A 35-year-old woman at 35 weeks of pregnancy presents with vomiting, malaise and jaundice. She is normotensive, has no proteinuria and has mild right upper quadrant tenderness. Bilirubin is 96 micromol/L (3–20), alanine aminotransferase 310 U/L (5–40), glucose 2.4 mmol/L (3.5–7.8), platelet count 178 × 10⁹/L (150–400) and international normalised ratio 1.8 (0.8–1.2). Ultrasound shows no biliary obstruction. Which one of the following is the most likely diagnosis?