeal perfusion system
Tiemann
et al.,2020
Sweden Uterus tissue
engineering
Sheep Uterus tissue
engineering:
comparative study of
sheep uterus
decellularization
Building in vitro
organ
Validation of the model
Richardson
et al.,2020
USA Organ-on-chip
technology
Organ
on chip
Designed for feto-
maternal interface
studies
Organ on chip with
special focus on the
maternal-fetal
interface exchange
Model validation
Magalhaes
et al.,2020
USA Bioengineered uterus Rabbit Biodegradable
polymer scaffolds
seeded with
autologous cells to
restore uterine
structure and function
At 6 months post-
implantation, the
cell-seeded
engineered uteri
developed native
tissue-like structures
Rabbits with cell-seeded
constructs had normal
pregnancies –40% –in the
reconstructed segment of the
uterus and supported fetal
development to term and live
birth
Huang
et al.,2020
USA–
China
Intravital images of
mouse embryos
Mouse Implant of window on
mouse embryos
development from day
9.5 to live birth
Removable intravital
window to
manipulate and
detect high resolution
images
Unique description of developing
steps of mouse useful to detect
changes and to manipulate the
processes
Yoshimasa
and
Maruyama,
2021
Japan Bioengineered uterus Humans
and
other
species
Biodegradable
polymer scaffolds
seeded with
autologous stem cells
to restore uterine
structure and function
Different scaffold and
techniques adopted
Validation of various techniques
to reach human bioengineered
uterus
Aguilera-
Castrejon
et al.,2021
Israel Highly effective
platforms for the ex
utero culture of post-
implantation embryos
mouse Platforms for the ex
utero culture of post-
implantation mouse
embryos up to 6 days
Culture system for
mouse embryonic
development in vitro
The establishment of a system
for robustly growing normal
mouse embryos ex utero from
pre-gastrulation to advanced
organogenesis
4 Bulletti et al.
https://doi.org/10.1017/S0967199423000175 Published online by Cambridge University Press

Figure 3. An ectopic (tubal) pregnancy at 9 weeks of development. Fetal survival at
this stage suggests that implantation in different substrates other than the endo-
metrium may lead to successful gestation. Ectopic pregnancies typically result in
weakness and rupture of the tubal wall in response to the aggressive proteolytic activ-
ity of the developing trophoblast.
Figure 4. (a) The uterine perfusion system developed by Bulletti and colleagues
(Bulletti et al.,1986) includes a reservoir of warmed and oxygenated medium that
was forced into the uterine artery lines by a roller pump. (b) The design of an original
perfusion system by Emmanuel M. Greenberg (22 July 1954).
Figure 1. Endometrial epithelial cells that are connected and appropriately oriented
after incubation with a Matrigel platform. The endometrial cells can be cultured on this
matrix when connected to a maternal blood supply by extracorporeal perfusion.
Figure 2. Embryo–mother interaction at implantation both in vitro and in vivo.
The ectogenesis 5
https://doi.org/10.1017/S0967199423000175 Published online by Cambridge University Press

reached a level of lung maturity that was comparable with that of
an extremely premature human baby (i.e. 22–23 weeks of gesta-
tion). The in vitro system provided artificial intravenous nutrition
and included a pump-free oxygenation circuit connected to the
fetus that provided stable hemodynamic, blood gas and oxygena-
tion parameters. Using this artificial platform, eight of 13 lambs
were maintained in a viable state for 20–28 days (Partridge
et al.,2017b). This compelling study outlines the parameters of
a compelling system that could be used for partial ectogenesis
(i.e. ectogestation), as it is capable of supporting this phase of preg-
nancy outside the mother’s body. This technology might be used to
support extremely premature human infants to improve overall
clinical outcomes. At this time, despite the availability of intensive
care technology, preterm infants still exhibit elevated mortality
rates compared with their full-term counterparts (Patel, 2016).
In the near future, one or more ectogestation systems might be
available to support extremely premature infants. These infants
could then undergo extended growth and development in an arti-
ficial womb to improve their long-term health outcomes.
The placenta
Goat and human placental tissue preserved with extracorporeal
perfusion (Zapol et al.,1969) were used to study hormone metabo-
lism (Guller et al.,1984), as a source of components to support fetal
life, as well as to filter maternal components, including immunor-
eactive agents (Unno et al.,1993). A human placenta may continue
to supply nutrients and dispose of waste products if the artificial
uterus surrounding a perfused explanted uterus remains connected
to the mother (Unno et al.,1993,1998; Kozuma et al.,1999; Ochiai,
2000; Westin et al.,1958).
Discussion
Candidates for ectogenesis include women who no longer have a
uterus, women diagnosed with major anatomical abnormalities of
the reproductive tract, including Asherman’s syndrome, and
women with a history of recurrent preterm birth. The group also
includes couples who are considering surrogacy programmes and
Figure 5. (a–e) A glass container that protects
against ultraviolet light contains maternal epi-
thelial endometrial cells in culture with a sup-
porting matrix separated from the blood
supply by a porous membrane (Bulletti et al.,
1987). Circulation of maternal blood from a res-
ervoir (a) is promoted by an artificial heart (b).
Blood provides nutrition to the implantation
side after its oxygenation and filtration by artifi-
cial lungs (c) and kidneys (d), respectively. A sec-
ond artificial kidney (e) provides the fluid
needed to support the filtration process. A com-
puter (f) provides real-time analysis of biochemi-
cal (e.g. pH, pO
2
consumption, and pCO
2
production) and biophysical (e.g. pressures,
and heart rate) parameters. Hand ports are pro-
vided to facilitate the manipulation of the
embryo/fetus. Video attachment: https://
studio.youtube.com/video/mLKb7X2ceVI/edit
6 Bulletti et al.
https://doi.org/10.1017/S0967199423000175 Published online by Cambridge University Press

those who decide to undergo uterine transplantation (Brännström
et al.,2015). This intervention might also benefit women who have
chronic diseases associated with a high risk of fetal malformation
or death, and those who abuse alcohol or drugs. The architects of
this project should include a large collection of scientists, including
those who are familiar with studies carried out on animals and
humans. However, currently, ectogenesis is still in the making.
It is important to note that 62 out of 65 countries with reliable epi-
demiological investigations have announced an increase in pre-
term birth and mortality over the past 20 years. In addition,
>90% of the extremely preterm infants were born in low-income
countries, compared with <10% born in high-income settings.
New approaches to preterm birth are strongly requested to
improve their survival; fluid-to-fluid support may be the solution
and the developing strategy to reach full ectogenesis. As often hap-
pens with technological development, it is believed that the future
validation of ectogenesis and its application worldwide would be of
huge economic interest, especially in those remote countries of
Asia and sub-Saharan Africa (Andres and Day, 2000; Hendler
et al.,2005; Delbaere et al.,2007; Di Renzo et al.,2011; Uzan
et al. 2011; World Health Organization and the March of
Dimes, 2012; Blencowe et al.,2013; American College of
Obstetricians and Gynecologists, 2017; Partridge et al.,2017a;
World Health Organization, 2017; Goldenberg et al.,2008;
National Health Service, online;Preeclampsia Foundation, online).
The main question arising from this review focuses on the need for
systems to support fetal growth outside the maternal womb. To
answer this question, one must first recognize the marked success
of modern reproductive technologies, including in vitro fertiliza-
tion techniques introduced in the 1970s by Edwards (Steptoe
and Edwards, 1978), uterus preservation outside the human body
(Bulletti et al.,1986,1987,1988a), human embryo implantation in
an extracorporeally perfused human uterus (Bulletti et al. 1988b),
intracytoplasmic sperm injection (Palermo et al.,1992), and suc-
cessful human pregnancy and infant birth after human uterus
transplantation (Brännström et al.,2015), and the increased rates
of survival of babies born prematurely. However, currently, several
aspects of reproductive dysfunction remain still unresolved, such
as uterine abnormalities. Approximately 1 in 500 women suffer
from absolute uterine infertility (Johannesson and Järvholm,
2016). Presently, it is not possible for women that lack a uterus
to have biological children without the assistance of a third person
(Brännström et al.,2015; Suzuki, 2014). Other options currently
available include adoption, gestational surrogacy, or uterine trans-
plantation. The latter scenario requires two major surgical proce-
dures (i.e., uterus transplantation with in vitro fertilization;
followed by removal of the donor uterus after completion of the
pregnancy), together with immunosuppressive treatments and
strict bed rest and observation during the pregnancy. The ethical,
religious, social, and economic concerns of the family, as well as the
laws of different countries, contribute to the limited number of sol-
utions currently available to solve these problems. Surrogate moth-
erhood is not permitted in many countries (Kisu et al.,2013) and is
prohibitively expensive in others. While uterine transplantation
Ectogenesis
Pregna ncy stage References
Embryo implantation and
development (weeks 0–2)
Suzuki,
2014;
Morris,
2017
Embryo/fetus development
in vivo (weeks 3–20)*
Extracorporeal survival
(weeks 21–24)
Intensive neonatal care
(weeks 25–40)
Yasufuku et
al., 1998;
Kozuma et
al., 1999;
Greenspan
et al., 2000
Figure 6. Schematic view of potential embryo/fetal
development ex vivo. While there is significant experience
with the ex vivo development of both animal and human
embryos, the path to successful gestation and birth (3–20
weeks) remains to be completed. This effort will require
suitably designed systems and additional experience
with animals of a size and complexity comparable with
humans.
The ectogenesis 7
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provides an alternative to gestational surrogacy, the programme
and procedures involved are complex and quite onerous. Live
donor surgery requires more than 10 h and relies on a critical need
for immunosuppressive therapy to prevent uterine rejection.
Immunosuppression is associated with significant adverse events,
including nephrotoxicity, increased risk of serious infections, and
diabetes (Knight, 2002; Kisu et al.,2013; Ejzenberg et al.,2016;
Hellström et al.,2017). However, two concepts can be taken from
the single published experience using this methodology
(Brännström et al.,2015): (1) a postmenopausal uterus may be
used in this procedure, and (2) embryo implantation rates after
IVF and transfer of the embryo into the transplanted uterus are
encouraging (Palermo et al.,1992). A detailed proposal in support
of this effort was first introduced in 1986 (Steptoe and Edwards,
1978) and again in subsequent years (Bulletti et al.,1986,1987,
1988a). The most recent proposal included more sophisticated
strategies that focused on the design and construction of a bioen-
gineered uterus that could be used for transplantation without
risky donor surgery or the need for immunosuppression
(Palermo et al.,1992).
As physicians, we should progress and try to focus on solutions
to avoid the tragedy of premature birth and death. Fifteen million
infants are born prematurely each year, which is the equivalent of
29 premature infants every minute (Warnock, 1985). Among
these, regrettably, ~3.1 million newborn infants die each year
(Hurlbut et al.,2017). Additionally, premature birth can also have
serious long-term consequences for health and well-being (Morris,
2017), including impaired vision and hearing, neurodevelopmental
disabilities, as well as a long-term increased risks of cardiovascular,
lung, and other non-communicable diseases. There are many
causes of preterm birth, including multiple births (e.g. 60% of twins
are born prematurely) (Tseng et al.,1981; Schatz et al.,1984,1994;
Bedzhov and Zernicka-Goetz, 2014; Johannesson and Järvholm,
2016; Liu, 2017; Nagamatsu et al.,2019; Huang et al.,2020;
Ueda et al.,2020; Aguilera-Castrejon et al.,2021). At this time,
research goals in the field of reproductive medicine are largely
directed at improving our understanding of the causes of preterm
birth, finding solutions to preeclampsia, and exploring how
changes in vaginal microflora might be associated with preterm
labour. However, the medical community does not yet have the
tools needed to reverse this phenomenon. The design of systems
that support ectogenesis is based on several previous advances,
including:
(1) in vitro fertilization (Steptoe and Edwards, 1978);
(2) human embryo implantation in an extracorporeally per-
fused uterus (Bulletti et al.,1988a; 1988b);
(3) perfusion of a human placenta (Zapol et al.,1969; Guller
et al.,1984; Unno et al.,1993;Unnoet al.,1998);
(4) the development of an artificial endometrium (Tseng et al.,
1981; Schatz et al.,1984,1994; Liu, 2017);
(5) sustained pregnancy in a transplanted uterus (Brännström
et al.,2015);
(6) intensive care provided to premature babies and intense
ongoing effort to improve survival and health outcomes
(Unno et al. 1993; Partridge et al.,2017a);
(7) preliminary experiments on different animal species aimed
at evaluating the survival of premature fetuses through their
extracorporeal perfusion in a sterile container (Partridge
et al.,2017a; Figures 5and 6).
Recently, autologous somatic and stem cells have been used to
proliferate decellularized organs/tissues, notably in support of ute-
rine tissue engineering, to sustain propulsive perfusion and an arti-
ficial lung oxygenates filtered blood. (Deane et al.,2013; Alawadhi
et al.,2014; Cervell´o et al.,2015).
Two main approaches are included that can be used for physical
manipulation of the uterus (Figure 5, Video 1). Based on a previous
successful application in humans and other animal species, it
should be possible to maintain embryos/fetuses using this method
for as long as 22 weeks of the full 40 weeks of pregnancy (Figure 6).
The design of a new extracorporeal perfusion system that will
accept and promote the development of an embryo/fetus from
implantation to delivery (Figure 5, Video 1), would provide sup-
port for the remaining 18 weeks of development, thereby complet-
ing ectogenesis (Figure 6). The main indication for future
ectogenesis procedures is candidacy for surrogacy and uterine
transplantation. By current estimates, up to 15% of the reproduc-
tive-aged population is infertile; 3–5% of all cases of infertility are
the result of some form of uterine dysfunction (Lindenman et al.,
1997; Aittomäki et al.,2001; Brinsden, 2003; Bagnoli et al.,2010;
Dempsey, 2013; Practice Committee of the American Society for
Reproductive Medicine, & Practice Committee of Society for
Assisted Reproductive Technology, 2015). Uterine malformations
are diagnosed in 5% of the infertile population, with uterine agen-
esis (diagnosed in 1 in 4500 women) and hypoplasia identified as
the most frequent causes. Müllerian aplasia, including the congeni-
tal absence of the uterus (i.e. Mayer–Rokitansky–Kuster–Hauser
syndrome) is relatively rare with an incidence of 1 per 4000–
5000 newborn girls (Lindenman et al.,1997; Aittomäki et al.,
2001; Brinsden, 2003; Bagnoli et al.,2010; Dempsey, 2013;
Practice Committee of the American Society for Reproductive
Medicine, & Practice Committee of Society for Assisted
Reproductive Technology, 2015). Hysterectomies represent an
additional cause of suffering. The uterus may need to be removed
to excise myomas and to treat abnormal uterine bleeding, adeno-
myosis, postpartum haemorrhage, and uterine cancer. Surrogacy
might also be considered for women diagnosed with severe medical
conditions (e.g., cardiovascular and renal diseases), which might
render a pregnancy life-threatening (Lindenman et al.,1997;
Aittomäki et al.,2001; Brinsden, 2003; Bagnoli et al.,2010;
Dempsey, 2013; Practice Committee of the American Society for
Reproductive Medicine, & Practice Committee of Society for
Assisted Reproductive Technology, 2015). One further indication
is the biological inability to conceive or bear a child, which applies
to same-sex male couples or single men (Dempsey, 2013). In some
countries, gestational carriers may also be considered in cases of
unidentified endometrial factors, for example couples with
repeated unexplained IVF failures despite the development and
replacement of high-quality embryos (Practice Committee of the
American Society for Reproductive Medicine, & Practice
Committee of Society for Assisted Reproductive Technology,
2015). The presence of pollutants and the use of alcohol or other
drugs might also limit the ability to sustain a healthy pregnancy to
term (Practice Committee of the American Society for
Reproductive Medicine, & Practice Committee of Society for
Assisted Reproductive Technology, 2015). A successful artificial
uterus might overcome the need for surrogate mothers for these
patients. Finally, in the near future, once the procedure has been
properly standardized, infants born prematurely will be the pri-
mary beneficiaries of ectogenesis.
8 Bulletti et al.
https://doi.org/10.1017/S0967199423000175 Published online by Cambridge University Press

Ethical concerns
There are many controversies and ethical concerns surrounding
ectogenesis and the use of artificial wombs, as well as the entire
process of uterine transplantation. One of the main questions is
the financial aspect. Ectogenesis and womb graft are very expensive
procedures that might not be necessary if a successful pregnancy
might be achieved using alternative procedures that might be
cheaper and also less invasive. The approaches described in this
review might be chosen when no other options are available, such
as in women who have been diagnosed with severe uterine anoma-
lies, including Asherman’s syndrome, and women with a history of
recurrent preterm birth. Although surrogacy might be considered
as a valid alternative, it is important to note that this practice is
prohibited in many countries, including Arab countries, and it
is also unavailable in other regions due to a ban on providing pay-
ment (Samuels, 2020). Similarly, while surrogacy has recently
become accessible in India (Blazier and Janssens, 2020; Smietana
et al.,2021), this might be unacceptable to many women due to
cultural, moral, religious, or personal factors. In these cases, the
use of an artificial womb may be the only route available to women
who prefer to have their own offspring.
Ectogenesis might be associated with several advantages for
both parents and offspring. This might be a particularly attractive
alternative to elective abortion and/or for those who present with a
high risk of fetal damage during pregnancy (e.g., drug addiction).
In these cases, ectogenesis could provide compelling advantages to
the fetus by providing superior conditions for sustained develop-
ment, including ideally calibrated temperature, oxygenation, and
nutrition in a toxin-free environment.
One of the main concerns discussed regarding the use of an arti-
ficial uterus would be the moral status of the early embryo. Surely,
the debate on this aspect will continue to grow in the future. It is
worth noting that the legal and moral status of embryos and fetuses
has not been universally established, therefore, the application of
ectogenesis generates numerous controversies and tensions allied
to the early stages of human life. There are numerous opinions as to
whether it is appropriate to provide support to human embryos
outside the mother’s body. Some individuals believe that the
human embryo needs full protection starting from the very early
stages following fertilization. Those with actively ‘pro-life’visions
argue that the early embryo/fetus has full moral status and is con-
sidered a full person. These individuals most frequently find ecto-
genesis to be ethically unacceptable, as it is seen as analogous to the
termination of a pregnancy. Another, more gradualist vision con-
siders that the embryo has some moral standing and that its legiti-
macy increases with further development during the pregnancy.
From this standpoint, the embryo/fetus has no sensibility or con-
sciousness and therefore might not be considered as a full human.
Individuals maintaining this viewpoint are typically those who
believe that research can be performed on human embryos until
day 14 (Warnock, 1985). By contrast, individuals who are fully
‘pro-choice’typically perceive the fetus as lacking moral status
and believe that embryos might be provisionally created and used
for research purposes (Bredenoord et al.,2008; Steinbock, 2011;
Dyer, 2012). Disagreement regarding the use of novel reproductive
technologies methods, such as ectogenesis, largely mirrors the
ongoing debate on abortion rights and regulation. Particular atten-
tion must be focused on social and public communication to pre-
vent the dissemination of imprecise or incorrect information that
can lead to confusion and unrealistic expectations.
Conclusion
Ectogenesis involving the development of a human embryo in vitro
up and including live birth remains to be realized. Strong experi-
mental evidence suggests that this may be the only solution that
will relieve the suffering of women who are unable to undergo a
normal pregnancy to term. Current scientific progress supports
22 to 40 weeks of pregnancy outside the human body. Advances
on the path to ectogenesis are moving quickly. The development
of innovative technologies leads us to believe that it may be possible
to provide external support for a full 40 weeks of pregnancy within
a single decade from now. The use of this technology will present
dramatic changes in legal, social, and ethical evaluations of the
entire reproductive process.
Acknowledgements. We thank the great scientist and unforgettable man,
Erlio Gurpide, who believed strongly in this project and included extracorporeal
perfusion of a human uterus among his projects at Mount Sinai Medical Center.
Author contribution. FMB contributed to the conception and designed the
manuscript including the PubMed search. RS and CB wrote sections of the
manuscript. AP researched the literature on preterm birth and fluid-to-fluid
oxygenation system. All authors have read and agreed to the published version
of the manuscript.
Institutional review board statement. All procedures performed in studies
involving human participants were in accordance with the ethical standards of
the institution and with the 1964 Helsinki Declaration and its later
amendments.
Financial support. This research received no specific grant from any funding
agency, commercial or not-for-profit sectors.
Competing interests. The author(s) declare none.
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