Thrombocytopenia in pregnancy: Differential diagnosis can be life-saving

When a prenatal screening report tells you that a patient's platelet count is low, sorting out the differential diagnosis of this bleeding disorder can seem daunting. Is it a relatively benign problem like gestational thrombocytopenia or a less common disorder that can lead to life-threatening bleeding, such as disseminated intravascular coagulation (DIC) or acute fatty liver? Our goal here is to clarify the path to an accurate diagnosis.

Thrombocytopenia affects roughly one in 10 pregnant women, making it a leading reason for ob/gyns to consult a perinatal hematologist.¹ The normal range of platelet counts is from 150,000 to 400,000/μL in the nonpregnant woman and may be slightly lower in pregnant women secondary to greater expansion of their plasma volume, RBC, and platelet number, with resultant hemodilution.

The obvious concern with thrombocytopenia during pregnancy is significant bleeding at the time of vaginal or cesarean delivery. Fortunately, such bleeding complications are uncommon unless the platelet count is less than 50,000/μL at the time of surgery or delivery.^2,3 Early signs of a low platelet count include gingival bleeding, epistaxis, petechiae, and easy bruising. However, in the absence of trauma or surgery, significant bleeding is rare unless platelet counts are less than 10,000/μL.

Gestational thrombocytopenia

First defined in 1986, gestational thrombocytopenia is now recognized as the most common cause of thrombocytopenia in pregnancy, accounting for 74% of cases.⁵ The second chief cause is preeclampsia/HELLP (hemolysis/elevated liver enzymes/low platelets) syndrome, comprising 21% of cases, followed by idiopathic thrombocytopenic purpura (ITP) which accounts for just 5% of thrombocytopenic patients.¹

Typically, gestational thrombocytopenia is identified on a routine prenatal complete blood count screen. The patients are usually asymptomatic and have mild thrombocytopenia (platelet counts usually above 70,000/μL). Researchers have reported that 97% of thrombocytopenic pregnant women with platelet counts above 115,000 had gestational thrombocytopenia, whereas only 47% of those with platelet counts less than 75,000 had this diagnosis.⁶

With gestational thrombocytopenia, there are no associated signs or medical complications such as petechiae or bleeding. Preeclampsia and HELLP syndrome should be ruled out, however. Unfortunately, though, further laboratory evaluation for antiplatelet antibodies cannot separate gestational thrombocytopenia from ITP or HELLP syndrome.

Two things confirm the diagnosis of gestational thrombocytopenia:

(1) the incidental finding of thrombocytopenia on CBC in an asymptomatic pregnant patient with no significant past coagulopathy, and

(2) resolution of the platelet count to normal in the postpartum period.

Once you rule out preeclampsia in an otherwise healthy parturient, platelet counts above 100,000/μL require no further evaluation.

On the other hand, if the platelet count falls below 70,000/μL, seek other causes and follow complete blood counts until you deem the platelet count stable.⁷ Although pregnant women with gestational thrombocytopenia can have antiplatelet antibodies, thrombocytopenia poses little-to-no risk of neonatal morbidity^8-10 and no increased risk of maternal hemorrhage. Therefore, provide routine prenatal care to women with gestational thrombocytopenia. And keep in mind that this benign condition has been reported to recur in subsequent pregnancies.¹¹