How do you manage a patient with JAK2+ ET without history of thrombosis during pregnancy?

Great question. We've recently published our experience here How et al., PMID 33022566. Patients with ET that are pregnant and that don't have a history of thrombosis are likely to be in the very low/low risk categories by R-IPSET, many of these women are likely not on any treatment prior to starting their pregnancy and pregnancy should not change that. My only recommendation is to add a baby aspirin as this does seem to improve pregnancy outcomes. In addition, I usually recommend 6 weeks of post-partum enoxaparin. It's interesting to observe blood counts change in pregnancy and sometimes platelets will even normalize as an expected pregnancy phenomenon. The key for these low risk patients is not to over-treat them. If cytoreduction is needed for some reason interferon is the preferred agent, but I would not start that pre-emptively. 

I agree with what Dr. @Dr. First Last said. When a patient starts trying to get pregnant, I make sure to stop hydroxyurea, ruxolitinib, etc. If they require cytoreduction, (i.e., PV or high risk ET), I start pegylated interferon (Pegasys), at this point, I don't believe there is enough data available for the use of ropeginterferon. I start patients on a baby aspirin, and consider post-partum treatment. I do not pre-emptively treat patients with lower risk ET with interferon, however. I also recommend they get a high risk OB to help manage the pregnancy.