A 16-year-old girl arrives at the office for her first prenatal visit. After missing her period, she took two home pregnancy tests, both of which were positive, and came in a week ago for a blood test. The blood test also was positive. Today she appears pale and apprehensive, and asks, "Is there any other kind of test I can take, just to make sure?" Which of the following would be the most accurate nursing diagnosis of this patient?