Estimation of the risk of thrombocytopenia in the offspring of pregnant women with presumed immune thrombocytopenic purpura.

BACKGROUND AND METHODS: The optimal management of immune thrombocytopenic purpura during pregnancy remains controversial because the risk of severe neonatal thrombocytopenia remains uncertain. We studied the outcome of the index pregnancy in 162 women with a presumptive diagnosis of immune thrombocytopenic purpura to determine the frequency of neonatal thrombocytopenia and to determine whether neonatal risk could be predicted antenatally by history or platelet-antibody testing.

RESULTS: Two maternal characteristics were identified as predicting a low risk of severe neonatal thrombocytopenia: the absence of a history of immune thrombocytopenic purpura before pregnancy, and the absence of circulating platelet antibodies in the women who did have a history of the condition. Eighteen of 88 neonates (20 percent; 95 percent confidence interval, 13 to 30 percent) born to women with a history of immune thrombocytopenic purpura had severe thrombocytopenia (platelet count less than 50 x 10(9) per liter at birth), as compared with 0 of 74 (0 percent; 95 percent confidence interval, 0 to 5 percent) born to women first noted to have thrombocytopenia during pregnancy (P less than 0.0001). Among the women with a history of immune thrombocytopenic purpura, 18 of 70 neonates (26 percent; 95 percent confidence interval, 16 to 38 percent) born to those with circulating platelet antibodies had severe thrombocytopenia, as compared with 0 of 18 infants (0 percent; 95 percent confidence interval, 0 to 18.5 percent) born to those without circulating antibodies (P less than 0.02). Thus, the risk of severe neonatal thrombocytopenia in the offspring of women without a history of immune thrombocytopenic purpura before pregnancy and of women with a history of the condition in whom circulating platelet antibodies are not detected was 0 percent (95 percent confidence intervals, 0 to 5 and 0 to 18.5 percent, respectively).

CONCLUSIONS: The absence of a history of immune thrombocytopenic purpura or the presence of negative results on circulating-antibody testing in pregnant women indicates a minimal risk of severe neonatal thrombocytopenia in their offspring.