Platelet counts decrease during pregnancy. In some women, platelet levels may fall below the normal range even when there are no pregnancy complications. In other cases, low platelet counts are caused by pregnancy complications such as preeclampsia, or by preexisting conditions that become worse during pregnancy. Therefore, it is important to understand how platelet levels change throughout pregnancy, and the relationship between platelet counts and pregnancy complications.

This study was the first to define the course of platelet counts throughout pregnancy. The study leveraged electronic medical record data to analyze changes in platelet counts throughout 4,568 uncomplicated pregnancies, 2,586 pregnancies with complications, and 197 pregnancies in women with preexisting conditions associated with thrombocytopenia (low platelet counts). It was previously assumed that platelet counts begin to decrease in the mid-second or early third trimester, and continue to decrease until the time of delivery. However, this study showed that platelet counts decrease throughout pregnancy, beginning in the first trimester. By the time of delivery, approximately 10% of women with no pregnancy complications had low platelet counts (

This study relied on infrastructure that was developed with OSCTR support. The data for the study came from the Clinical Data Warehouse developed and maintained by the OSCTR Clinical Resources Core and Biostatistics, Epidemiology, and Research Design (BERD) Core. Compared to previous studies, this was a larger and more detailed population-based study of platelet counts during pregnancy, which would not have been possible without the Clinical Data Warehouse. Four of the eight study authors have received support and gained relevant expertise from the OSCTR. Three are personnel within the BERD Core, and one previously served as Director of the Professional Development Core. Finally, two of the authors specialized in the OSCTR Translating Practice into Research Program, which trains clinicians in a structured approach to translating clinical concerns into research questions.

Reference: Reese JA, Peck JD, Deschamps DR, McIntosh JJ, Knudtson EJ, Terrell DR, Veseley SK, and George JN. Platelet counts during pregnancy. N Engl J Med. 2018 Jul 5; 379(1): 32–43.