Incidence of first immune thrombocytopenia (ITP) worsening during pregnancy among matched pregnant and nonpregnant women with ITP. First ITP worsening was evaluated by a composite end point, including first event of severe thrombocytopenia <30 × 10⁹/L and/or bleeding event and/or treatment modification/initiation. First event and multiple events were assessed. (A) ITP worsening-free probability (and 95% confidence interval [CI]) was estimated with the Kaplan-Meier method and compared in the 2 groups with the use of a Cox model with shared frailty. (B-D) Free probability of severe thrombocytopenia (platelet count <30 × 10⁹/L), bleeding event, and treatment modification/initiation (and 95% CI), respectively, was estimated with the Kaplan-Meier method and compared in the 2 groups with the use of a Cox model with shared frailty. ∗Except treatment to prepare delivery.