Hemostatic changes in women using a monthly injectable contraceptive for one year

The effect of consecutively injecting a one-a-month contraceptive (norethisterone enantate 50 mg with estradiol valerate 5 mg) for one year on haematological parameters was evaluated in 42 Chinese women. The healthy volunteers were randomly allocated to either the treatment group (22) or a control group (20). Blood samples were collected in the follicular and luteal phases of a pretreatment cycle, on days 28 +/- 3 after the 1st, 3rd, 6th, 12th injections and in the luteal phase of the post-treatment cycle. The results showed that in both groups, prothrombin time and fibrinogen fluctuated significantly, and leucocyte count was not significantly changed during the whole course. Factor VIII-related antigen and antithrombin III (AT-III) antigen showed minor changes, although in the 3rd treatment cycle, the differences between the two groups in both parameters reached statistical significance. A progressive and significant decrease in Factor X and AT-III functional activity occurred with the monthly injectable treatment, decreasing by about 14% and 20%, respectively, after 12 months of treatment. Haemoglobin levels were increased in the treatment group after the 3rd injection and remained at the higher level during the study period. It is doubtful whether these changes are likely to be of clinical relevance.