The Immune Cells That Could Predict IVF Success—What Doctors Are Learning

When couples undergo in vitro fertilization (IVF), the moment an embryo is transferred into the uterus is filled with hope and uncertainty. Now, researchers at the University of Miami are discovering that the immune environment inside the uterus during embryo transfer may hold clues about whether pregnancy will succeed. A groundbreaking study suggests that measuring certain immune cells at the time of transfer could help predict live birth outcomes.

What Immune Cells Matter Most During Embryo Transfer?

Scientists examined immune cells collected from 48 people undergoing frozen embryo transfer (FET)—a procedure where a previously frozen embryo is thawed and placed into the uterus. The research team, led by investigators in the Department of Obstetrics, Gynecology and Reproductive Sciences at the University of Miami Miller School of Medicine, analyzed the types and quantities of immune cells present in the uterus at the moment of transfer.

The findings revealed two critical immune cell types that appear to influence implantation success:

• Gamma-delta T cells (γδ T cells): These specialized immune cells were significantly higher in people who achieved live birth compared to those whose embryos failed to implant, with a statistical difference that researchers found meaningful.
• Neutrophils (CD66b+ cells): These infection-fighting white blood cells were elevated in people who experienced implantation failure, suggesting their presence may interfere with successful pregnancy establishment.
• Other immune markers: Researchers also measured CD3, CD19, CD4, CD8, CD25, CD127, CD14, and CD56 cells to create a complete picture of the uterine immune environment.

How Accurate Can These Immune Markers Predict Pregnancy Success?

The study results were encouraging. Among the 48 participants, 24 achieved live birth (50%), four experienced miscarriages (8.3%), and three had biochemical pregnancies—pregnancies detected only by hormone levels but not by ultrasound (6.3%).

When researchers used statistical analysis to test whether immune cell measurements could distinguish between successful and unsuccessful outcomes, gamma-delta T cells showed a predictive accuracy of 72%, while neutrophils demonstrated 75% accuracy. These results suggest that immune cell profiling could become a practical tool for identifying which patients have the most favorable uterine environment for implantation.

Why Does the Uterine Immune Environment Matter?

The uterus is not an immune-neutral space. It contains a carefully balanced collection of immune cells that must work together to allow an embryo to implant while still protecting against infection. This delicate balance is called "endometrial receptivity"—essentially, the uterus's readiness to accept and nurture an embryo.

Previous research has focused on cytokines—chemical messengers that immune cells use to communicate—but specific information about which immune cell types are present during the critical window of embryo transfer has been limited. This study fills that gap by directly measuring immune cells collected from the transfer catheter immediately after the procedure.

The research team explained that understanding these immune profiles could transform how fertility specialists approach treatment. By identifying patients with less favorable immune environments, doctors might eventually develop interventions to optimize the uterine immune landscape before transfer, potentially improving success rates for those who struggle with implantation failure.

What's Next for Fertility Treatment?

While these findings are promising, the researchers emphasize that this is exploratory work. The study included 48 participants, which is relatively small, and the results need confirmation in larger populations before immune cell profiling becomes standard clinical practice.

However, the potential applications are significant. If validated, immune cell profiling could help fertility specialists identify which patients might benefit from immune-modulating treatments, personalize transfer timing, or adjust hormone protocols to create a more receptive uterine environment. For people who have experienced repeated implantation failures, this type of testing could provide answers about why their bodies are rejecting embryos and offer a path toward successful pregnancy.

The study represents one of the first efforts to directly link immune cell profiles measured during the actual embryo transfer cycle with IVF outcomes, opening a new frontier in understanding why some embryos thrive while others fail to implant.