Introduction

Allogeneic hematopoietic stem cell transplantation (HSCT) is a highly effective and potentially curative therapy in pediatric patients, applicable to high-risk malignant hematological disorders as well as severe non-malignant conditions, including hemoglobinopathies, inborn errors of immunity, aplastic anemia, and specific metabolic diseases [1, 2]. Autologous HSCT serves as a consolidation therapy for several poor-prognosis solid tumors, such as N-myc–amplified and/or stage IV neuroblastoma and certain brain tumors [1, 3]. Moreover, hematopoietic stem cell–based gene therapy has recently expanded therapeutic options for inherited diseases, such as leukodystrophies and hemoglobinopathies [4].

Approximately 75–80% of all pediatric allogeneic HSCTs, as well as nearly all autologous HSCTs and gene therapy procedures, employ myeloablative conditioning regimens that combine either total body irradiation (TBI) or alkylating agents [5]. These regimens are associated with a high risk of gonadal damage in both male and female patients, posing a serious threat to future fertility [6]. The individual risk must be assessed comprehensively, considering prior treatments, the specific composition and intensity of the conditioning regimen, the underlying disease, as well as the patient’s sex, age, and pubertal stage.

Fertility impairment remains one of the principal long-term adverse consequences impacting quality of life in HSCT survivors. Therefore, comprehensive and transparent counseling regarding fertility risks and available preservation options is essential and, in several countries, legally required.

This paper aims to provide an updated overview of current strategies for FP in the pediatric HSCT setting and includes recommendations from a subgroup of the Westhafen Intercontinental Group, which is comprised of leaders from the Center for International Blood and Marrow Transplant Research (CIBMTR) Morbidity, Recovery and Survivorship Working Committee and the Pediatric Diseases Working Party of the European Society for Bone and Marrow Transplantation (EBMT). Consensus was achieved through representatives from each of the groups that were tasked with paper planning, writing, and editing. By summarizing contemporary evidence and practices and explicitly recommending the implementation of FP measures, we seek to support clinicians in delivering equitable, informed, and accessible FP counseling and care for all eligible patients.

Counseling and decision making

Providing fertility counseling during the pre-HSCT phase is challenging for transplant physicians. While having to deliver concrete facts and figures about HSCT-related risks, they must also honor the patient’s autonomous wishes, ideas and individual judgments to guarantee certified informed consent, in the specific triangular pediatric setting. Patients and their parents must be informed about the indication for transplantation, the procedures involved, the acute side effects, the expected long-term outcomes, and the risk of death. Mentioning possible long-term side effects, including fertility issues, often increases concerns about the procedure, even though it suggests long-term survival. Among the information received pre-transplant, the risk of infertility can be amongst the most devastating [7].

Various FP options can be tailored to patients and available resources [8]. It is crucial to provide clear information about standard and experimental options for preservation. Obtaining informed consent is mandatory for all FP procedures, with special attention for minors. This requires parental consent and, whenever possible, the child’s assent. When experimental FP techniques are considered, their investigational nature, potential risks, and uncertainties must be clearly explained, and such interventions should only be offered under approved clinical research protocols. Several conditions for which transplant is offered may have specific procedural concerns that patients and clinicians should consider (Table 1). The concepts of fertility, childbearing and parenthood are strongly influenced by culture [9]. Therefore, an individual’s opinions on semen preservation, masturbation, electroejaculation and ovarian or testicular biopsies may differ greatly depending on ethnic and cultural background.

Table 1 Restrictions on fertility preservation measures in special situations.
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In children, HSCT is often used as treatment for genetic diseases. When discussing fertility-preserving measures, the possible transmission of underlying diseases, especially X-linked diseases, should be considered and mentioned in the counseling interview. Genetic counselling should be proposed in parallel.

Counselling should include the following [1]. An infertility risk assessment, considering the patient’s underlying disease, age, pre-SCT treatment and planned conditioning, as well as any known co-morbidities that may impact fertility regardless of HSCT [2]. An overview of established and experimental FP techniques, tailored to the patient’s sex, age, and underlying disease [3]. An in-depth discussion with the patient and their family about the most suitable preservation strategies, as well as a discussion of the risks and side effects associated with the procedure and the prospects and costs for fertility restoration.

It is strongly recommended to offer counselling related to FP opportunities to every patient receiving HSCT as part of the pre-SCT workup. Psychological support should accompany counseling, as FP decisions can be emotionally complex. Comprehensive care is best delivered through a multidisciplinary team including pediatric oncologists/hematologists, nurse navigators, reproductive specialists, endocrinologists, and psychologists.

Fertility preservation techniques: biological and medical considerations

Pre-Pubertal FP

Females

For prepubertal girls, ovarian tissue cryopreservation (OTC) is currently the only available FP option, as they do not yet produce mature oocytes (Fig. 1). The procedure involves laparoscopic removal of ovarian tissue, which is subsequently dissected and cryopreserved. Depending on the underlying disease, this tissue can be transplanted back either orthotopically or heterotopically to restore both endocrine and exocrine ovarian function and fertility, though the half-life of the reimplanted ovarian tissue is limited to a few years. OTC has resulted in live births from cryopreserved tissue from adults and adolescents [10,11,12,13,14]. However, outcome data from tissues stored for prepubertal patients remain limited due to the time between tissue harvesting and potential use [15]. Experimental options, such as in vitro folliculogenesis to obtain mature oocytes from prepubertal ovarian tissue, are under active investigation but are not yet clinically established [16,17,18].

Fig. 1
Fig. 1The alternative text for this image may have been generated using AI.
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Various FP options exist for females depending on menarchal status, HSCT indication (i.e., malignant vs. non-malignant), available time for FP prior to starting gonadotoxic therapies, and social circumstances (i.e., does the patient have a partner they wish to cryopreserve embryos with rather than oocytes alone). In pre-menarchal females, gonadal tissue cryo-preservation is the only available option as the patient is not yet able to ovulate. In both pre- and post-menarchal females with malignancies who have undergone OTC, the decision to re-implant tissue is based on the reported risk of occult malignant cell contamination of the ovary (although very rarely reported to result in relapsed disease) as well as the potential for future ex vivo oocyte maturation (currently considered experimental). Ovarian tissue reimplantation also has the potential to temporarily restore hormone function.

Males

For prepubertal males, testicular tissue cryopreservation (TTC) represents the only FP strategy, as spermatogenesis has not commenced (Fig. 2) [19]. The procedure entails surgical biopsy of testicular tissue, which is then cryopreserved. Potential future applications include auto-transplantation of spermatogonial stem cells/tissue or in vitro maturation of spermatogonia (cells); however, all of these approaches remain experimental in humans [20,21,22,23,24]. To date, no pregnancies have been reported in humans using TTC, although restoration of spermatogenesis and live births have been achieved in animal models [23,24,25,26].

Fig. 2
Fig. 2The alternative text for this image may have been generated using AI.
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For prepubertal males, TTC is presently offered at some institutions on a research protocol basis, while a few centers may offer it routinely. Semen cryopreservation can be quickly completed for most patients and is the standard of care for post-pubertal males. In rare circumstances, TTC in post-pubertal males may be considered.

Post-pubertal fertility preservation

Females

Oocyte Cryopreservation

Post-pubertal females may undergo oocyte cryopreservation, which involves hormonal stimulation to induce the growth of mature follicles. Oocyte retrieval is performed transvaginally under ultrasound guidance, followed by vitrification for storage. When a future pregnancy is desired, thawed oocytes are fertilized with sperm via in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Reported live birth rates per thawed oocyte range from 4% to 25% [27, 28], thus clinicians aim for collecting as many oocytes as feasible. Time is an important consideration. Some patients may need to proceed immediately to treatment and do not have the 2–3 weeks that are required for hormonal stimulation and collection.

Embryo cryopreservation

Embryo cryopreservation involves ovarian stimulation and oocyte retrieval as described above, followed by fertilization using partner or donor sperm. The resulting embryos are then cryopreserved. In future pregnancy attempts, thawed embryos are transferred into the uterus. Live birth rates per thawed embryo are reported between 30% and 50% [28, 29]. This option is typically not feasible for pediatric/adolescent patients due to their age and relationship status. Similar to oocyte cryopreservation, time is a consideration. For patients who do not have time for oocyte or embryo cryopreservation, ovarian tissue cryopreservation can sometimes be quicker achieved.

Ovarian tissue cryopreservation

In post-pubertal females, OTC follows the same procedure as in prepubertal girls, and can be undertaken rapidly if the patient is safe for anesthesia and surgery. OTC is indicated for patients who are unable to undergo ovarian stimulation or require urgent initiation of gonadotoxic therapy and before highly gonadotoxic treatments. Several hundred live births have been reported (and likely many more not published), and ~30% who have ovarian tissue reimplanted give birth [30,31,32,33,34].

Gonadotropin-releasing hormone agonists (GnRHa)

Gonadotropin-releasing hormone agonists are administered before and during chemotherapy with the aim of suppressing ovarian function and thereby reducing chemotherapy-induced damage [35].

However, evidence regarding their efficacy for FP is debated [36]. The last guidelines of ASCO underlined that GnRHa should not be used in place of established FP methods [37].

Males

Semen Cryopreservation

In post-pubertal males, semen cryopreservation should be done before treatment, even when needing to start therapy emergently. Semen parameters of patients undergoing treatment may be inferior to those of healthy controls due to their underlying condition [38]. At times, cryopreserving multiple samples may be beneficial, if feasible. If there are no sperm in the ejaculate, it may still be possible to retrieve sperm directly from the testes by testicular sperm extraction (TESE) [39, 40].

Treatment-related toxicity and fertility impact

Conditioning regimens administered before HSCT are intrinsically gonadotoxic, leading to profound long-term reproductive endocrine sequelae [41, 42]. These effects are highly dependent on the type and dose of conditioning, and the patient’s age and sex [6, 43]. Understanding the differential impact on gonadal function in males and females is critical for developing FP strategies and optimizing survivorship care; inherent challenges in understanding fertility risk make this task [37].

Females

In females, gonadal impairment manifests along a spectrum ranging from the subclinical “diminished ovarian reserve” (DOR) to overt premature ovarian insufficiency (POI). DOR, characterized biochemically by low anti-Müllerian hormone (AMH) levels and reduced antral follicle count, retains menstrual cyclicity but indicates a diminished follicular pool with compromised fertility potential. In the setting of POI, the combination of amenorrhea, hypoestrogenism and elevated gonadotropins implies extensive follicular depletion, leading to severe endocrine dysfunction along with profound fertility impairment [44, 45].

Overall, the reported incidence of POI following HSCT in childhood ranges from 44 to 100% [43, 46,47,48,49]. This variability reflects differences in the gonadotoxicity of conditioning regimens and demographic diversity. Research into fertility potential is complicated by the long follow-up periods required, as well as a lack of data on patients’ desires for biological parenthood (Table 2). Most studies report pregnancy rates without distinguishing between those who do and do not wish to conceive [50, 51]. While AMH is a useful biomarker in female survivors, it has important limitations [52, 53].

Table 2 Studies of Fertility Potential Among HCT Survivors.
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Both alkylating agents and TBI involve depletion of ovarian reserve in a dose-dependent manner [54]. The gonadotoxicity of conditioning regimens correlates directly with cumulative doses. Biologically, TBI-related gonadotoxicity results from radiation-induced DNA strand breaks, leading to massive follicular apoptosis. Radiation exposure exceeding 10 Gy has been demonstrated to result in POI with occurrence as high as 95–100% among post-pubertal acute myeloid leukemia transplanted survivors [54, 55]. Younger age upon radiation exposure is regarded as protective. Although 40–60% of prepubertal girls <10 years at the time of transplantation experience a progression of puberty and spontaneous menarche, the risk of later-onset POI remains remarkable following TBI. As TBI is never administered as the only treatment, drawing a sterilizing radiant threshold can be cumbersome. Mathematic modeling based on data from rates of oocyte decline has set the following age-dependent thresholds for the risk of developing POI: 20.3 Gy in infants, 18.4 Gy at the age of 10 years, and 16.5 Gy at the age of 20 [56]. However, gonadal doses much lower are associated with a substantial reduction in fertility potential [57, 58].

Among alkylating agents, busulfan is universally acknowledged as the most gonadotoxic, with POI occurrence rates exceeding 90% following standard-dose administration [59, 60]. On the other hand, a greater percentage of retained ovarian function has been reported following cyclophosphamide- and melphalan-based conditioning regimens [55, 61].

In order to compare the cumulative burden of gonadal toxicity following polychemotherapy protocols and to compare regimens, the cyclophosphamide equivalent dose (CED) method has been developed [62]. By applying dedicated coefficients, CED allows clinicians to estimate the overall alkylating dose administered, expressed as an equivalent dose of cyclophosphamide. The CED was derived from comparisons of hematological toxicity across various alkylating agents, so its application to ovarian function should be interpreted with caution” [63]. However, recent studies have shown even among patients with low-moderate risk of infertility based on cumulative CED alone [57], the vast majority of girls undergoing HSCT had very low or undetectable levels of AMH [64, 65]. Alternatively, in a single-center study of patients with aplastic anemia receiving cyclophosphomide (at lower cumulative doses) as the only alkylating agent, the majority were able to achieve pregnancy [66]. Recently, a growing body of literature has highlighted the gonadal-sparing profile of treosulfan, with lower occurrence of POI and need for pubertal induction among patients conditioned at different ages and baseline pubertal status [67]. A conversion factor for Treosulfan CED has yet to be established.

Males

In males, germ cells are more radio- and chemo-sensitive than Leydig cells, and the prevalence of azoospermia following HSCT exceeds 85 to 90% in cohorts of patients transplanted for hematological malignancies or bone marrow failure utilizing myeloablative conditioning regimens [68]. Conversely, testosterone secretion is generally retained following chemo-only regimens [69] while up to half of cancer survivors experience hypogonadism after TBI [70, 71].

The probability and severity of testicular damage are dose-dependent. Based on mathematical models, the radiant sterilizing dose is generally set between 2 (adults) and 6 Gy (pre-pubertal patients). In terms of the detrimental effect of alkylating agents, spermatogonial cell depletion and subsequent oligo-azoospermia frequently occur for busulfan and for cyclophosphamide doses >7.5–9 g/m2 [72, 73]. More recently, a testicular-sparing profile has been hypothesized among patients conditioned with treosulfan [69, 74].

In male survivors, biomarkers beyond formal semen analysis are of limited reliability [75].

Access and cost coverage

FP is now recognized as an essential part of care for pediatric patients undergoing HSCT or other cellular therapies. Despite increasing awareness, access, and implementation remain highly variable across centers.

Differences stem from national legislation, insurance coverage, institutional resources, technical capacity, and awareness among providers and families. Some countries, such as France and Israel, have legally mandated access to FP, whereas others rely on institutional or regional guidelines, leading to significant disparities (Fig. 3).

Fig. 3
Fig. 3The alternative text for this image may have been generated using AI.
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Insurance coverage for various FP procedures varies by state in the United States and by country in Europe. In the United States, individual state laws mandate different degrees of insurance coverage for FP procedures, and significant variability exists between what is and is not covered. Additionally, most states do not mandate individual insurance coverage, and therefore some patients will not have any insurance coverage regardless of state insurance laws. *Coverage for FP procedures but not storage. **Coverage for pre-pubertal ovarian tissue cryopreservation, but not for testicular tissue cryopreservation.

Networks like FertiPROTEKT, the Danish Network, the Oncofertility Consortium (www.oncofertility.northwestern.edu), Alliance for Fertility Preservation (www.allianceforfertilitypreservation.org), Orchid-Net, and the French National Institute (www.cancer.fr) promote standardization and knowledge sharing, supported by organizations such as ESHRE and PanCareLIFE [19, 25, 76,77,78]. In the U.S., the Children’s Oncology Group and the American Society for Reproductive Medicine (ASRM) have issued similar guidelines to expand equitable FP access [79,80,81].

Although financial support has improved, major gaps persist—particularly for prepubertal patients and in regions without national coverage. The authors herein advocate for universal access to FP counseling and funding for all pediatric HSCT patients to ensure equity in fertility care.

Implementation and timing of fertility preservation

The timing of FP in children and adolescents referred for HSCT depends on balancing several key factors. Early counseling and referral to reproductive specialists are essential, ideally at diagnosis, when HSCT is a likely therapeutic path. A disease-specific, individualized approach should identify possible “windows of opportunity” at diagnosis, between treatment cycles, in remission, or just before conditioning (Table 3).

Table 3 Considerations on Timing and Feasibility of Fertility Preservation.
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At various time-points in a patient’s treatment, FP should be re-examined and potentially rediscussed. Some patients have an existing, but often shortened, reproductive window after HSCT [82]. If primary FP was not performed, was ineffective, or done in prepubertal patients before gonadotoxic treatment, secondary FP should be considered approximately 1 year after treatment or after entering puberty [83].

Risk of malformation following chemotherapy exposure

Children born via spontaneous conception to fathers who underwent chemotherapy or radiotherapy years prior do not demonstrate a significant increase in the risk of congenital malformations compared to the general population [84, 85]. Patients should be advised of potentially higher genetic damage risks in sperm collected immediately post cancer-directed therapy [37].

Similarly, children of mothers who are cancer survivors and received chemotherapy or radiotherapy prior to conception do not appear to have an increased malformation risk compared to the general population [86].

Risk of malformation after fertility preservation

Data concerning the risk of congenital malformations following FP are scarce, and long-term cohorts of women who conceive after returning vitrified oocytes or frozen-thawed ovarian tissue for cancer are needed. In a large registry cohort of singleton livebirths, children conceived without medical assistance had a 4.2% incidence of major malformation. In the context of assisted reproductive technologies, this risk is 6% after fresh intracytoplasmic sperm injection(ICSI), 5.3% conceived using fresh in vitro fertilization(IVF), and 4.9% of children conceived using cryo-ICSI [87].

Pregnancies from vitrified oocytes demonstrate no significant rise in anomaly rates compared with fresh oocytes, with reported incidences around 1–2% [88]. Although data on offspring from ovarian tissue reimplantation (OTT) after OTC remain limited, especially in those who underwent OTC during childhood, no clear evidence suggests an excess risk compared to spontaneous or ART conceptions [89]. Similarly, sperm cryopreservation, while potentially affecting sperm function or structure, has not been associated with higher congenital anomaly rates [90].

Risk of malignant cell reintroduction

Reimplantation of cryopreserved gonadal tissue carries a potential risk of malignant cell reintroduction, particularly in diseases with bone marrow involvement. Collecting tissue during complete remission reduces this risk, though the optimal threshold—based on bone marrow morphology, flow cytometry, or next-generation sequencing—remains undefined [91,92,93]. Minimal residual disease has been detected in both ovarian and testicular tissue from leukemia patients [92,93,94].

Despite these concerns, several successful OTT after leukemia have been reported, with only one relapse reported [95,96,97,98,99,100]. Harvesting post-chemotherapy tissue may further lower contamination risk [101]. Laboratory decontamination protocols and in vitro procedures from cryopreserved tissue are emerging research strategies to restore fertility while avoiding reimplantation of malignant cells [102, 103].

Special considerations

Gene therapy

Emerging treatments using genetically modified hematopoietic stem cells show encouraging outcomes for non-malignant disorders such as leukodystrophies, immunodeficiencies, and hemoglobinopathies. Current protocols typically include myeloablative conditioning with alkylating agents. Fertility counseling before therapy should include discussion of the risk of inherited transmission of the underlying genetic disease, discuss available preservation options and timing, and consider specific factors such as anesthesia safety, iron overload, and discontinuation of hydroxyurea [104].

Chimeric antigen receptor T cell therapy

Assessing fertility risk from CAR T-cell therapy alone is difficult, as most patients also receive gonadotoxic agents like cyclophosphamide for lymphodepletion. Despite this, live births have occurred following CAR T-cell therapy [105]. Potential fertility effects may arise from inflammatory or immune-mediated mechanisms [106]. Theoretical risks include transplacental passage of CAR T-cells, possibly affecting fetal B-cell function [105, 107].

Uterine dysfunction following TBI or busulfan exposure

Along with gonadal insufficiency, uterine function can be affected following HSCT. Irradiation may damage the uterus and compromise fertility irrespective of ovarian insufficiency. In addition, patients who conceive following TBI show remarkably greater rates of pregnancy and birth complications, including abortion, preterm delivery and low-birth weight [108, 109]. Abnormal uterine function following TBI is an integrated effect of prolonged hypoestrogenism plus direct radiation-induced changes [110]. The latter includes impaired uterine vascularization, iatrogenic loss of elasticity and negative effect on endometrial health and embryo receptivity [111, 112]. Younger age upon exposure results in smaller uterine volumes in adulthood, supporting the hypothesis of the detrimental role of TBI on early organ development [113].

Although TBI has been identified as most damaging, uterine volume may also be negatively affected by alkylating agents. A case-control study involving 88 transplanted patients from 13 French Centers showed alkylating agents- and TBI-based conditioning regimens were associated with a 43% and 75% reduction of uterine volume compared to healthy women, respectively, despite adequate hormonal replacement therapy [114].

Accordingly, pregnant women who have undergone HSCT deserve dedicated pre-conceptional counselling and close gynecological follow-up, in case of complications arising over gestation. A study recently compared the pregnancy outcomes of 86 women who conceived following HSCT for pediatric ALL versus 180 patients exposed to conventional chemotherapy [115]. Despite superimposable outcomes between alkylating-based conditioning regimens and conventional chemotherapy, TBI was associated with higher occurrence rates of miscarriage (24% versus 3%), preterm delivery (50% verses 5%), intrauterine growth restriction (21% versus 5%), and postpartum hemorrhage (31% versus 10%).

Gonadal insufficiency risks post-fertility preservation

Results are conflicting, and long-term data about ovarian reserve following OTC are lacking. In a study published by the French L.E.A network on ovarian function outcomes among patients treated with HSCT before puberty, unilateral oophorectomy for OTC was associated with an increased risk of POI [116]. However, these conclusions are drawn from a limited sub-cohort of only 13 patients. In addition, there was a statistically significant association between exposure to OTC and older age at HSCT, a universally acknowledged independent risk factor for ovarian damage. Khan et al. suggested a compensatory mechanism involving the contralateral ovary, as women with a single ovary who underwent IVF show a higher number of oocytes retrieved as compared to the ipsilateral ovary in women with bilateral ovaries [117]. Assessing the burden of unilateral oophorectomy on the timing of menopause onset is hampered by conflicting published outcomes. While epidemiological models estimate that unilateral oophorectomy anticipates the onset of menopause only by one year [118, 119], Teinturier and colleagues demonstrated a 7-year anticipation among cancer survivors [120].

In contrast, hemi-oophorectomy or cortical biopsies preserve more ovarian tissue in situ, but the remaining cortex could be exposed to the surgery-related damage and to gonadotoxic treatments. Plus, the overall amount of cortical tissue available for future reimplantation is reduced compared to whole-ovary withdrawal.

Fertility preservation in countries with growing transplant activity but limited prior FP experience

Hematopoietic cell transplantation, particularly with PTCy-based approaches, is expanding in regions such as the Middle East, Africa, and Southeast Asia. Despite this growth, access to fertility preservation (FP) services in many of these areas remains limited. Establishing partnerships with countries that have established FP programs would help ensure that patients in these regions can benefit from appropriate FP options.

Conclusion

FP has become an integral component of comprehensive care for children and adolescents undergoing HSCT. Advances in cryopreservation, surgical techniques, and multidisciplinary counseling have significantly improved the prospects for reproductive health among survivors. However, access, timing, and implementation remain inconsistent across institutions and countries, reflecting variations in resources, legislation, and awareness.

To achieve equitable care, standardized international guidelines, structured referral pathways, and financial coverage must be universally adopted. Continued collaboration among transplant physicians, FP specialists, and policymakers will be essential to ensure that every pediatric patient facing HSCT is offered timely counseling and the opportunity for FP, regardless of geographic or socioeconomic barriers.