Your Patient Comes for Her First Prenatal Visit on May

Your patient comes for her first prenatal visit on May 13. She is sure of her last menstrual period (LMP) , which was December 31. She states that she remembers getting her period because she was at a party that night and it was a normal period for her in flow and length. Her an estimated gestational age by LMP is 19 weeks today. When reviewing her medical record you note that she had a fetal survey ultrasound done on May 8 giving her a gestational age of 19 weeks (7 days different from her LMP date) . On her abdominal exam at today's visit her uterine size is 20 weeks. Which of the following would you use to establish the best estimate of the delivery date (EDD) ?

A) Last menstrual period
B) Ultrasound
C) Uterine size