A 32-year-old primigravid woman at 9 week’s gestation has had severe nausea and cannot keep anything in her stomach for the past 2 days. She has had vomiting and mild nausea for the past month. Examination is unremarkable. Ultrasonography shows a crown-rump length consistent with a 10-week gestation pregnancy. Which of the following is the next best step in diagnosis?
Complete blood count
GDF15 and IGFBP7 genotyping
Hemoglobin electrophoresis
Quantitative β-hCG serum assay
Serum TSH
Urinary ketones
