A 32-year-old woman is confirmed as being 6 weeks pregnant. She feels well, and has no past medical history. This is her second pregnancy; the first pregnancy was uncomplicated and she delivered at term, but the baby was anemic due to beta-thalassemia. She is now worried that the current pregnancy may also be affected. Which of the following methods is most likely to establish an accurate prenatal diagnosis?
fetal ultrasound at 12 weeks cord blood electrophoresis chorionic villus sampling buccal mucosal cytology of both parents