Conditioning Intensity and Probability of Live Birth after Blood or Marrow Transplantation (BMT) - a Report from the BMT Survivor Study (BMTSS)

Background: The observed inter-individual variability in the probability of live birth after BMT is due to exposure to gonadotoxic agents (including total body irradiation [TBI]), age at exposure to gonadotoxic agents, sex of the BMT recipient, and post-BMT morbidity. The last decade has seen an increase in use of non-myeloablative (NMA) conditioning to reduce the risk of early post-treatment mortality. However, the impact of TBI in the context of conditioning intensity (NMA vs. myeloablative conditioning [MAC]) on the probability of post-BMT live birth remains unknown. We addressed this gap by utilizing the BMTSS - a multi-institutional collaborative designed to understand the burden of morbidity after BMT.

Methods: This study included 1,607 BMT survivors who underwent BMT between 1974 and 2014 at age ≤45, had survived ≥2y, and were ≥18y of age at study. This study also included pair-matched nearest-age, same-sex biologic siblings (≥18y of age at study) to control for genetic or environmental factors that could affect fertility. Survivors and their siblings completed the BMTSS survey. Sociodemographic characteristics (race/ethnicity, annual household income, availability of health insurance, level of education), chronic health conditions, medical assistance for fertility assistance and details about all pregnancies and their outcomes were retrieved from the BMTSS survey. Clinical characteristics were obtained from the institutional BMT databases and/or participants' medical record. Within survivor analysis: Potential risk factors for not reporting a live birth after BMT were analyzed using multivariable logistic regression. Exposure to TBI and conditioning intensity were consolidated to create four distinct exposure groups: no_TBI/NMA (least intense), TBI/NMA, no_TBI/MAC, TBI/MAC (most intense). Matched-pair comparison with biologic siblings: We matched 172 survivors with their closest-age, same-sex, biological siblings and used conditional logistic regression to determine the failure to report live birth in BMT survivors when compared with their siblings.

Results: In this cohort of 1,607 survivors, 599 (37.3%) were autologous BMT recipients, and 765 (47.6%) were female. Median age at BMT was 30y, and at study participation was 45y (IQR: 18-73); median length of follow-up from BMT to study was 14.4y (IQR: 2.4-41.4). The primary indications for BMT included HL/NHL (30.6%), AML/MDS (24.3%), CML (13.4%), ALL (12.2%), and other diagnoses (13.5%). Of the 1,607 survivors, 120 (7.5%) reported one or more live births after BMT. Within survivor comparison: Multivariable analysis (Figure) revealed that receipt of TBI/MAC (OR=2.9, 95%CI: 1.5-5.8; ref: no_TBI/ NMA) was associated with an increased risk of not reporting a post-BMT live birth. Of note, TBI/NMA (OR=1.5, 95%CI, 0.5-5.0), and no_TBI/ MAC (OR=0.9, 95%CI, 0.4-2.0) were at a similar risk of reporting a post-BMT live birth as no_TBI/NMA. Other factors associated with increased risk of not reporting a post-BMT live birth included older age at BMT (>35y: OR=3.5, 95%CI, 1.4-7.9; reference: <12y), lower income ($50k-100k: OR=2.0, 95%CI, 1.1-3.6; <$50k: OR=3.2, 95%CI, 1.6-6.4; reference: >$100k), no medical interventions to facilitate pregnancy (OR=2.7, 95%CI, 1.6-4.6), and history of pre-BMT live birth (OR=2.7, 95%CI, 1.6-4.6). Matched-pair comparison with biologic siblings: Multivariable conditional logistic regression revealed that BMT survivors were less likely to report live birth (OR=0.5, 95%CI: 0.3-0.8) compared to their siblings. However, once pregnant, they were also less likely to report a miscarriage (OR=0.4. 95%CI: 0.2-0.8).

Conclusion: While full dose TBI in the setting of myeloablative conditioning is associated with a lower probability of live birth after BMT, lower doses of TBI in the setting of myeloablative or reduced intensity conditioning yield a similar probability of live birth as no TBI. These findings provide evidence for alternative conditioning regimens for patients who wish to have children after BMT.

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