P059Pharmacodynamic evaluation of the etonogestrel contraceptive implant initiated midcycle with and without ulipristal acetate: A pilot randomized controlled trial

Abstract

<h3>Objectives</h3> To determine the incidence of ovulation within five days of etonogestrel (ENG) implant insertion in the presence of a dominant follicle with and without same-day oral ulipristal acetate (UPA) administration. <h3>Methods</h3> This single site trial recruited people aged 18–35 with regular menstrual cycles and interest in an ENG implant without pregnancy risk. We initiated transvaginal ultrasounds on day 7–9 of menses and randomized participants 1:1 to ENG implant alone or with concurrent oral UPA when a dominant follicle reached ≥14 mm in diameter. We completed daily transvaginal ultrasounds and serum hormone levels for up to seven days post-insertion or transitioned to labs alone if we observed follicular collapse on ultrasound prior to the end of seven days. We defined ovulation as follicular rupture followed by a progesterone level ≥3ng/mL. <h3>Results</h3> We enrolled 35 people: 17 with ENG implant alone (mean enrollment follicular size: 15.2 mm ± 0.9 mm) and 18 with ENG implant and UPA (mean enrollment follicular size: 15.4 mm ± 1.2 mm, p=0.6). Ovulation occurred in 35.3% (n=6) of ENG implant–alone participants and in 61.1% (n=11) of ENG implant and were given UPA(Risk ratio (RR), 0.6; 95% CI, 0.3–1.2; p=0.1). <h3>Conclusions</h3> Although not powered to detect statistically significant differences, mid-cycle ovulation suppression was more common when the ENG implant was inserted alone than with same-day UPA administration, supporting concerns for drug-drug interactions between oral UPA and ENG. Ovulation suppression with the implant exceeds prior reports of oral levonorgestrel. Thus, the ENG implant is worth testing as emergency contraception.