Pregnancy With Blood Cancer Precursor Carries Fivefold Higher Death Risk, Large Database Study Finds

Pregnant women living with a group of rare bone marrow disorders called BCR::ABL1-negative myeloproliferative neoplasms face dramatically higher risks during pregnancy than previously appreciated, including a more than fivefold increase in all-cause mortality, according to one of the largest real-world analyses ever conducted on this overlooked patient population. The study, drawn from an enormous multi-institutional medical records database, compared thousands of pregnancies complicated by these blood cancers against carefully matched healthy pregnancies and found consistent excess risk across nearly every major maternal and obstetric outcome measured.

Myeloproliferative neoplasms, or MPNs, are chronic blood cancers in which the bone marrow produces too many of one or more types of blood cells. The most common subtype, essential thrombocytosis, drives an overproduction of platelets, while related conditions such as polycythemia vera and primary myelofibrosis cause excess red blood cells or marrow scarring. Because these diseases typically emerge in middle age, they are uncommon in women of reproductive age, yet they are increasingly diagnosed in younger patients and often first surface during routine pregnancy bloodwork. That timing matters enormously, because pregnancy itself transforms the hemostatic system into a pro-coagulant state, amplifying the very thrombotic tendencies that define MPN biology.

The new research, led by a multicenter team of hematologists and internal medicine physicians and published in Annals of Hematology, exploited the TriNetX database, a federated network of electronic health records spanning millions of patients treated across major healthcare organizations. The investigators searched through 4,467,127 recorded pregnancies and identified 4,563 patients in whom an MPN diagnosis coincided with pregnancy. The overwhelming majority, roughly 85 percent, had essential thrombocytosis, a distribution that mirrors the general epidemiology of MPNs in younger women and underscores why platelet-driven vascular risk dominates the clinical picture in this setting.

A central strength of the analysis lies in its methodological design. Rather than simply comparing MPN pregnancies to the general obstetric population, the researchers used propensity score matching, a statistical technique that pairs each MPN patient with control pregnancies sharing similar baseline characteristics, including age, comorbidities, and antithrombotic medication use. After matching, standardized mean differences for all covariates fell below 0.1, the conventional threshold indicating that the two groups were statistically well balanced. This approach substantially reduces confounding, meaning that the excess risks observed can be attributed with far greater confidence to the MPN itself rather than to demographic or clinical differences between the groups.

The results were striking. Pregnant patients with MPNs died during the study period at a rate of 1.1 percent, compared with just 0.2 percent among matched controls, yielding a hazard ratio of 5.4 with a 95 percent confidence interval of 2.7 to 10.8. While absolute mortality remained low, the magnitude of the relative elevation is sobering in an obstetric population where death is otherwise exceedingly rare. The researchers caution that mortality in such database studies can reflect deaths recorded around the pregnancy window and that the underlying causes, whether thrombotic, hemorrhagic, or disease-progression related, warrant closer investigation in future work.

Hypertensive complications of pregnancy emerged as another major signal. Gestational hypertension affected 11.1 percent of MPN pregnancies versus 7.8 percent of controls, a hazard ratio of 1.3. More severe disease followed the same pattern: preeclampsia and eclampsia occurred in 10.4 percent of MPN patients compared with 5.3 percent of controls, nearly doubling the risk with a hazard ratio of 1.8. Preeclampsia, a disorder of abnormal placental vascular development characterized by high blood pressure and organ dysfunction, is a leading cause of maternal and fetal morbidity worldwide, and its association with MPNs fits a coherent biological narrative in which dysregulated blood cells, endothelial injury, and impaired placental perfusion reinforce one another.

The pattern of elevated risk extended deep into labor and delivery outcomes. Preterm labor occurred in 6.1 percent of MPN pregnancies against 3.7 percent of controls, translating to a hazard ratio of 1.5. Intrauterine growth restriction, in which the fetus fails to reach its expected size because of inadequate nutrient and oxygen delivery through the placenta, was documented in 7.3 percent versus 5.1 percent of controls, a hazard ratio of 1.3. Postpartum hemorrhage, one of the most feared obstetric emergencies, affected 5.5 percent of MPN patients compared with 3.8 percent of controls, a hazard ratio of 1.3. The hemorrhage finding is particularly notable given that many MPN patients receive antiplatelet or cytoreductive therapy, and it highlights the delicate balancing act clinicians face between preventing clots and avoiding dangerous bleeding.

Venous thromboembolism, the umbrella term for deep vein thrombosis and pulmonary embolism, showed one of the largest risk elevations of any outcome studied. It occurred in 2.7 percent of MPN pregnancies versus 0.7 percent of matched controls, a hazard ratio of 3.2 with a confidence interval of 2.2 to 4.6. Pulmonary embolism in particular remains a leading cause of pregnancy-related death in high-income countries, and a near fivefold relative increase in venous clotting events among a young, otherwise relatively healthy population carries immediate implications for how obstetricians and hematologists collaborate. Interestingly, arterial thrombotic events were not significantly different between the two groups after matching, suggesting that in the pregnancy setting the venous circulation may bear the disproportionate burden of MPN-related clotting risk, a nuance that could shape future prophylaxis strategies.

The authors argue that these findings make a compelling case for multidisciplinary management, bringing hematologists, maternal-fetal medicine specialists, and anesthesiologists together early in every MPN pregnancy. They emphasize individualized thromboprophylaxis, meaning that decisions about low-molecular-weight heparin, low-dose aspirin, or cytoreductive agents such as interferon should be tailored to each patient’s mutation profile, platelet count, prior thrombotic history, and obstetric risk factors rather than applied uniformly. For essential thrombocytosis patients harboring the JAK2 or CALR mutations, for example, risk stratification algorithms already inform treatment in the non-pregnant setting, and the new data suggest those frameworks should be integrated into prenatal care pathways from the first trimester onward.

As with all retrospective database studies, certain limitations temper the conclusions. Coding accuracy for rare diagnoses and outcomes can vary across institutions, residual confounding from unmeasured variables such as smoking, body mass index, or disease duration cannot be excluded, and the TriNetX population may not generalize to all healthcare systems globally. Still, the sheer scale of the cohort, with more than four thousand matched MPN pregnancies, dwarfs most prior evidence, which has largely consisted of single-center case series and registry reports numbering in the dozens or hundreds. By anchoring the risk estimates in a propensity-matched design, the study provides the clearest quantitative picture to date of what an MPN diagnosis means for a pregnancy, and it is likely to influence clinical guidelines, counseling conversations, and future prospective research into how these chronic blood cancers can be managed safely through one of medicine’s most physiologically demanding journeys.

Subject of Research: Obstetric and thrombotic outcomes in pregnant patients with myeloproliferative neoplasms

Article Title: Obstetric and thrombotic outcomes among pregnant patients with myeloproliferative neoplasms: a propensity score matched real-world analysis

Article References: Vojjala, N., Srungavarapu, S. R., Nanjareddy, S., Kannan, M. V., Prabhu, R., Arsene, C., Krishnamoorthy, G., & Singh, V. (2026). Obstetric and thrombotic outcomes among pregnant patients with myeloproliferative neoplasms: a propensity score matched real-world analysis. Annals of Hematology. https://doi.org/10.1007/s00277-026-07285-6

Image Credits: AI Generated

DOI: 10.1007/s00277-026-07285-6

Keywords: myeloproliferative neoplasms, essential thrombocytosis, pregnancy outcomes, venous thromboembolism, preeclampsia, propensity score matching, TriNetX, postpartum hemorrhage, maternal mortality, thromboprophylaxis, Obstetric, thrombotic