Mean platelet counts shown to decrease during pregnancy

1. Retrospective analyses demonstrated evidence of mean platelet count decline during pregnancy beginning as early as the first gestational trimester

2. Platelet counts were significantly lower among patients with documented pregnancy-related complications as compared to women with uncomplicated pregnancies.

Evidence Rating Level: 2 (Good)

Study Rundown: Gestational thrombocytopenia is defined by an incidental drop in platelet counts at the time of delivery to below 150 000 per cubic millimeter (/mm³). While gestational thrombocytopenia is generally accepted to be the result of various physiologic changes that occur during pregnancy, data on how platelet counts change throughout the course of pregnancy have not yet been well defined. The objectives of the current analysis were three-fold: to compare trends in platelet counts during pregnancy to nonpregnant states, to better understand how various pregnancy-related complications affect platelet counts during gestation, and to assess how known conditions associated with thrombocytopenia affect platelet counts during pregnancy. Platelet counts from the first trimester, second trimester, third trimester, delivery, and postpartum gestational intervals were specifically compared. Overall, platelet counts decreased throughout the course of pregnancy among all pregnant women studied, beginning as early as the first trimester. Platelet counts were significantly lower among pregnant individuals as compared to non-pregnant individuals, as well as among women with pregnancy-related complications as compared to women with uncomplicated pregnancies.

Strengths of the study include the large number of patients and comparison with a national database of nonpregnant women. Notable limitations included single institution data collection and limited number of patient related variables assessed.

Click to read the study, published in NEJM

Relevant Reading: Platelet counts in women with normal pregnancies: A systematic review.

In-Depth [retrospective cohort]: This retrospective cohort study compared data on pregnant women aged 15-44 who delivered at a single academic medical center between 2011 through 2014 to data of nonpregnant women obtained from the National Health and Nutrition Examination (NHANES) database from 1999 through 2012. A total of 7351 women from the Oklahoma University Medical Center cohort were included for analysis, of which 4568 had an uncomplicated pregnancy, 2586 had a pregnancy-related complication, and 197 had preexisting conditions associated with thrombocytopenia. Women with documented uncomplicated pregnancies were noted to have significantly lower mean platelet counts compared to non-pregnant women during each trimester and at time of delivery (251 000/mm³ in first trimester; 230 000/mm³ in the second trimester; 225 000/mm³ in the third trimester; 217 000/mm³ at delivery; 273 000/mm³ non-pregnant; p < 0.001). Platelet counts were estimated to be 17% lower at time of delivery compared to the post-partum period (218 000 vs 264 000/mm³, respectively). Trend analyses demonstrated the documented decrease in platelet counts throughout pregnancy was significant (p < 0.001). Similarly, women with documented pregnancy-related complications and thrombocytopenic conditions also demonstrated significant decreased trends in mean platelet counts during pregnancy (p < 0.001 for both analyses, respectively). Women with pregnancy complications were more likely to have platelet counts less than 150,000 per cubic millimeter compared to women with uncomplicated pregnancies (11.9% vs 9,9% respectively; p = 0.01).

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