Background: Recurrent implantation failure remains a challenge in assisted reproduction. Intralipid has been proposed as an immunomodulatory intervention to improve outcomes, although evidence remains inconsistent.

Objective: This study aimed to evaluate the effect of intralipid on pregnancy outcomes in women with a history of at least 2 failed embryo transfer cycles.

Materials and Methods: In this retrospective cohort study, data of 270 women with ≥ 2 failed embryo transfer cycles, who underwent a subsequent frozen embryo transfer (FET) at Avicenna Fertility Center, Tehran, Iran, from March 2021–2022 were extracted from medical records. Participants were allocated to the intralipid group (n = 132), receiving 100 mL intravenous intralipid 20% 1 wk before FET, if beta-human chorionic gonadotropin was positive, the same dose was given every 4 wk until the end of the first trimester, or to the control group (n = 138), undergoing routine FET treatments. Outcomes included biochemical, clinical, and ongoing pregnancy, abortion, and live birth.

Results: Biochemical pregnancy rate was significantly higher in the intralipid group compared with controls (51.5% vs. 37.7%, p = 0.022). Clinical pregnancy (43.2% vs. 36.2%), ongoing pregnancy (28.8% vs. 18.8%), and live birth (25.8% vs. 17.4%) also favored the intralipid group, although these differences did not reach statistical significance (p > 0.05). Abortion rates were comparable between groups (25.8% vs. 21.0%, p = 0.357).

Conclusion: Intralipid may improve biochemical pregnancy rates and shows a non-significant positive trend in other pregnancy outcomes in recurrent implantation failure cases, warranting confirmation in larger randomized controlled trials.

Keywords: Fat emulsions, Intravenous, Embryo implantation failure, Fertilization in vitro, Pregnancy outcome, Immunomodulation

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