A 28-year-old woman attends the antenatal clinic with a history of amenorrhea for 6 weeks. She reports regular 28-day menstrual cycles and is certain of her last menstrual period (LMP), which was 6 weeks ago. On clinical examination, the uterus is palpable just above the symphysis pubis. Serum β-hCG is 25,000 mIU/mL. Transvaginal ultrasound shows a gestational sac of 8 mm diameter with a yolk sac visible. Which of the following best describes the gestational age and dating method used in this case?