Does endogenous sex hormone binding globulin influence the contraceptive effect of levonorgestrel?

On the basis of four previous clinical studies a direct relationship of the contraceptive effect of levonorgestrel expressed as a suppression of ovarian function) to individual levels of sex hormone binding globulin may be assumed. The rationale of this dependence seems to be the protection against metabolic degradation which is provided by sex hormone globulin to levonorgestrel.