<p>This retrospective cohort study evaluated whether gonadotropin-releasing hormone agonists (GnRHa) used for luteal support during antagonist cycles improved pregnancy outcomes in patients undergoing fresh embryo transfer. We examined 3,115 patients who underwent antagonist-protocol in vitro fertilization and embryo transfers between February 2022 and December 2023. We compared a group that received luteal support with GnRHa (<i>n</i> = 262) with a conventional support group (<i>n</i> = 2,853). Prior to propensity score matching (PSM), the GnRHa group demonstrated a significantly higher clinical pregnancy rate (59.54%) than the conventional group (53.80%; <i>p</i> = 0.042); this rate remained significant after PSM (<i>p</i> = 0.026). The GnRHa group with progesterone levels &lt; 1.0 ng/ml on the day of administration exhibited significantly higher clinical pregnancy rates than the conventional group (64.88% vs. 53.73%, respectively; <i>p</i> = 0.020). Similarly, patients undergoing fresh single blastocyst transfer who received GnRHa demonstrated significantly higher clinical pregnancy, implantation, and live birth rates (67.57%, 56.76%, and 48.65%, respectively) than those in the conventional group (<i>p</i> = 0.003 0.024, and 0.036, respectively). The results of this study showed that the introduction of GnRHa during fresh embryo transfer for patients undergoing antagonist cycles strengthened luteal support and improved clinical pregnancy rates.</p>