Endogenous thrombin potential is higher during the luteal phase than during the follicular phase of a normal menstrual cycle

• Do thrombin generation and haemostatic parameters differ during the two phases of the menstrual cycle? less thanbrgreater than less thanbrgreater thanTotal thrombin concentration is higher during the luteal phase compared with the follicular phase of the menstrual cycle. less thanbrgreater than less thanbrgreater thanThe coagulation cascade is affected by many variables, such as fluctuations in the levels of sex hormones. The studies on the variations in haemostatic parameters during the menstrual cycle have produced diverse results. less thanbrgreater than less thanbrgreater thanThrombin generation and selected haemostatic parameters (fibrinogen, factor II, factor VII, factor VIII, factor X, von Willebrand factor, antithrombin and D-dimer) were measured during the two phases of a normal menstrual cycle in 102 healthy women not taking any form of hormone medication. less thanbrgreater than less thanbrgreater thanThe study cohort consisted of 102 healthy women with regular menstrual cycles. Thrombin generation was measured by the calibrated automated thrombogram method. Progesterone and sex hormone-binding globulin were measured by chemiluminescence enzyme immunoassays. Estradiol was measured by a sensitive radioimmunoassay. Fibrinogen was measured by a clotting method, antithrombin was measured by a chromogenic method and factor II, factor VII, factor VIII, factor X, von Willebrand factor and D-dimer were measured by photometric methods. less thanbrgreater than less thanbrgreater thanIt was shown that the total amount of generated thrombin (Endogenous Thrombin Potential) was significantly higher during the luteal compared with the follicular phase (P 0.027). Factor X was significantly higher during the follicular phase (P 0.028). Progesterone exhibited significant associations (measured by the least squares regression analysis) with fibrinogen and factor X during the follicular phase (P 0.043 and P 0.033, respectively) and with factors II and VII during the luteal phase (P 0.034 and P 0.024, respectively). The validity of the results from the regression analysis was further confirmed by performing correlation analyses (Pearson correlation matrix) for haemostatic markers for the luteal and follicular phases (accepted correlation level 0.8). less thanbrgreater than less thanbrgreater thanThe wide confidence interval for the differences in endogenous thrombin potential during the two phases could imply that the size of the cohort may not be sufficient to fully evaluate the biological variations. Additionally, the haemostatic markers were not shown to have significant associations with thrombin generation, suggesting that the increased thrombin concentration during the luteal phase would be mediated by another mechanism, as yet unidentified. less thanbrgreater than less thanbrgreater thanThe associations between progesterone and the haemostatic markers, as shown for both phases of the menstrual cycle, suggest a previously unknown or undefined yet potentially significant role for progesterone in the coagulation system. However, it has been shown that the use of progestogen-only preparations does not affect the coagulation system, which is partly the reason why they are considered safe for women with thrombophilia or previous thrombotic event. Further studies are required in order to demonstrate whether our results can be extrapolated for synthetic progestins, which might have significant implication on the indications for their use. less thanbrgreater than less thanbrgreater thanThis study was supported by the Karolinska Institutet, Linkping University and the County Council of stergtland. The authors report no conflicts of interest.

Nyckelord

coagulation factors

thrombin generation

menstrual cycle

progesterone

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