A new era in reproductive medicine: consequences of third-party oocyte donation for maternal and fetal health

Pregnancies through oocyte donation. A mini review of pathways involved in placental dysfunction

Pregnancies resulting from assisted reproductive techniques (ART) are increasingly prevalent worldwide. While most pregnancies conceived through in-vitro fertilization (IVF) progress without complications, mounting evidence suggests that these pregnancies are at a heightened risk of adverse perinatal outcomes. Specifically, IVF pregnancies involving oocyte donation have garnered attention due to numerous reports indicating an elevated risk profile for pregnancy-related complications within this subgroup of patients. The precise mechanisms contributing to this increased risk of complications remain incompletely understood. Nonetheless, it is likely that they are mediated by an abnormal immune response at the fetal-maternal interface. Additionally, these outcomes may be influenced by baseline patient characteristics, such as the etiology of infertility, absence of corpus luteum, and variations in endometrial preparation protocols, among other factors. This review aims to succinctly summarize the most widely accepted mechanisms that potentially contribute to the onset of placental dysfunction in pregnancies conceived through oocyte donation.

Inflammatory placental lesions are specifically observed in healthy oocyte donation pregnancies with extreme fetal-maternal incompatibility

INTRODUCTION

Oocyte donation (OD) pregnancy is a risk factor for pre-eclampsia (PE). Due to a higher extent of fetal-maternal human leukocyte antigens (HLA) mismatching in OD pregnancies compared to naturally conceived (NC) and in vitro fertilization (IVF) pregnancies, the immune response in OD placentas is probably divergent and affects clinical outcomes. We hypothesized that placental pathology varies among diverse pregnancy conditions and is related to fetal-maternal HLA incompatibility.

METHODS

Placental lesions were scored in four patient groups: OD-PE (n = 16), OD-healthy (n = 37), NC-PE (n = 45), and IVF-healthy (n = 17). All combinations were genotyped for HLA-A, -B, -C, -DR, and -DQ to calculate fetal-maternal HLA mismatches. Placentas showing chronic deciduitis with plasma cells were immunofluorescently stained with CD138 and the anti-inflammatory cytokine interleukin-10 (IL-10).

RESULTS

The distribution and severity of placental lesions varied among groups. The OD-healthy group had the highest inflammation score and greatest extent of chronic deciduitis with plasma cells (p < 0.05). However, the majority of CD138+ plasma cells (90%) in OD-healthy group expressed IL-10, in contrast to the OD-PE group (58%). The OD-healthy group was separated into semi-allogeneic (≤5 HLA mismatches) and fully allogeneic (>5 mismatches) subgroups. The elevated inflammatory pathology score and chronic deciduitis with plasma cells were found more often in the HLA-class-I fully allogeneic OD-healthy group than the IVF-healthy group (p < 0.05).

DISCUSSION

Placental inflammatory lesions are most often present in uncomplicated OD pregnancies. Immune cells that infiltrate these lesions might play an immunosuppressive role to protect OD pregnancies from complications when facing a higher extent of fetal-maternal HLA mismatching.

Pregnancy by Oocyte Donation: Reviewing Fetal-Maternal Risks and Complications

Oocyte donation (OD) has greatly improved over the last three decades, becoming a preferred practice of assisted reproductive technology (ART) for infertile women wishing for motherhood. Through OD, indeed, it has become possible to overcome the physiological limitation due to the ovarian reserve (OR) exhaustion as well as the poor gamete reliability which parallels the increasing age of women. However, despite the great scientific contribution related to the success of OD in the field of infertility, this practice seems to be associated with a higher rate of major risky events during pregnancy as recurrent miscarriage, infections and placental diseases including gestational hypertension, pre-eclampsia and post-partum hemorrhage, as well as several maternal-fetal complications due to gametes manipulation and immune system interaction. Here, we will revisit this questioned topic since a number of studies in the medical literature focus on the successful aspects of the OD procedure in terms of pregnancy rate without, however, neglecting the risks and complications potentially linked to external manipulation or heterologous implantation.

Evidence-Based Pre-Pregnancy Counseling for Oocyte Donation Pregnancies: a Systematic Review and Guide for Physicians

It is well known that oocyte donation (OD) pregnancies are associated with higher complication rates compared to autologous pregnancies. However, evidence-based information for pre-pregnancy counseling designed for health care workers is scarce. Therefore, a systematic literature search was performed to find articles that address pre-pregnancy counseling before OD.A systematic search was conducted in September 2020 in various databases, including PubMed and Embase. Nine (systematic) reviews and meta-analyses were included that reported on pre-pregnancy advice in OD pregnancies.Studies are consistent in documenting a higher risk for hypertensive disorders, cesarean section, preterm birth, postpartum hemorrhage, and low birth weight. Based on these complications, pre-pregnancy advice is mentioned in all included systematic reviews to prevent complications in the next pregnancy. All studies recommend counseling women on the increased risk of complications during OD pregnancy. Other recommendations include the prophylactic use of aspirin in pregnancy and restriction to single embryo transfer. Individualized appropriate surveillance and management strategies should be considered for every patient achieving pregnancy by OD.In conclusion, we provide a summary of the most important outcomes in OD pregnancies, and thereby offer a guide for pre-pregnancy counseling.

Immune Tolerance of Embryo Implantation and Pregnancy: The Role of Human Decidual Stromal Cell- and Embryonic-Derived Extracellular Vesicles

Embryo–endometrial communication plays a critical role in embryo implantation and the establishment of a successful pregnancy. Successful pregnancy outcomes involve maternal immune modulation during embryo implantation. The endometrium is usually primed and immunomodulated by steroid hormones and embryo signals for subsequent embryo implantation and the maintenance of pregnancy. The roles of extracellular vesicles (EVs) and microRNAs for the embryo–maternal interactions have been elucidated recently. New evidence shows that endometrial EVs and trophectoderm-originated EV cargo, including microRNAs, proteins, and lipids in the physiological microenvironment, regulate maternal immunomodulation for embryo implantation and subsequent pregnancy. On the other hand, trophoblast-derived EVs also control the cross-communication between the trophoblasts and immune cells. The exploration of EV functions and mechanisms in the processes of embryo implantation and pregnancy will shed light on a practical tool for the diagnostic or therapeutic approaches to reproductive medicine and infertility.

Horizontal inequity in the utilisation of Continuum of Maternal Health care Services (CMHS) in India: an investigation of ten years of National Rural Health Mission (NRHM)

BACKGROUND

Continuum of Maternal Health Care Services (CMHS) has garnered attention in recent times and reducing socio-economic disparity and geographical variations in its utilisation becomes crucial from an egalitarian perspective. In this study, we estimate inequity in the utilisation of CMHS in India between 2005 and 06 and 2015-16.

METHODS

We used two rounds of National Family Health Survey (NFHS) - 2005-06 and 2015-16 encompassing a sample size of 34,560 and 178,857 pregnant women respectively. The magnitude of horizontal inequities (HI) in the utilisation of CMHS was captured by adopting the Erreygers Corrected Concentration indices method. Need-based standardisation was conducted to disentangle the variations in the utilisation of CMHS across different wealth quintiles and state groups.  Further, a decomposition analysis was undertaken to enumerate the contribution of legitimate and illegitimate factors towards health inequity.

RESULTS

The study indicates that the pro-rich inequity in the utilisation of CMHS has increased by around 2 percentage points since the implementation of National Rural Health Mission (NRHM), where illegitimate factors are dominant. Decomposition analysis reveals that the contribution of access related barriers plummeted in the considered period of time. The results also indicate that mother's education and access to media continue to remain major contributors of pro-rich inequity in India. Considering, regional variations, it is found that the percentage of pro-rich inequity in high focus group states increased by around 3% between 2005 and 06 and 2015-16. The performance of southern states of India is commendable.

CONCLUSIONS

Our study concludes that there exists a pro-rich inequity in the utilisation of CMHS with marked variations across state boundaries. The pro-rich inequity in India has increased between 2005 and 06 and high focus group states suffered predominantly. Decentralisation of healthcare policies and  granting greater power to the states might lead to equitable distribution of CMHS.

The association between chronic deciduitis and preeclampsia

Chronic deciduitis (CD) is slight inflammation of the decidua found during pregnancy. The cause of preeclampsia is thought to be placental hypoplasia, and various theories have been proposed to explain the detailed mechanism; however, its association with decidual inflammation is unclear. A retrospective case control study was conducted in a single university. Subjects were cases who delivered by cesarean section between January 1, 2013 and June 30, 2020 and whose placentas were pathological assessed. CD was diagnosed by CD138 immunostaining of placental decidua tissue, and the perinatal prognosis and incidences of hypertensive disorder of pregnancy and preeclmpsia were examined according to the presence or absence of CD. A logistic regression analysis was performed to evaluate the association between preeclampsia and 11 explanatory variables (10 patient or perinatal background factors and CD). The study population included 76 patients (non-CD, n = 54; CD, n = 22). The rate of preeclampsia was significantly higher in the CD group (P = 0.0006). Patients with CD gave birth at a significantly earlier gestational age (P=0.040) with a lower birth weight (P = 0.001), and a higher rate of LFD (P = 0.005). The Apgar scores at 1 and 5 min and umbilical artery pH were lower (P = 0.0003, 0.021 and 0.002, respectively) in the CD group. The logistic regression analysis revealed that CD was positively associated with preeclampsia. A retrospective examination of the placenta found that patients with CD had a significantly higher incidence of preeclampsia and CD is considered to be a factor that is associated with poor perinatal outcomes.

Uncomplicated oocyte donation pregnancies display an elevated CD163-positive type 2 macrophage load in the decidua, which is associated with fetal-maternal HLA mismatches

PROBLEM

The embryo of an oocyte donation (OD) pregnancy is completely allogeneic to the mother, which may challenge the maternal immune system to tolerize the fetus. Decidual macrophages are essential in maintaining a healthy pregnancy, and type 2 macrophages may exhibit immune suppressive activity. We hypothesized that the composition of decidual macrophages is different between uncomplicated OD pregnancies and non-OD in vitro fertilization (IVF) pregnancies, and is related to fetal-maternal incompatibility.

METHOD OF STUDY

Women with uncomplicated pregnancy were enrolled: 25 singleton OD pregnancies and 17 non-OD IVF pregnancies. The extent of immunohistochemical staining of CD14 (pan-macrophage marker) and CD163 (type 2 macrophage marker) in both decidua basalis and parietalis was quantitated by digital image analysis. Maternal and fetal DNA was typed for human leukocyte antigen (HLA)-A, -B, C, -DRB1, and -DQB1, and fetal-maternal HLA mismatches were calculated.

RESULTS

OD pregnancies showed a higher percentage of CD163+ staining (P = .040) and higher CD163/CD14 ratio (P = .032) in the parietalis than non-OD IVF. The OD group was separated into a semi-allogeneic group (≤5 fetal maternal HLA mismatches) and a fully allogeneic group (> 5 mismatches). The HLA-fully-allogeneic OD group, but not the HLA-semi-allogeneic OD group, showed significantly elevated CD163/CD14 ratio in the parietalis compared with the non-OD IVF group (P < .05).

CONCLUSIONS

Uncomplicated OD pregnancies display a higher CD163-positive cell fraction in the total decidual macrophage population compared to autologous pregnancies, which may suggest that a local type 2 macrophage-related mechanism is needed to compensate for the higher fetal-maternal HLA mismatch load.

The role of decidual regulatory T cells in the induction and maintenance of fetal antigen-specific tolerance: Imbalance between regulatory and cytotoxic T cells in pregnancy complications

Fetal antigen-specific tolerance is important for maintaining allogeneic pregnancies. Maternal conventional T cells recognize fetal antigens; however, regulatory T (Treg) cells suppress immune reactions against the fetus. Fetal antigen-specific Treg cells are induced in the decidua upon contact with antigen-presenting cells and extravillous trophoblasts (EVTs). Functional alteration of cytotoxic T cells (CTLs) in the decidua also contributes to maintaining the pregnancy. Reduced, dysfunctional, and imbalanced Treg cell distribution likely contributes to the pathogenesis of pregnancy complications, such as miscarriage and preeclampsia. Recent studies have revealed differences in Treg cell characteristics during preeclampsia and miscarriage. Treg cell reduction in the decidua is likely associated with miscarriage. Insufficient expansion of fetal antigen-specific Treg cells in the decidua probably plays a role in preeclampsia pathogenesis. In addition, the balance between Treg cell-mediated tolerance and functional alteration of CTLs is important. Further investigations of functional molecules in Treg cells will contribute to the development of immunotherapy for pregnancy complications.

Cytokine imbalance at materno-embryonic interface as a potential immune mechanism for recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is a prominent reproductive disease that distresses about 2%-5% of couples. RPL is the loss of two or more successive spontaneous pregnancies prior to the 20th week of embryo development. The commencement of pregnancy necessitates implantation of the embryo into responsive maternal decidua synchronized with the process of placentation, decidual and myometrial trophoblast incursion as well as refashioning of spiral blood arteries of uterus. The collapse of any of the processes fundamental for pregnancy success may result into an array of pregnancy problems including spontaneous pregnancy loss. Endometrium of human female manufactures an extensive range of cytokines during the proliferative and secretory stage of the menstrual cycle. These endometrial cytokines are thought as major players for making the uterus ready for embryo implantation and placental development during pregnancy. Decidual cytokines regulate the invasion of trophoblast and remodeling of spiral arteries as well as take part in immune suppression to accomplish the pregnancy. Deterrence of maternal rejection of embryo needs a regulated milieu, which takes place essentially at the embryo-maternal interface and the tissues of the uterus. The reasons of RPL remain anonymous in a large number of cases that lead to difficulties in management and severe trauma in couples. Cytokine modulatory therapies have been shown promising for preventing RPL. Further study of novel factors is wanted to establish more effective RPL treatment protocols. The present study aims to review the outcome of cytokine breach at materno-embryonic interface and the efficacy of cytokine modulatory therapies in RPL.

Decreased expression of ligands of placental immune checkpoint inhibitors in uncomplicated and preeclamptic oocyte donation pregnancies

Oocyte donation (OD) pregnancies are characterized by a complete immunogenetic dissimilarity between mother and fetus, which requires enhanced immunoregulation compared to naturally conceived (NC) pregnancies. The trophoblast expresses co-inhibitory ligands crucial for regulation of the maternal T cell response. Therefore, we studied the role of placental immune checkpoint inhibitors for the establishment of fetal tolerance and their relation to the development of preeclampsia in OD compared to NC pregnancies. Placental tissue from uncomplicated OD (n = 21) and NC (n = 21) pregnancies, and OD (n = 9) and NC (n = 15) pregnancies complicated with preeclampsia were studied. Protein expression of co-inhibitory ligands PD-L1 and CD200 was double blind semi-quantitatively determined by immunohistochemistry. Messenger RNA expression of PD-L1, CD200 and indoleamine 2,3-dioxygenase (IDO) was determined using qPCR. Decreased PD-L1 and CD200 protein expression and increased IDO mRNA expression was observed in uncomplicated OD versus NC pregnancies (all p < 0.05). CD200 protein expression was positively correlated with PD-L1 expression in all groups, with the number of HLA total mismatches and with HLA class I mismatches in uncomplicated OD cases (all p < 0.05). Preeclamptic cases showed lower PD-L1 protein and CD200 protein and mRNA expression in OD compared to NC pregnancies (all p < 0.05). This study shows that signaling by co-inhibitory PD-L1 and CD200 and by immunosuppressive IDO is altered in the placenta of OD pregnancies, suggesting a contribution to the higher risk for preeclampsia. These insights provide future prospects in unraveling the immune paradox of oocyte pregnancy, which are applicable for better risk management and treatment of uncomplicated and preeclamptic pregnancies.

Evaluation of T cell cytokines and their role in recurrent miscarriage

Recurrent miscarriage (RM) is defined as two or more consecutive pregnancy losses that affect approximately 5% of conceived women worldwide. RM is a multi-factorial reproductive problem and has been associated with parental chromosomal abnormalities, embryonic chromosomal rearrangements, uterine anomalies, autoimmune disorders, endocrine dysfunction, thrombophilia, life style factors, and maternal infections. However, the exact cause is still undecided in remaining 50% of cases. Immunological rejection of the embryo due to exacerbated maternal immune reaction against paternal embryonic antigens has been set forth as one of the significant reason for RM. The accurate means that shield the embryo during normal pregnancy from the attack of maternal immune network and dismissal are inadequately implicit. However, it is suggested that the genetically irreconcilable embryo escapes maternal immune rejection due to communication among many vital cytokines exuded at maternal-embryonic interface both by maternal and embryonic cells. Previous investigations suggested the Th1/Th2 dominance in altered immunity of RM patients, according to which the allogenic embryo flees maternal T cell reaction by inclining the Th0 differentiation toward Th2 pathway resulting into diminished pro-inflammatory Th1 immunity. However, recently pro-inflammatory Th17 cells and immunoregulatory Treg cells have been discovered as essential immune players in RM besides Th1/Th2 components. Cytokines are believed to develop a complicated regulatory network so as to establish a state of homeostasis between the semi-allogenic embryo and the maternal immune system. However, an adverse imbalance among cytokines at maternal-embryonic interface perhaps due to their gene polymorphisms may render immunoregulatory means not enough to re-establish homeostasis and thus may collapse pregnancy.

Risk of Preeclampsia and Adverse Pregnancy Outcomes after Heterologous Egg Donation: Hypothesizing a Role for Kidney Function and Comorbidity

BACKGROUND AND OBJECTIVES

Preeclampsia (PE) is a risk factor for kidney diseases; egg-donation (ED) increasingly used for overcoming fertility reduction, is a risk factor for PE. CKD is also a risk factor for PE. However, kidney function is not routinely assessed in ED pregnancies. Objective of the study is seeking to assess the importance of kidney function and maternal comorbidity in ED pregnancies.

DESIGN, SETTING, PARTICIPANTS AND MEASUREMENTS

DESIGN

retrospective observational study from clinical charts.

SETTING

Sant'Anna Hospital, Turin, Italy (over 7000 deliveries per year).

SELECTION

cases: 296 singleton pregnancies from ED (gestation > 24 weeks), who delivered January 2008-February 2019. Controls were selected from the TOrino Cagliari Observational Study (1407 low-risk singleton pregnancies 2009-2016).

MEASUREMENTS

Standard descriptive analysis. Logistic multiple regression analysis tested: PE; pregnancy-induced hypertension; preterm delivery; small for gestational age; explicatory variables: age; BMI; parity; comorbidity (kidney diseases; immunologic diseases; thyroid diseases; other). Delivery over time was analyzed according to Kaplan Meier; ROC (Relative Operating Characteristic) curves were tested for PE and pre-term delivery, employing serum creatinine and e-GFR as continuous variables. The analysis was performed with SPSS v.14.0 and MedCalc v.18.

RESULTS

In keeping with ED indications, maternal age was high (44 years). Comorbidity was common: at least one potential comorbid factor was found in about 40% of the cases (kidney disease: 3.7%, immunologic 6.4%, thyroid disease 18.9%, other-including hypertension, previous neoplasia and all other relevant diseases-10.8%). No difference in age, parity and BMI is observed in ED women with and without comorbidity. Patients with baseline renal disease or "other" comorbidity had a higher risk of developing PE or preterm delivery after ED. PE was recorded in 23% vs. 9%, OR: 2.513 (CI 1.066-5.923; p = 0.039); preterm delivery: 30.2% vs. 14%, OR 2.565 (CI: 1.198-5.488; p = 0.044). Limiting the analysis to 124 cases (41.9%) with available serum creatinine measurement, higher serum creatinine (dichotomised at the median: 0.67 mg/dL) was correlated with risk of PE (multivariate OR 17.277 (CI: 5.125-58.238)) and preterm delivery (multivariate OR 2.545 (CI: 1.100-5.892).

CONCLUSIONS

Within the limits of a retrospective analysis, this study suggests that the risk of PE after ED is modulated by comorbidity. While the cause effect relationship is difficult to ascertain, the relationship between serum creatinine and outcomes suggests that more attention is needed to baseline kidney function and comorbidity.

Decidual immune cells: Guardians of human pregnancies

During human pregnancy, trophoblast cells, the main cellular component of the placenta, invade deeply into uterine blood vessels and the modified endometrium (decidua). Hence, the maternal immune system must adapt to it. A successful pregnancy requires the tolerance of genetically different (allogenic) cells while the mother's immune competence is maintained. This tolerance is ensured through multiple overlapping and occasionally redundant innate and adaptive immune mechanisms. The present article aims to provide a broad overview on uterine immune cell components and the phenotypical and functional changes that they experience during pregnancy. Particularly, we seek to highlight very recent findings in functional adaptations to pregnancy in immune cell populations encountered in the decidua. These adaptations not only ensure tolerance to allogenic trophoblast cells but also promote optimal placental and fetal growth, simultaneously endeavoring to maintain immune surveillance to provide defense against infections.

New Paradigm in the Role of Regulatory T Cells During Pregnancy

Semi-allogenic fetuses are not rejected by the maternal immune system because feto-maternal tolerance induced by CD4⁺CD25⁺FoxP3⁺ regulatory T (Treg) cells is established during pregnancy. Paternal antigen-specific Treg cells accumulate during pregnancy, and seminal plasma priming plays an important role in expanding paternal antigen-specific Treg cells in mouse models. Although paternal-antigen specific Treg cells have not been identified in humans, recent studies suggest that antigen-specific Treg cells exist and expand at the feto-maternal interface in humans. Studies have also revealed that reduction of decidual functional Treg cells occurs during miscarriage with normal fetal chromosomal content, whereas insufficient clonal expansion of decidual Treg cells is observed in preeclampsia. In this review, we will discuss the recent advances in the investigation of mechanisms underlying Treg cell-dependent maintenance of feto-maternal tolerance.

Reactive Species Interactome Alterations in Oocyte Donation Pregnancies in the Absence and Presence of Pre-Eclampsia

In pregnancy, maternal physiology is subject to considerable adaptations, including alterations in cardiovascular and metabolic function as well as development of immunological tolerance towards the fetus. In an oocyte donation pregnancy, the fetus is fully allogeneic towards the mother, since it carries both oocyte donor antigens and paternal antigens. Therefore, oocyte donation pregnancies result in an immunologically challenging pregnancy, which is reflected by a higher-than-normal risk to develop pre-eclampsia. Based on the allogeneic conditions in oocyte donation pregnancies, we hypothesized that this situation may translate into alterations in concentration of stable readouts of constituents of the reactive species interactome (RSI) compared to normal pregnancies, especially serum free thiols, nitric oxide (NO) and hydrogen sulfide (H₂S) related metabolites. Indeed, total free thiol levels and nitrite (NO₂-) concentrations were significantly lower whereas protein-bound NO and sulfate (SO₄2-) concentrations were significantly higher in both oocyte donation and naturally conceived pregnancies complicated by pre-eclampsia. The increased concentrations of nitrite observed in uncomplicated oocyte donation pregnancies suggest that endothelial NO production is compensatorily enhanced to lower vascular tone. More research is warranted on the role of the RSI and bioenergetic status in uncomplicated oocyte donation pregnancies and oocyte donation pregnancies complicated by pre-eclampsia.

Preliminary evidence of a paternal-maternal genetic conflict on the placenta: Link between imprinting disorder and multi-generational hypertensive disorders

There has been great research progress on hypertensive disorders in pregnancy (HDP) in the last few decades. Failure of placentation, especially a lack of uterine spiral artery remodeling, is the main pathological finding of HDP. Currently, members of the vascular endothelial growth factor family are used as markers for the early prediction of onset of HDP. Epidemiologic research has also shown that HDP can have effects on the next generation infants, representing a Development Origins of Health and Disease-related disease. However, the precise pathogenic mechanism and the effect of HDP on the offspring remain unclear. The group of strong pro-inflammatory molecules known as "danger signals" have been shown to be released from the placental trophoblast surface and increase in the maternal circulation in HDP, which are then possibly transported into the fetal circulation. These signals, including fatty acids or adipocytokines, may alter the offspring's health in later life. Moreover, a hypoxic condition alters placental methylation, and the change may be passed onto the fetus. Although the genetic origin of the disease is still unknown, a hypothesis has been put forward that a paternal-maternal genetic conflict, mainly at imprinting lesion sites, may be a key factor for disease initiation. In particular, an imbalance in paternal and maternal factors may impede proper placentation, trophoblast invasion, decidualization or immune moderation so as to achieve better nutrition for the fetus (paternal) versus ensuring safe delivery and further pregnancy (maternal). Here, we review this research progress on HDP and focus on this novel genetic conflict concept, which is expected to provide new insight into the cause, pathophysiology, and multi-generational effects of HDP.

Safety and efficiency of oocyte vitrification

As the oocyte is the starting point for a new life, artificial reproductive technology (ART) techniques should not affect the (ultra) structural and functional integrity, or the developmental competence. Oocyte vitrification -one of the most significant achievements in human ART during the past decade- should therefore be a safe and efficient technique. This review discusses the principles and developments of the existing and future techniques, applications possibilities and safety concerns. The broad range of vitrification media and devices that are currently available, show differences in their effects on the oocyte ultrastructure and preimplantation development. It is not yet fully decided whether this has an influence on the obstetric and neonatal outcome, since only limited information is available with different media and devices. For autologous oocytes, the obstetric and neonatal outcomes appear promising and comparable to pregnancies obtained with fresh oocytes. This however, is not the case for heterologous fresh or vitrified oocytes, where the immunological foreign foetus induces adverse obstetric and neonatal outcomes. Besides the oocyte vitrification process itself, the effect of multiple stimulations (for oocyte banking or for oocyte donors), seems to influence the possibility to develop gynaecological cancers further in life. Automated vitrification/warming should offer a consistent, cross-contamination free process that offers the highest safety level for the users. They should also produce more consistent results in survival, development and clinical pregnancies between different IVF clinics.