Contraceptives and hormone replacement have been extensively used since the late 1950s. However, adverse effects are common and include an increased risk of cardiovascular diseases, including thrombo-embolic diseases. Previous research has shown that ultrastructure of fibrin networks may provide great insight regarding the thrombotic potential of patients. The current study investigates the scanning electron microscopy (SEM) ultrastructure of fibrin networks of individuals using oral contraceptive therapy as well as individuals using hormone replacement. We compare micrographs of these two groups with micrographs of young, healthy individuals not using oral contraception. Platelet rich plasma and thrombin was used to prepare the fibrin clots. Here we show that during contraceptive and hormone replacement use, a netted fibrin layer forms. We suggest that oestradiol use causes fibrin network changes and these changes can be seen using SEM technology. These changes may provide further evidence regarding the increased occurrence of thrombotic events during contraceptive and hormone replacement therapy.