Step 1: Read the stem carefully; we need the one statement that does NOT fit intrahepatic cholestasis of pregnancy. This is a negative-lead question, so a true-sounding fact may still be the answer if it is actually incorrect.
Step 2: Go through each option as true or false. A bilirubin above $2$ mg% can occur in ICP, that is true. High oestrogen and progesterone impair bile flow and trigger the disease, that is true. The clinical picture, mainly itching, surfaces in the third trimester and resolves postpartum, that is true.
Step 3: The remaining claim is that ICP is the commonest cause of jaundice in pregnancy. This is incorrect. Across all pregnant women the leading cause of jaundice is viral hepatitis. Cholestasis of pregnancy is merely the commonest cause among the pregnancy-unique liver disorders, not of jaundice overall.
Step 4: The statement that is false, and hence the required answer, is that cholestasis is the most common cause of jaundice in pregnancy.
\[\boxed{\text{Most common cause of jaundice in pregnancy}}\]