Matched-pairs analysis of ovarian suppression during oral vs. vaginal hormonal contraceptive use

This study was conducted to compare ovarian suppression during oral vs. vaginal hormonal contraceptive use. Secondary aims included comparison of endometrial thickness and bleeding patterns.

In two open-label trials assessing ovarian suppression, 33 compliant women completed both studies. They first used oral contraceptive pills (OCs) [randomized to either 20 mcg ethinyl estradiol (EE)/100 mcg levonorgestrel (LNG) or 30 mcg EE/150 mcg LNG] and subsequently used contraceptive vaginal rings (CVRs) (daily release of 15 mcg EE/120 mcg etonogestrel), all 21/7-day regimens. Participants had at least one run-in cycle using each contraceptive method prior to evaluation. During one cycle of each method, women underwent biweekly transvaginal sonography to measure ovarian follicular diameters and endometrial thickness. We also noted presence of a corpus luteum or a ruptured follicle as a marker of ovulation. Participants recorded bleeding days on paper calendars. We used matched-pairs analyses as appropriate.

During follow-up, we identified at least one ovarian follicle ≥8 mm in 20/33 (61%) OC users and 12/33 (36%) CVR users (matched-pairs analysis, p=.02). Similar trends were seen for larger follicles; however, we had limited statistical power to evaluate these differences. Median follicular diameter among OC users was larger than median follicular diameter among CVR users (p=.01). We did not observe a corpus luteum or ruptured follicle in any participant during either study. Endometrial thickness was similar during OC and CVR use (mean 4.1±1.4 vs. 4.1±1.6 mm, p=.9), as was the number of bleeding or spotting days (mean 2.1±2.4 vs. 1.9±2.1, p=.8). Oral contraceptive pill dose was unrelated to follicle diameter, endometrial thickness or bleeding.

Ovarian follicles ≥8 mm were more common in 33 compliant women during OC use than during CVR use, indicating that CVR use results in greater ovarian suppression than OC use.