A 28-year-old primigravida presents for first-trimester antenatal ultrasound at 12 weeks gestation. The sonographer identifies a fetus with a characteristic appearance: the structure marked **A** (absent cranial vault above the orbits) is noted, along with prominent "frog-eye" orbits and exposed neural tissue. The patient has no prior obstetric history and denies antiepileptic drug use. Which of the following is the most appropriate next step in counseling and management?