What causes cholestasis of pregnancy is unclear. There may be a genetic component, as the condition sometimes runs in families and certain genetic variants have been associated with it.

Pregnancy hormones also may play a role. Bile is a digestive fluid produced in the liver that helps the digestive system break down fats. It's possible that the increase in pregnancy hormones — such as occurs in the third trimester — may slow the normal flow of bile out of the liver. Eventually, the buildup of bile in the liver allows bile acids to enter the blood stream. Bile acids deposited in the mother's tissues can lead to itching.

Aug. 16, 2014