D is the correct answer

Thrombocytopenia is defined as a platelet count < 150,000/μL and occurs in 7–12% of pregnancies. The most common etiology is gestational thrombocytopenia, which accounts for 80% of cases. It can occur at any point in the pregnancy but usually is in the mid-second and third trimesters. The platelet count is typically > 75,000/μL, but some cases describe a platelet count as low as 43,000/μL. These women are asymptomatic and have a normal platelet count outside of pregnancy. Thus, to confirm the diagnosis of gestational thrombocytopenia, a repeat platelet count at 4–12 weeks after delivery will demonstrate resolution of the platelet count. It is believed that gestational thrombocytopenia occurs from a physiologic adaptation of pregnancy. As plasma volume increases up to 50%, a hemodilution effect results in decreased platelet count per liter of blood. Enhanced platelet clearance may also be a contributing factor. Gestational thrombocytopenia is likely to recur with subsequent pregnancies.

Immune thrombocytopenia occurs due to impaired platelet production and reduced platelet lifespan, but the platelets themselves function normally. It occurs by an autoimmune process (A) of IgG autoantibodies from the B cells against glycoprotein IIb-IIIa integrin complex on platelets. The platelet count can be < 50,000/μL. Management during pregnancy includes prednisone 10–20 mg/day initially and then adjusting to the smallest dose that achieves an adequate platelet count. Preeclampsia is the second most common cause of thrombocytopenia, accounting for 5–20% of cases. The platelet count is usually < 100,000/μL due to platelet activation, resulting in a consumptivecoagulopathy (B). Thrombotic thrombocytopenic purpura is a rare blood disorder of deficient von Willebrand factor-cleaving protease (ADAMTS13) protease (C), which normally cleaves von Willebrand factor multimers, resulting in an uninhibited clotting cascade. Treatment includes plasma exchange or steroids.