Progesterone supplementation has been used in a large number of women with threatened abortion for decades, despite various degrees of success, and contradictory and ever-changing views about its efficacy. The majority of previous literature has mainly focused on evaluation the effect of progesterone on pregnancy outcome of threatened abortion. No controlled epidemiological studies of obstetric and perinatal outcomes, including preterm birth, pregnancy complications and low birth weight newborns, in pregnant women with progesterone treatment have been published. The data of 523 pregnant women with progesterone treatment in the second and third months of pregnancy due to threatened abortion was compared with the data of other 21,054 pregnant women in the Department of Obstetrics, West China Second University Hospital for a period of 6years from January 2002 to October 2008. There was no difference in mean gestational age at delivery and birth weight, in addition the rate of preterm birth, pregnancy complications and low birth weight newborns. Intramuscular progesterone treatment due to threatened abortion during early pregnancy did not associate with a higher risk for pregnancy complications, preterm birth and low birth weight newborns.