A 22-year-old primigravid African American woman comes to the physician for her first prenatal visit. She has no complaints. Her last menstrual period was 7 weeks ago. Past medical history is significant for sickle cell trait. Her partner is also known to have sickle cell trait. She takes no medications and has no allergies to medications. Physical examination is unremarkable except for a mildly enlarged uterus consistent with early pregnancy. Which of the following represents this couple's risk of having a child with sickle cell anemia? (A) 0% (B) 25% (C) 50% (D) 75% (E) 100%