Management of myeloproliferative neoplasms in pregnancy: Essential thrombocythemia, polycythemia vera, and primary myelofibrosis.

Pregnancy in patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) is uncommon but clinically challenging. Essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF) are clonal hematopoietic stem cell disorders characterized by myeloid proliferation, JAK-STAT pathway activation, and an increased risk of thrombotic and hemorrhagic complications. Pregnancy itself is a hypercoagulable state, and when it occurs in patients with MPNs, maternal and fetal complications are more frequent than in the general population. The most common fetal complications are first trimester pregnancy loss, placental insufficiency, fetal growth restriction, preeclampsia, preterm delivery, and stillbirth. Maternal complications include venous and arterial thrombosis, bleeding, acquired von Willebrand syndrome, and postpartum thromboembolism. ET is the most frequently encountered MPN in pregnancy and generally carries the most favorable prognosis. PV is associated with higher thrombotic and placental risk, largely related to erythrocytosis and hyperviscosity. Pregnancy in PMF is rare, and available data are limited to small series and case reports, making management particularly dependent on expert opinion. The mainstay of treatment is risk-adapted therapy with low-dose aspirin, low-molecular-weight heparin, phlebotomy for PV, and interferon-based cytoreduction when needed. Hydroxyurea, anagrelide, and JAK inhibitors are generally avoided due to limited fetal safety data. Given the paucity of prospective evidence, management should be individualized and coordinated by hematology and maternal-fetal medicine specialists. This review summarizes current data on MPN pregnancy outcomes and provides a practical approach to preconception counseling, antepartum management, delivery planning, postpartum care, and future research priorities.