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Polycythemia Vera in Pregnancy: What Patients and Clinicians Should Know

Feb 9, 2026

Key takeaways

  • Polycythemia vera (PV) in pregnancy is rare but often manageable with expert care. [1][2]
  • Key risks include blood clots, miscarriage, and placental blood-flow problems related to increased blood cell counts and pregnancy-associated clotting changes [1][2][3]
  • Close monitoring, low-dose aspirin, and—when cytoreduction is needed—interferon therapy can improve pregnancy outcomes. [1][2][3]

Overview

Pregnancy in women with polycythemia vera (PV) is uncommon, but when it occurs, it requires close medical supervision. PV increases the number of red blood cells, which can raise blood viscosity and thrombotic risk. During pregnancy, these changes may interfere with blood flow through the placenta (the organ that supplies oxygen and nutrients to the baby) and increase the risk of complications such as miscarriage, pre-eclampsia (high blood pressure and protein in the urine), fetal growth restriction, and blood clots. [1][2][3]


Although the risks are real, successful pregnancies are still possible. Published cohorts and reviews suggest that outcomes have improved with structured management—often including low-dose aspirin, control of hematocrit (e.g., with phlebotomy and/or interferon when indicated), and multidisciplinary monitoring. [1][2][3]


Because pregnancy itself increases clotting tendency, a personalized plan developed by a hematologist and a high-risk obstetrician is essential. This partnership helps balance maternal health and fetal safety, including decisions on antithrombotic prophylaxis, timing of delivery, and postpartum care. [1][2][4]

Why PV poses special challenges in pregnancy

During pregnancy, blood volume naturally increases. In women with PV, increased blood cell production can still contribute to hyperviscosity and placental circulation problems, which may affect oxygen and nutrient delivery [1][2]


This can increase the risks of:


  • Miscarriage or stillbirth
  • Pre-eclampsia
  • Fetal growth restriction
  • Blood clots in the mother (deep vein thrombosis or pulmonary embolism) [1][3]

Common complications and their frequency

Outcomes have improved, but PV pregnancies still show higher complication rates than the general population in published cohorts:

  • Pregnancy loss: Earlier series and reviews report elevated first-trimester loss rates in PV, with risk varying across studies and generally improving with modern antithrombotic and hematocrit-focused management. [1][3][5]
  • Preterm birth: Reported preterm birth rates vary across cohorts and may occur due to fetal growth concerns or maternal complications. [2][3][6]
  • Thrombosis (clots): Thrombotic events can occur during pregnancy and are a particular concern postpartum, supporting a prevention plan tailored to individual risk factors. [1][2][4]

Management during pregnancy

Pregnancy in polycythemia vera (PV) is typically managed with an individualized, specialist plan under coordinated obstetric–hematology care. The focus is maternal safety (including reducing clot risk), maintaining blood counts in an appropriate range when needed, and monitoring fetal growth with ultrasound (with additional placental assessment when clinically indicated). [1][3]

Delivery and postpartum care

Because pregnancy can change benefit–risk considerations, the care team will usually review current medications early, since some PV therapies are generally avoided in pregnancy, and treatment choices may differ during pregnancy and after delivery.

Delivery and postpartum care are likewise individualized, often including a tailored plan for clot-prevention and follow-up after birth, and—if breastfeeding is relevant—reviewing medication compatibility using established lactation references. [1]


Long-term outcomes

Most women with PV who receive coordinated modern care have successful pregnancies. Across MPN pregnancy literature, better outcomes are reported when maternal thrombosis risk is addressed and disease control is optimized. [1][2][3]


Good control of hematocrit and close medical supervision are consistent predictors of better outcomes across reports and guidance. [1][2][3]

Final thoughts

Pregnancy in women with polycythemia vera is uncommon but often achievable with careful planning. Where possible, planning ahead with your specialist team, ongoing monitoring throughout pregnancy, and an individualized approach to reducing clot risk and keeping blood counts in a safe range are central to many care plans, along with a clear postpartum follow-up and prevention strategy. [1][2][3]

Frequently asked questions (FAQs)

1. Can women with PV have a safe pregnancy?

Many women can, but PV increases risks. Outcomes are generally better with coordinated hematology–maternal-fetal medicine care and an individualized prevention plan. [1][2]


2. How does PV affect the baby?

Placental blood-flow problems can contribute to fetal growth restriction and other complications, which is why ultrasound surveillance is often used. [1][2]


3. Is breastfeeding safe while on PV treatment?

Breastfeeding is generally compatible with LMWH and low-dose aspirin, and considered permissible with interferon in major guidance and lactation references; confirm your regimen with your clinicians. [1][7][8]


4. Should women with PV plan their pregnancies differently?

Yes. A preconception visit (or early pregnancy consultation) helps review medications, optimize disease control, and plan thrombosis prevention through pregnancy and the postpartum period. [1][2]

Abbreviation

PV — Polycythemia vera

MPN — Myeloproliferative neoplasm

MPNs — Myeloproliferative neoplasms

LMWH — Low-molecular-weight heparin

FAQs — Frequently asked question

References

  1. McMullin, M. F. F., Mead, A. J., Ali, S., Cargo, C., Chen, F., Ewing, J., Garg, M., Godfrey, A., Knapper, S., McLornan, D. P., Nangalia, J., Sekhar, M., Wadelin, F., & Harrison, C. N. (2019). A guideline for the management of specific situations in polycythaemia vera and secondary erythrocytosis: A British Society for Haematology Guideline. British Journal of Haematology, 184(2), 161–175. https://doi.org/10.1111/bjh.15647
  2. Robinson, S., Ragheb, M., & Harrison, C. (2024). How I treat myeloproliferative neoplasms in pregnancy. Blood, 143(9), 777–785. https://doi.org/10.1182/blood.2023020729
  3. Maze, D., Kazi, S., Gupta, V., Malinowski, A. K., Fazelzad, R., Shah, P. S., & Shehata, N. (2019). Association of treatments for myeloproliferative neoplasms during pregnancy with birth rates and maternal outcomes: A systematic review and meta-analysis. JAMA Network Open, 2(10), e1912666. https://doi.org/10.1001/jamanetworkopen.2019.12666
  4. Wille, K., Wille, K., Sadjadian, P., & Griesshammer, M. (2021). The management, outcome, and postpartum disease course of 41 pregnancies in 20 women with polycythemia vera. European Journal of Haematology, 107(1), 122–128. https://doi.org/10.1111/ejh.13627
  5. European LeukemiaNet. (n.d.). Project 9: Pregnancy in Chronic myeloproliferative diseases (CMPD). https://www.leukemia-net.org/leukemias/mpn/pregnancy/
  6. Ravn Landtblom, A., Andersson, T. M.-L., Johansson, A. L. V., Brismar Wendel, S., Lundberg, F. E., Samuelsson, J., Björkholm, M., & Hultcrantz, M. (2022). Pregnancy and childbirth outcomes in women with myeloproliferative neoplasms—a nationwide population-based study of 342 pregnancies in Sweden. Leukemia, 36, 2461–2467. https://doi.org/10.1038/s41375-022-01688-w
  7. Drugs and Lactation Database (LactMed). (2025, August 15). Interferon alfa. In Drugs and Lactation Database (LactMed). National Library of Medicine (US). https://www.ncbi.nlm.nih.gov/books/NBK500992/
  8. Drugs and Lactation Database (LactMed). (2025, August 15). Peginterferon alfa. In Drugs and Lactation Database (LactMed). National Library of Medicine (US). https://www.ncbi.nlm.nih.gov/books/NBK500646/