AbstractThe effectiveness of intravenous immunoglobulin (IVIg) for patients with unexplained recurrent implantation failure (uRIF) remains debated. The objective of this study was to evaluate outcomes in patients with uRIF treated with intravenous immunoglobulin (IVIg) compared to a separate cohort of uRIF patients not receiving IVIg within our center. We performed a retrospective cohort study defining uRIF as \(\ge\) 3 unexplained previously failed high quality blastocyst transfer failures in patients with a body mass index < 35, aged < 42, non-smoking, with >7mm type I endometrium at time of transfers. Primary outcomes included live birth, miscarriage, or transfer failure. We documented IVIg side effects and maternal/fetal outcomes. Logistic regression analysis was used to assess for association of IVIg exposure with outcomes and adjust for confounders. The study included 143 patients, with a 2:1 ratio of controls to patients receiving IVIg treatment. The baseline characteristics were similar between groups. There was higher live birth rate (LBR) in patients receiving IVIg (32/49; 65.3%) compared to controls (32/94; 34%); p < 0.001). When stratifying patients into moderate and severe uRIF (respectively 3–4 and \(\ge\) 5 previous good quality blastocyst transfer failures), only patients with severe uRIF benefited from IVIg (LBR (20/29 (69%) versus 5/25 (20%) for controls, p = 0.0004). In the logistic regression analysis, IVIg was associated with a higher odds of live birth (OR 3.64; 95% CI: 1.78–7.67; p = 0.0004). There were no serious adverse events with IVIg. In conclusion, it is reasonable to consider IVIg in well selected patients with \(\ge\) 5 previous unexplained, high quality blastocyst transfer failures. A well-designed randomized controlled trial is needed to confirm these findings.