Risk Factors of Neonatal Immune Thrombocytopenia in Pregnant Women Previously Diagnosed with ITP: Results from a French Nationwide Prospective Study

Background: Neonatal immune thrombocytopenia (NITP) is a well described complication in newborns of women with ITP. It is reported to occur in about 15% to 30% of neonates. Previous pregnancies with NITP or ITP refractory to splenectomy have been described as associated with NITP mostly in retrospective studies. Methods: We conducted a nationwide prospective multicenter observational case-control study (ClinicalTrials.gov NCT02892630). Thirty-three centers including in the network of ITP experts in France participated in the study. Over a two years period, we enrolled 180 pregnant women with a history of ITP diagnosed before pregnancy and 171 of them were followed up until the delivery. Neonatal platelet counts were available for 136 newborns. Risk factor for developing NITP were evaluated as well as NITP treatment and complications. Results: NITP defined as a platelet count < 100 x 10⁹/L was observed in 37 newborns (27.2%). More severe NITP with platelet counts < 50 x 10⁹/L and < 30 x 10⁹/L, were reported in 19 (14%) and 13 (9.6%) newborns respectively. Intravenous immune globulins were given to 18 newborns. Their median platelet count was 25.5 x 10⁹/L (6; 56). Platelet transfusion was used for 8 newborns with a median platelet count of 13.5 x 10⁹/L (6; 50). NITP was complicated by a hemorrhagic event in only 2 newborns, with a fatal bleeding in 1. Decline in disease ITP status in the mother during pregnancy and previous history of NITP were identified as predictors of NITP < 50 x 10⁹/L by a univariate analysis while only previous history of NITP was confirmed in multivariate analysis (adjusted odds ratio (OR) 4.55; 95% confidence interval (CI) 1.48-13.92; p= 0.008). Decline in ITP disease status in the mother during pregnancy was the sole predictive factor for severe NITP defined as platelet < 30 x 10⁹/L in multivariate analysis (adjusted OR 3.99; 95% CI 1.04-15.36; p = 0.044). Conclusion: Our study confirms that for ITP women with several pregnancies, a previous history of NITP is a risk factor for NITP. We also identify for the first time worsening of disease status during pregnancy to be a novel risk factor of severe NITP. In contrast, we did not confirm that a history of splenectomy was associated with an increased risk of NITP as suggested in retrospective studies (Loustau et al, Br J Haematol 2014; 166 929-35). Our results support that pregnancy in women with ITP is associated with an acceptable risk of severe bleeding in the newborn with NITP which is low but yet existing. Hence, close monitoring of pregnancy and delivery of mothers with ITP and their newborns is required, mainly in women who have a previous history of NITP or experienced a worsening of ITP during the pregnancy.