A 35-year-old primigravida at 38 weeks of gestational age has a blood pressure reading of 150/100 mm Hg obtained during a routine visit. Her baseline blood pressure during the pregnancy was 120/70 mm Hg. The patient denies any headache, visual changes, nausea, vomiting, or abdominal pain. Her repeat BP is 160/90 mm Hg, and urinalysis is negative for protein. Which of the following is the most likely diagnosis?