The effect of progesterone on the haemostatic mechanism

The hemostatic effect of progesterone administered vaginally at a dose of 100 mg twice a day throughout one menstrual cycle was investigated and compared with the coagulation factors in one untreated normal menstrual cycle in 15 women. The progesterone treatment resulted in a 20-fold progesterone rise in the early follicular phase from 1.2 nmol/l in the pretreatment control cycle to levels between 26 and 29 nmol/l during treatment. Ovulation was completely suppressed in seven women while eight women showed a slight rise in progesterone on treatment days 20 to 25 not compatible with the rise which could have been expected if ovulation had occurred. The effects found on haemostasis during progesterone treatment varied with the menstrual cycle and were so small that they could as well be due to chance and not to treatment.