Objective: To assess cabergoline's efficacy at decreasing breast symptoms after second-trimester abortion or pregnancy loss.

Methods: This was a double-blinded, block-randomized superiority trial comparing cabergoline 1 mg once to placebo for preventing bothersome breast engorgement after second-trimester uterine evacuation. We enrolled pregnant people at 18-28 weeks of gestation who were English- or Spanish-speaking and without contraindication to the study drug. Participants completed a validated, piloted, electronic survey at baseline and at multiple timepoints through 2 weeks postprocedure to assess breast symptoms, side effects, and bother. Our primary outcome was any breast symptoms (a composite of engorgement, milk leakage, tenderness, and need for pain relief) on day 4; we planned to enroll 80 patients to show a 30% difference in breast symptoms (80% power, α=0.049). A subgroup of participants returned for serum prolactin levels.

Results: After screening 150 patients from April 2021 to June 2022, we enrolled 73 participants. Baseline demographics were balanced between groups: median gestational age was 21 weeks (range 18-26 weeks), 56.2% of participants were nulliparous, 34.2% self-identified as Hispanic, and 37.0% had public insurance. At baseline, reported breast symptoms were similar between groups. Among 69 participants who returned surveys on day 4, significantly fewer participants receiving cabergoline reported any breast symptoms compared with placebo (27.8% vs 97.0%, P<.001) (primary outcome) and fewer reported significant bother (2.8% vs 33.3%, P=.001) (secondary outcome). These differences persisted through day 14. Reported incidence and severity of bother from side effects were similar between groups: most common were constipation, fatigue, and headache. Serum prolactin levels were similar at baseline. On day 4, mean serum prolactin level was 6.5 ng/mL (SD 2.2) for those who received cabergoline and 18.0 ng/mL (SD 5.9) for placebo (P=.049).

Conclusion: Cabergoline is an effective and well-tolerated strategy to prevent breast symptoms after second-trimester abortion or pregnancy loss.

Clinical trial registration: ClinicalTrials.gov, NCT04701333.