Effect of long-term use of Norplant® implants on haemostatic function

Abstract

This study describes the effects of Norplant® on haemostatic function after 5 years of use in 97 women. There was a decrease in vitamin-K dependent Factors II, V, VII and reduction in fibrinolytic activity at 2 and 4 years of use. Increased platelet numbers and accelerated platelet aggregation were found throughout the 5 years of Norplant® use, whilst raised alpha2-Macroglobulin (α2-M) and antithrombin III (ATIII) antigen level were observed for up to 4 years of use. Prolonged Norplant® use does not appear to activate the coagulation system and does not enhance a state of hypercoagulation.

The effect of 5 years' use of Norplant on blood clotting factors was assessed in 97 Singaporean women. The subjects were healthy, non-smoking non-alcohol drinking and non-lactating. Blood was sampled at 6, 12, 18, 24, 36, 48 and 60 months, after an overnight fast, and resting 30 minutes before venipuncture. Hemoglobin and hematocrit increased 10% in the 1st year (p0.001), fell for the next 2 years, reaching pre-insertion levels by 3 years, then increased 10% for the last 2 years. There was a significant shortening of the prothrombin time (PT) throughout the 5 years, and of activated partial thromboplastin time (APTT) for 3 years. Vitamin K-dependent Factors II, V, VII, decreased throughout the 5 years, and fibrinolytic activity decreased at 2 and 4 years of use. Fibrinogen increased at the end of the 1st year only. Platelet numbers rose 25.6% to 43.4%, and platelet aggregation to both ADP and collagen increased throughout the 5 year period. Alpha2-macroglobulin and antithrombin III antigen levels were heightened for 4 years. Most of the observed changes were different from those seen in oral contraceptive users, except for alterations in platelet function. While some of the measured clotting factors were significantly different, none were of any clinical significance, nor were these women in a state of hypercoagulation.