From Pages to Practice

By James Yeh, MD, MPH

Published January 5, 2022


Several maternal physiological changes occur during pregnancy. Thrombocytopenia (defined as a platelet count below the 2.5th percentile of the normal range, with a count of 150,000 per cubic millimeter as a traditional cutoff for the lower limit) is thought to occur in up to 10% of all pregnancies. However, the incidence, onset, and severity of thrombocytopenia during pregnancy is not well defined. Evaluation and management of thrombocytopenia during pregnancy can be difficult because potential causes range from gestational thrombocytopenia — the most common cause and thought to be a self-limiting — to HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets), which can cause serious complications in both the mother and the fetus and may require urgent interventions.

What is the study about?

In a retrospective cohort study, investigators analyzed platelet counts in approximately 7351 women ages 15–44 years with 15,723 deliveries at a single medical center in Oklahoma between 2011 and 2014, and compared them with platelet counts in 8885 nonpregnant women with similar demographics in the National Health and Nutrition Examination Survey (NHANES).

Of the 7351 women who delivered, most had an uncomplicated pregnancy (4568 women), about one-third had pregnancy-related complications (2568 women), and about 2.5% (187 women) had a pre-existing disorder associated with thrombocytopenia.

Among the women with uncomplicated pregnancies, the mean platelet count declined throughout the course of pregnancy. In the first trimester, the mean platelet count was lower in pregnant women with uncomplicated pregnancies than in nonpregnant women (251,000 vs. 273,000 per cubic millimeter; P<0.001). At the time of delivery, about 10% of women with uncomplicated pregnancies had platelet counts <150,000 per cubic millimeter and about 1% had platelet counts <100,000 per cubic millimeter. Significantly more women with preexisting disorders associated with thrombocytopenia had platelet counts <80,000 per cubic millimeter during pregnancy, at the time of delivery, or both than women with uncomplicated pregnancies (9% vs. 0.3%).

What is my take away?

Platelet counts decreased during pregnancy starting in the first trimester. About 10% of the women with uncomplicated pregnancy had platelet counts <150,000 per cubic millimeter at the time of delivery. In pregnant women with platelet counts <80,000 per cubic millimeter, an underlying cause of the thrombocytopenia should be sought.

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James Yeh, MD MPH, Physician at NEJM Group
James Yeh, MD MPH is an internist and assistant in medicine at the Massachusetts General Hospital and an instructor in medicine at Harvard Medical School. His clinical and academic interests are in evidence-based medicine, medical education, continuing medical education, cardiopulmonary diseases, cardiovascular risk reduction, critical illness, care transition, polypharmacy, and health communication. He was a NEJM editorial fellow in 2015-2016.