Abstract: ObjectiveTo study the effects of long2term usage of low-dose norethisterone(Chinese No.1)and 18-metaylnorethisterone(Norgestrel)on the blood coagulation system of heathy women.MethodsOne hundred and forty one women were grouped as combined norethisterone(Chinese No.1),combined 18-metayl-norethisterone(Norgestrel)using them for 515years,and control subjects wearing IUD for the corresponding period.The activity of coagulation factors Ⅱ、Ⅴ、Ⅶ、Ⅷ、Ⅹ and APTT、PT-FIB(A)、PT-FIB(B)、TT were measured in the three groups.ResultsThe activated partial thromboplastin time (APTT)in the two groups were accelerated,having a statistically significant increase in the Chinese No.1 group.Factor X activity in two groups was significantly higher than that in control group(P<0.05,P<0.01).Factor Ⅷ activity in the Chinese No.1 group increased significantly compared with control group(P<0.05).Other parameters tested in three groups were similar except that Factor Ⅶ increased in the Chinese No.1 group,but decreased in the Norgestrel group(P>0.05).ConclusionLong-term usage of Chinese low-dose COCs had a slight negative influence on haemol-stati,the small differences in level of coagulation factors of the two COCs may depend on the dosage of estrogen and the type of progestogen used in combination.However,in the present situation,these changes did not exceed the variation seen in healthy women who did not use COCs,and had no clinical relevance.