An 18-year-old primigravid woman comes for her initial prenatal visit at 16 weeks' gestation. She is not sure about the date of her last menstrual period but says that the pregnancy probably occurred immediately after she stopped taking oral contraceptives 5 months ago. Maternal serum α-fetoprotein (MSAFP) level is increased to 3 multiples of the median. Which of the following is the most appropriate next step in management? a. Repeat measurement of MSAFP level
b. Triple screening for MSAFP, serum β-hCG, and serum estriol levels
c. Ultrasonography
d. Amniocentesis for measurement of α-fetoprotein level
e. Amniocentesis for chromosomal analysis