RESUMEN
OBJECTIVE: A controversy persists over whether or not the type of embryo transfer (ET) influences reproductive outcomes. This study aimed to evaluate the reproductive outcomes of pregnant patients undergoing their first in vitro fertilization procedure and explore the influence of various KIR genotypes on these reproductive outcomes. PATIENTS AND METHODS: Prospective enrollment of patients with infertility who sought treatment at Origyn Fertility Center in Iasi, Romania, was conducted between January 2019 and March 2023. Descriptive statistics and average treatment effects (ATE) using propensity-score matching were employed to analyze our data. RESULTS: Our results indicated that both groups were homogenous regarding baseline characteristics. When we evaluated the ATE of fresh vs. frozen ET on the main outcomes, we discovered that only frozen ET significantly improved the pregnancy rates (ATE: 0.17, 95% CI: 0.04-0.30, p=0.011) and live birth rates (ATE: 0.36, 95% CI: 0.02-1.19, p=0.03). The miscarriage rates were similar between the two groups. None of the evaluated KIR genotypes had a significant influence on the ATE corresponding to fresh and frozen ET. CONCLUSIONS: KIR screening is not necessary before an IVF cycle, except for specific situations such as recurrent pregnancy loss or recurrent implantation failure.