Women are twice as likely to develop gallstones as men because of the effects of estrogen and progesterone. Gallbladder emptying may be slowed by progesterone, a normal hormone secreted during the second half of the menstrual cycle and during pregnancy. Estrogen and progesterone affect the handling of cholesterol in the body. Because of the slowed emptying of the gallbladder as well as an increase of cholesterol in the gallbladder, there is a greater chance for the development of gallstones.