-Original-

Pregnancy Transiently Normalized Platelet Counts in Essential Thrombocytosis

Shunsuke Homma^*, Satoshi Wakita^*, Masahiro Sakaguchi, Shunsuke Yui, Koiti Inokuchi and Hiroki Yamaguchi

Department of Hematology, Nippon Medical School, Tokyo, Japan
^*Contributed equally

Background: Outcomes of pregnancies complicated by essential thrombocytosis (ET) are worse than those of normal pregnancies. Aspirin, heparin, and interferon (IFN)-α are well-tolerated during pregnancy and prescribed in accordance with the risk of thrombosis. However, some evidence suggests that platelet count decreases during ET-complicated pregnancies.
Methods: We retrospectively analyzed changes in platelet count in ET-complicated pregnancies.
Results: Platelet count decreased during pregnancy without IFN-α use, and 83% of pregnant women had a platelet count of ≤450×10⁹/L. Furthermore, all pregnant women achieved a platelet count of ≤600×10⁹/L. One the basis of revised IPSET-thrombosis score, risk was classified as low or very low. Aspirin use starting in early pregnancy was associated with a higher rate of successful delivery, even in patients with prior miscarriage.
Conclusions: These findings suggest that platelet counts decrease in selected low-risk and very-low-risk ET-complicated pregnancies and that cytoreductive therapy with IFN-α may be avoidable in some cases. These results should be interpreted cautiously because of the small sample size and retrospective study design.

J Nippon Med Sch 2026; 93: 323-332

Keywords
essential thrombocytosis, platelet, pregnancy, interferon α, aspirin

Correspondence to
Satoshi Wakita
aaa11140@nms.ac.jp

Received, May 1, 2026
Accepted, May 18, 2026