Uterus transplantation seems to be a promising method for the causal treatment of absolute uterine factor infertility in women with an absent or non-functional uterus. Since uterus transplantation is still experimental in nature, there are no strict guidelines regarding each step of this comprehensive treatment method. Prior to uterus transplantation, ovarian stimulation and in vitro fertilization are performed on the potential uterus recipient, and the obtained embryos are cryopreserved and stored for the transfers after transplantation when only non-fetotoxic maintenance immunosuppressants are administered. In the first human uterus transplantation study, the start of embryo transfers was set at 12 months after transplantation. Due to the growing experience, especially with early rejections after transplantation and the course of pregnancy, several ongoing studies have experimentally shortened the uterus transplant-to-embryo transfer interval to 6 months. Shortening the total time of immunosuppression administration after uterus transplantation is the main reason for early initiation of embryo transfers after transplantation. However, the safety of an interval of less than one year between uterine transplantation and the first post-transplant embryo transfer should be further studied.
In vitro fertilization – absolute uterine factor infertility – uterus transplantation – Embryo transfer
Uterus transplantation (UTx) is the only option to restore female reproductive anatomy and functionality and seems promising in the treatment of absolute uterine factor infertility (AUFI) in women with absent (congenital, acquired) or non-functional uterus who experience involuntary childlessness, permanent infertility and usually also long-term emotional burden. UTx enables the experience of having a pregnancy and the achievement of genetic, biological and legal parenthood. However, this experimental method has so far only been tested in a few human clinical trials worldwide. UTx is associated with considerable risk and requires conception through in vitro fertilization (IVF) and delivery by cesarean section. It is a transplant of the uterus with surrounding ligaments and supply (uterine) and drainage (uterine and/or ovarian) vessels. To date, only one Swedish experimental UTx study has been completed, starting with the first transplant procedure in 2012 .
Due to the relative infancy of UTx, all steps of this complex method in the treatment of AUFI are still under research, e. g., the onset of post-UTx embryo transfers (ET), robotically assisted minimally invasive uterine graft collection in living donors, ethics and acceptability of living and deceased donors, monitoring of uterine graft rejection after transplantation and during pregnancy. In addition, it is essential to monitor the life of the recipients, their offspring and living donors of the uterus.
A groundbreaking Swedish 9-case UTx study demonstrated the feasibility of the procedure using a live donor uterus (in 2012–2013) and reproductive success with the first live birth after UTx (in 2014). This study was approved by scientific, institutional and ethical authorities, and the study protocol contained clearly defined diagnostic and treatment procedures . In addition, the study was conducted in accordance with the Montreal Criteria for the Ethical Feasibility of Human Uterine Transplantation published by FIGO . Immunosuppressive therapy must be used after transplantation, and uterine rejection and complications related to immunosuppression must be monitored until the graft is removed. Due to the experimental nature of UTx, there are currently no strict guidelines regarding this complex treatment, only recommendations based on the experience of individual centers. Most of the procedures included in the follower’s UTx studies were performed in accordance with the original Swedish UTx trial, but amendments were made in some aspects resulting from unexpected findings and situations. One of these changes was shortening the onset of the first post-transplant ET to achieve pregnancy.
The aim of this study is to explore optimal timing of the first ET after surgically successful UTx and to present rationale for the early start of post-transplant ETs based on current knowledge and experience.
Collection of embryos via IVF and cryopreservation
To date, most uterus transplant recipients worldwide have had Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome with a neovagina created by dilation or surgical methods [4,5]. In potential recipients of a uterus with MRKH syndrome, ovarian stimulation based on a long gonadotropin-releasing hormone agonist protocol and IVF is performed prior to UTx, particularly to rule out other infertility factors that might affect the success of post-transplant fertilization and also to reduce the risk with egg collection after UTx, when the anatomy of the pelvis is altered and the graft uterine vessels anastomosed to the recipient’s external iliac vessels may be damaged during egg retrieval. A minimum of 10 high-quality vitrified day-5 blastocysts were stored before transplantation in women enrolled in the Czech UTx study , but the number of collected frozen embryos before UTx may vary according to the practices of individual centers and legal conditions in different countries, e. g., the minimum number of cryopreserved embryos in the Dallas UTx study was four . Only 3 out of 10 Czech women received one cycle of ovarian stimulation to obtain at least 10 cryopreserved embryos. In 7 women, a second-to-third stimulation was necessary to collect the required number of embryos. Preimplantation genetic testing was not performed on Czech UTx candidates because they were young and had a low risk of aneuploidy. However, preimplantation genetic screening aimed at reducing the time to pregnancy and the risk of miscarriage was performed on some embryos in the Dallas study . In UTx studies, oocytes were fertilized by intracytoplasmic sperm injection. Similar to infertile women with their own uterus, women with MRKH syndrome may develop ovarian hyperstimulation.
The initiation of post-transplant embryo transfers
UTx is performed with the aim to deliver one to two healthy children in each recipient. The issue regarding onset of post-transplant ETs has evolved gradually during the last decade. In anticipation for ET, it is essential to adjust antirejection medication that may not be safe for the period of gestation. Tacrolimus and azathioprine have been shown to be safe during pregnancy, with no increased risk of congenital anomaly. Potentially teratogenic immunosuppressants such as mycophenolate mofetil (MMF) should be stopped a minimum of 6 weeks prior to ET. Although the ET/preg- nancy success rate in the general non-AUFI population varies among assisted reproductive technique centers, successful conception already after the first ET after UTx was recorded in several cases worldwide, e. g., Gothenburg, Sao Paolo, Dallas, and Cleveland, and was encouraging for the followers [8–11].
Although the original Swedish proposal was to start with ETs approximately one year after UTx in line with standard solid organ transplant guidance , the current opinion on the onset of the frozen embryo transfers has changed. Based on individual experience, it currently varies between 3 and 12 months after transplantation . The recommended one-year UTx-to-ET period was based on decades of previous experience with pregnancy after solid organ transplantation, but this recommendation was violated in the first US recipient of a uterus with increased serum creatinine after transplantation, possibly due to the administration of immunosuppressive therapy (tacrolimus). To shorten the post-transplant period with high creatinine levels, the Dallas group decided to perform the first ET at 6 months after UTx. This recipient became pregnant immediately after the first ET and the pregnancy with persistently increased serum creatinine concentrations without preeclampsia was terminated by cesarean section-hysterectomy at 33 weeks and 1 day of gestation . A similar approach to shortening the duration of immunosuppression administration was also chosen in a single Brazilian case with a live birth after a deceased donor UTx . Cases from the US and Brazil opened the debate about the optimal onset of ET after Utx.
The Dallas group recently stated that once menstruation begins, the uterus responds adequately to hormonal stimulation, hence the preparation for ET may start . In addition, this team made another evolutionary step related to the post-transplant onset of ETs: the elimination of MMF, which was part of the post-transplant immunosuppression in all previous uterine recipients worldwide. The maintenance combination of tacrolimus and azathioprine was given immediately after starting immunosuppressive therapy with thymoglobulin and corticosteroids during the transplant procedure. Omitting MMF, the Dallas researchers speculated that ETs could begin as early as 3 months after UTx, if no rejection episodes were detected by then.
Compared to the above approach, Swedish researchers decided to wait 10 months for the first post-transplant ET even in their second UTx study with robotic-assisted donor hysterectomy . Based on their first study with open procurement operations in donors, the Swedish authors preferred to achieve stable serum levels of immunosuppressants and not to start ET early after transplantation as they were concerned about uterine graft rejection [8,13]. Given the recently reported experience of the US research group from Cleveland with a 3-month-long severe graft rejection in a recipient with a uterus from a deceased donor, the Swedish approach appears to be justified even in the era when shortening the originally proposed 1-year waiting period is being tested and preferred by some centers .
The Czech approach to the onset of post-transplant ETs was inspired by the protocol of the first Swedish study with the recommendation to wait approximately one year after UTx to achieve stability of the graft on non-fetotoxic immunosuppressive treatment . Moreover, in 4 out of 7 Czech recipients with a functional uterus, the onset of ETs had to be postponed to 14–18 months after UTx, particularly because of the signs of rejection with the necessity to adjust immunosuppression doses during the first year after transplantation . Additionally, clinically significant stenosis of the uterine-vaginal anastomosis in 4 Czech uterus recipients was a co-factor of later onset of ETs in these cases .
The experience of the first ever mixed cellular/humoral rejection of a uterine graft was recently reported by the Cleveland group . Severe histopathologically confirmed rejection with ulceration occurred during preparation for the first ET at 5 months after UTx without evidence of previous episodes of graft rejection. The rejection was reversed within 3 months with repeated intravenous thymoglobulin. In addition, fetotoxic maintenance immunosuppression (MMF) was administered until the 10 months after transplantation. The first ET was performed one month after elimination of MMF and the recipient immediately became pregnant. The planned cesarean section-hysterectomy was performed at 34 weeks and 2 days of gestation and no further signs of rejection appeared in pregnancy. The above cases from Dallas and Cleveland, US, and Sao Paolo, Brazil, showed that shorter UTx-to-ET interval could be feasible and effective. Shortening of total time of immunosuppression administration after uterus transplantation is the main reason for early initiation of embryo transfers after transplantation. However, the safety of an interval of less than one year between uterine transplantation and the first post-transplant embryo transfer should be further studied.
Some risks related to the recipient‘s post-transplant health, such as premalignant cervical lesions, have been rarely documented. So far, only one recipient of the uterus is known to have moderate cervical dysplasia before pregnancy . From the perspective of an early initiation of ETs to shorten the UTx-to-hysterectomy interval, pre-transplant high-risk HPV testing in donors as well as pre-transplant HPV immunization in recipients could be redundant. Repeated negative Pap smears in a living donor during the preparation period before UTx and one pretransplant negative Pap smear in a deceased donor should be suf- ficient for post-transplant safety of the recipient of the uterus. In addition, the number of suitable donors could be increased because of the relatively high incidence of high-risk HPV positivity in an otherwise healthy population of potential donors of the uterus with a never-before-recorded Pap smear abnormality. If the method of early onset of ETs is adopted, donor HPV testing could be omitted as it reduces the availability of living and deceased donors, particularly if high-risk HPV positivity should be considered as an exclusion criterion. Researchers should monitor post-transplant stability of the uterus, especially to avoid high-grade rejection in pregnancy, which could pose a serious problem if it occurs.
Since the total number of uterine transplants performed to date has been less than 100 worldwide, and only a part of them has been described in detail, we should be cautious in making premature speculative conclusions, including the timing of the first ET after transplantation . Since the early onset of ETs is fundamentally different from previous clinical practice and long-term recommendations in solid organ transplant recipients , the optimal timing of the first ET after UTx should be continuously studied and monitored in further experimental studies on this topic.
Similar to the development of guidelines for solid organ transplants and methods of assisted reproduction, UTx guidelines are also gradually evolving with increasing experience. This development is mainly based on the results of UTx studies registered in scientific databases. The idea of an early post-transplant start of ETs seems promising but is still experimental. Protocol modifications of UTx studies related to the onset of post-transplant ETs could be a reason to extend the experimental period until UTx is implemented in clinical practice, as the comparison of the complete results of different studies could be more difficult due to the inconsistency of approaches in individual research centers.
R. Chmel 0000-0003-2087-4656
M. Nováčková 0000-0003-2531-4009
M. Čekal 0000-0003-4537-325X
J. Matěcha 0000-0002-3813-4720
Z. Pastor 0000-0002-1425-5982
Submitted/Doručeno: 12. 7. 2022
Accepted/Přijato: 20. 7. 2022
Assoc. Prof. Roman Chmel, MD, PhD, MHA
Department of Obstetrics and Gynecology
Second Faculty of Medicine
Charles University and
Motol University Hospital
V Úvalu 84
150 06 Prague
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