Aspirin therapy is associated with a lower risk of pregnancy loss in both JAK2‐ and CALR‐mutated essential thrombocythemia—A Mayo Clinic study of 200 pregnancies

Two‐hundred pregnancies involving 100 women with essential thrombocythemia (ET) were accessed from Mayo Clinic databases (1990–2023). Median platelet count displayed a decline during pregnancy, nadiring at 48% of baseline, in the third trimester: 704–369 × 109/L. Live birth rate was 72%. Of 53 (27%) unintentional pregnancy losses, 48 (24%) occurred in the first trimester. Other fetal complications included preterm birth 3%, intrauterine growth retardation 3%, and stillbirth 1%. Maternal complications included major hemorrhage (7%), preeclampsia (6%), thrombosis (1%), and placental abruption (0.5%). Antepartum management included no specific therapy in 52 (26%), aspirin alone in 112 (56%), aspirin combined with cytoreductive drugs or systemic anticoagulants in 23 (12%), and other permutations in the remaining. Postpartum systemic anticoagulation was documented in 29 (15%) pregnancies. Unintentional first‐trimester loss was predicted by prior fetal loss (43% vs. 18%; p