The objective of this study was to examine the rate of ovulatory disruption when intramuscular depot medroxyprogesterone acetate (DMPA) is administered across graded stages of dominant follicle development.
DMPA was administered to healthy, ovulatory women, ages 18-33 years, upon reaching one of three randomly, pre-assigned dominant follicle sizes: 12-14mm, 15-17mm, and ≥18mm. Dominant follicles were followed via serial transvaginal ultrasound (TVUS) until reaching their assigned size for DMPA administration. Participants returned for five consecutive days thereafter to provide serum ovulation markers and undergo daily TVUS for follicle rupture. During the following two weeks, serum progesterone levels were drawn twice weekly to detect possible ovulatory delay or dysfunction. Serum medroxyprogesterone acetate (MPA) levels at 1 and 24 hours after DMPA administration were examined against ovulatory outcomes.  Twenty-six of 29 of enrolled women completed the study, 35% (9/26) of whom experienced follicle rupture. In one case of follicle rupture, ovulation could not be confirmed via serum markers. Larger follicles were more likely to rupture despite DMPA (12-14mm: 0%, 0/10; 15-17mm: 30%, 3/10; >18mm: 100%, 6/6;