Post-partum hemorrhage (PPH) is one of the main direct causes of maternal mortality, particularly in rural areas with low access to skilled providers, blood banks, and surgical facilities. In addition to the mortality, PPH also accounts for a great number of morbidities, including anemia, renal and pulmonary problems, fatigue, and decreased resistance to infection, all major health problems affecting women in the TAR. Clinical research is rare in the Tibetan Autonomous Region (TAR) of the People's Republic of China. This trial will estimate the effect of prophylactic oral ZB 11 administered at the beginning of the second stage of labor versus prophylactic oral misoprostol, administered in the third stage of labor, in reducing the incidence of postpartum hemorrhage (defined as a measured blood loss of > 500 cc).