Effect of the menstrual cycle, oral contraception and pregnancy on forearm blood flow, venous distensibility and clotting factors.

Forearm blood flow, venous distensibility and various clotting factors were determined in 118 apparently healthy women (mean age 26 years), either during the menstrual cycle, or while taking a combined contraceptive (A) with high progestin:estrogen ratio (d-norgestrel 0.125 mg + ethinylestradiol 0.03 mg), or a sequential contraceptive (B) with low progestin: estrogen ratio (megestrol 0.1/1 mg + ethinylestradiol 0.1 mg), or in the 1st, 2nd and 3rd trimester of pregnancy. Venous distensibility in women taking contraceptive A was higher than in other women during the follicular phase of a normal menstrual cycle. Venous distensibility was not affected by contraceptive B. Blood flow and blood pressure remained unchanged by contraceptives A and B. Fibrinogen concentration was increased by both contraceptives, factor VII was either decreased (A) or unchanged (B), and factor X was either unchanged (A) or increased (B). The oral contraceptive with the high progestagen component appeared to increase venous capacitance and may induce venous stasis, whereas coagulability was particularly enhanced by the estrogen-type contraceptive. Pregnant women differed from women on oral contraceptives in regard to peripheral circulation; they showed a tremendous increase of blood flow with secondary vasodilation.