Hemorheological effects of oral contraceptives.

To determine the hemorheological effects of oral contraceptives, 50 healthy young women took no medication for 3 cycles. Subsequently they were randomized into group A and B. Group A took Diane-35, B took Microgynon each for 6 cycles. Finally 3 cycles without medication followed. Blood viscosity was quantified by ex vivo measurements of hematocrit, blood and plasma viscosity, red cell filterability, fibrinogen and colloid oncotic pressure. In group A fibrinogen rose at the end of the medication phase. In group B fibrinogen, blood and plasma viscosity increased on medication. The former 2 variables remained elevated even after discontinuation of the oral contraceptive. The data combined with those from the literature suggest that low-dose oral contraceptives lead to no biologically meaningful changes in blood rheology while higher doses induce limitations of blood fluidity which could be involved in the increment of cardiovascular risk by these medications.