Pharmacokinetics and ovarian suppression during use of a contraceptive vaginal ring in normal-weight and obese women
American Journal of Obstetrics and Gynecology, 05/01/2012  Clinical Article

Westhoff CL et al. – While obese women had lower EE levels during CVR use, they had excellent suppression of ovarian follicle development, similar to normal weight women. This predicts that CVR effectiveness will be similar in women with a BMI up to 39.9. The lower serum EE levels in the obese women may explain the greater reported bleeding or spotting days.

• 20 normal weight (BMI 19.0–24.9, median 21.65) and 20 obese (BMI 30.0–39.9, median 33.7) women enrolled in a prospective study of ethinyl estradiol (EE) and etonorgestrel (ENG) pharmacokinetics and of ovarian follicle development, endometrial thickness, and bleeding patterns, all measured biweekly during the second cycle of CVR use.

• Thirty–seven women completed follow–up.
• Mean day 0–21 EE concentrations were lower among obese versus normal weight women (15.0 versus 22.0 pg/mL, respectively. p = 0.004), while ENG concentrations were similar (1138 versus 1256 pg/mL, respectively. p = 0.39).
• Follicular development was minimal in both groups, with only five women achieving a maximum follicle diameter > 13mm at any time during 3 weeks follow–up (3 normal weight and 2 obese women); these women had serum progesterone levels < 1.0.
• Obese women reported more bleeding or spotting than normal weight women (3.6 versus 1.4 days, respectively. p = 0.01).