A 6-week pregnant woman has Hb 9.8, MCV 72, ferritin 42. What is the best next step?

• A. Start iron therapy
• B. Hemoglobin electrophoresis for thalassemia trait
• C. Blood transfusion
• D. Bone marrow biopsy

Answer: (B)

Distinguishing iron-deficiency anemia from a hemoglobinopathy in pregnancy. The combination of a low hemoglobin with microcytosis (low MCV) and a ferritin level that is not frankly low points away from iron deficiency as the sole cause. Ferritin around the low-normal range suggests iron stores are not depleted, so you should pursue a test that can identify a hemoglobinopathy, such as thalassemia trait, rather than assuming iron deficiency is driving the anemia.

Hemoglobin electrophoresis is the best next step because it can reveal elevated HbA2 (and sometimes HbF) that characterizes beta-thalassemia trait, or otherwise guide diagnosis of a hemoglobinopathy. Confirming a thalassemia trait changes management: you generally wouldn’t treat with iron unless iron deficiency is proven, and there’s no indication for transfusion or invasive bone marrow biopsy in this scenario.

So, the goal is to confirm whether a thalassemia trait explains the microcytosis and mild anemia, guiding appropriate management and counseling.