You are answering a USMLE-style medical question. Question: A 29-year-old G4P0 woman presents following a spontaneous pregnancy loss in the 18th week of her pregnancy. This is her fourth loss in the second trimester and she is concerned about her inability to have a successful pregnancy. She is otherwise healthy and has no acute complaints. Her vitals are unremarkable and exam is notable only for a firm, asymmetric uterus. Laboratory studies are ordered as seen below. Hemoglobin: 9.0 g/dL Hematocrit: 30% Leukocyte count: 6,800/mm^3 with normal differential Platelet count: 199,000/mm^3 Serum: Na+: 139 mEq/L Cl-: 100 mEq/L K+: 4.3 mEq/L HCO3-: 25 mEq/L BUN: 20 mg/dL Glucose: 99 mg/dL Creatinine: 1.1 mg/dL Which of the following tests is most likely to elucidate the cause of this patient's pregnancy losses? Options: A) Karotyping B) Hysterosalpingogram C) Prolactin level D) TSH level Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.