Abstract: Maternal and fetal outcomes of pregnancy in essential thrombocythemia: A systematic review.

Abstract Introduction Approximately 20% of women with essential thrombocythemia (ET) are below the age of 40 with childbearing potential. However, there remains vital knowledge gaps in the current literature on ET in pregnancy, hindering optimal clinical decision-making. The absence of risk stratification models applicable in the context of pregnancy leads to much of the management protocols being based on the non-pregnant population and expert opinions rather than robust evidence. As novel therapeutics emerge, given the exclusion of pregnant individuals from clinical trials, other forms of research need to be concurrently conducted to evaluate their benefits in the pregnant population. As such this systematic review aims to investigate the efficacy of current therapeutic interventions for ET in pregnancy with the aim of improving maternal and fetal outcomes as well as identifying areas requiring further research. Methods A systematic review was conducted in line with the PRISMA 2020 guidelines, including results from PubMed, EMBASE, Scopus and Web of Science from January 2000 – April 2025. Key terms such as “Essential Thrombocythemia,” “Pregnancy,” and “Management” were utilised. Eligible studies were retrospective cohort studies and case reports of pregnant women with ET receiving aspirin (ASA), interferon (IFN), low-molecular weight heparin (LMWH), or no treatment. Studies that did not include unique new cases or were non-peer-reviewed or expert opinions were excluded. Study quality was assessed by 2 independent reviewers using JBI Critical Appraisal tools. Data synthesis was primarily narrative due to anticipated heterogeneity. Outcomes The search identified 493 studies of which 28 studies met the inclusion criteria. A common reason for exclusion was lack of data regarding patient intervention and lack of unique additional cases reported. Included studies reported on 1298 pregnancies: median age 30.25 years (16-45), median platelet levels 833 (414-1990/10^9/L), patients above 35 years-of-age 25.72% (n=98, 18 studies), history of miscarriage 23.7% (n=62, 13 studies), history of thrombosis/haemorrhage 5.49% (n=44, 21 studies). In terms of interventions, combination therapy gave rise to the highest live birth rates (LBR): ASA+LMWH (81.71% LBR, 67 pregnancies, 4 studies), ASA+IFN (90% LBR, 18 pregnancies, 8 studies). Meanwhile, monotherapies of ASA, IFN and LMWH had a LBR of 75% (224 pregnancies, 13 studies), 82.5% (103 pregnancies, 10 studies) and 83.9% (56 pregnancies, 5 studies) respectively. Patients who did not undergo any antiplatelet or cytoreductive therapy had a LBR of 41.2% (97 pregnancies, 6 studies). These results highlight the pertinence of appropriate therapeutics in significantly decreasing adverse obstetric outcomes. While the data is encouraging, it is notable that there were limited studies evaluating the efficacy of ET management in pregnancy and there were no studies which investigated the lived experiences of patients, limiting patient-centred outcomes. The limited applicability of the data is compounded by the lack of diversity in study origin, with 67.9% of them being based on European populations (Italy contributing to the largest share 32.1%). The skewed distribution implies that the racial and genetic profile of major world populations may not be accounted for in existing literature. The distribution also indicates that the data sources are more reflective of well-resourced settings with more advanced healthcare hence limiting the applicability of these results internationally. Lastly, analysing the diversity of publications revealed that around 62% came from haematological journals and 33.3% from obstetric journals indicating potential opportunities for improved cross disciplinary research and collaboration. Conclusion Existing therapeutics show promise in improving patient outcomes, with combination therapy being most beneficial, but there remain considerable gaps in our understanding concerning risk-stratification of patients and optimal treatment protocols. Patient lived experience and population diversity are areas that should be tackled in future research. This would improve patient-cantered outcomes as well as aid in investigation of population-specific risk factors and the socio-economic factors influencing pregnancy outcomes in ET. The complexity of ET in pregnancy and pregnancy planning, necessitates comprehensive, collaborative cross-disciplinary care and research.