What are the ultrasound and biochemical features of impending ovulation?

Thirty-two ovulatory women had serial ultrasound measurements of uterine volume, endometrial thickness and leading follicular diameter compared with serum oestradiol, testosterone and sex-hormone binding globulin. Follicular diameter, endometrial thickness and uterine volume were significantly correlated with serum oestradiol. The day before ovulation was characterized by maximal values for oestradiol, testosterone, luteinizing hormone, endometrial thickness, uterine volume and leading follicular diameter. Leading follicular diameter and endometrial thickness in particular, appear to be useful parameters to indicate impending ovulation.