Background: Intrahepatic cholestasis of pregnancy, characterised by maternal pruritus and raised serum bile acid concentrations, is associated with increased rates of stillbirth, preterm birth and neonatal unit admission. Ursodeoxycholic acid is widely used as a treatment, but without an adequate evidence base. Objective: We aimed to evaluate whether or not ursodeoxycholic acid reduces adverse perinatal outcomes in affected women. Design: Multicentre, masked, randomised, placebo-controlled, two-arm, parallel-group trial. Setting: Thirty-three UK maternity units. Participants: Women with intrahepatic cholestasis of pregnancy aged ≥ 18 years, between 20+0 and 40+6 weeks’ gestation with a singleton or twin pregnancy and no known lethal fetal anomaly. Interventions: Women were randomly assigned (1 : 1 allocation ratio) to take ursodeoxycholic acid tablets or matched placebo tablets, at an equivalent dose of 1000 mg daily, titrated as needed. Main outcome measures: The primary outcome was a composite of perinatal death (in utero fetal death after randomisation or known neonatal death up to 7 days) or preterm delivery (