A Systematic Review and Meta-Analysis
We performed a systematic review and meta-analysis to evaluate the risk of venous thromboembolism (VTE) in pregnant women with essential thrombocythemia (ET). Twenty-one trials with 504 patients and 756 pregnancies met our inclusion criteria. Among 756 pregnancies, the antepartum VTE risk was 1.3% (95% CI, 0.6-2.2) in all pregnancies. Of the 18 studies that reported VTE outcomes and antepartum LMWH use, there were 8 antepartum VTE events among 407 pregnancies without LMWH use (2.5%, 95% CI, 1.3-4.3). Among all 575 pregnancies with postpartum follow-up (excluding first trimester losses), the postpartum VTE risk was 1.8% (95% CI, 0.7-3.4). Of the 14 studies that reported VTE outcomes and postpartum LMWH use, there were 6 postpartum VTE events among 229 pregnancies without LMWH use (4.4%, 95% CI, 1.2-9.5). The absolute risk of VTE in the postpartum period is above a threshold where postpartum LMWH prophylaxis should be considered. The absolute risk of VTE in the antepartum period is not above a threshold where antepartum LMWH is clearly indicated or below a threshold where LMWH should be withheld, hence a preferences and values-based discussion is important when counseling women with ET in pregnancy.