It is unclear whether neonates born to women with thrombocytopenia during pregnancy are themselves at increased risk for thrombocytopenia at birth. In the current retrospective study, platelet count reference ranges were developed for pregnant women according to trimester, and correlations were sought between the platelet counts of mothers at delivery and their neonates. During the study period, 92,518 platelet counts were recorded on 41,887 pregnant women. A progressive shift toward lower platelet counts in a similarly shaped histogram occurred during pregnancy, with the lower reference range (2.5 percentile) for platelets during the third trimester being 113 × 10(9)/L. Among 11,797 maternal-neonatal pairs following delivery, no correlation was observed between maternal and neonatal counts. However, if the mother's lowest count was <50 × 10(9)/L, the relative risk of any degree of thrombocytopenia in their neonate was 4.6 (95% confidence interval [CI], 1.8 to 33.3) and the relative risk of severe neonatal thrombocytopenia was 7.8 (95% CI, 1.8 to 33.3). The results of the current study demonstrate that platelet counts >75 × 10(9)/L in pregnant women were not associated with an increased risk of neonatal thrombocytopenia, and maternal platelet counts of <50 × 10(9)/L were accompanied by an almost fivefold risk increase of neonatal thrombocytopenia.
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