How does endometriosis impact embryo transfer success rates?

Highlights

• Endometriosis is broadly considered to negatively impact embryo transfer success by reducing the likelihood of implantation and subsequent live birth.
• The condition may reduce a patient's chance of a live birth from a single transfer from 50% down to 40-45%.
• Beyond implantation, endometriosis is a risk factor for the entire pregnancy, increasing rates of early loss and later obstetrical complications.
• When reviewing studies, it is critical to confirm if they used euploid embryos, as this is a major confounding variable.
• Research is challenging because endometriosis varies greatly in its location, severity, and subtype, which all affect fertility outcomes differently.

Article

The Deleterious Effect of Endometriosis on Embryo Transfer

While the precise mechanisms remain an area of active investigation, a consensus exists among experts that endometriosis negatively impacts embryo transfer success rates. Dr. Amanda Adeleye notes the established clinical observation that patients with endometriosis "tend to do slightly worse" in IVF compared to those with other causes of infertility. Dr. Joseph Letourneau provides a quantitative estimate of this effect, suggesting that a patient with a baseline 50% chance of live birth from an embryo transfer might see that probability decrease to 40% or 45% in the context of endometriosis. While not an absolute barrier, the condition presents an additional challenge. Dr. Antonio Gargiulo offers a more definitive stance, stating that the impact is "always a deleterious, so a negative, factor" on reproductive success.

The Challenge of Disease Phenotype

A primary difficulty in studying and managing endometriosis-related infertility is the heterogeneity of the disease. Dr. Letourneau emphasizes that phenotyping is a significant challenge, as the condition can manifest differently in each patient. He argues that the impact on fertility likely varies depending on the location and volume of the disease, distinguishing between endometriosis on the pelvic sidewalls, involvement of the fallopian tubes, or its presence within the uterine muscle, a condition known as adenomyosis. This clinical variability complicates research and makes it difficult to predict outcomes in any single case. Dr. Adeleye concurs that while the association is known, it is "hard to say exactly why in every endometriosis circumstance."

Impact Beyond Implantation: A Full-Term Perspective

The negative influence of endometriosis may extend far beyond the initial phase of implantation. Dr. Letourneau theorizes that the endometrium itself might be "abnormal to begin with," and the properties that allow it to grow ectopically may inherently interfere with the complex process of embryo implantation. Expanding on this, Dr. Gargiulo warns that the disease is problematic throughout gestation. He urges clinicians to look beyond simple pregnancy rates and focus on the "baby home" rate, citing increased risks of early pregnancy loss and other obstetrical complications in patients with endometriosis. He describes the condition as a "danger for reproductive success from beginning to end of the pregnancy process," highlighting its role as a high-risk factor through to delivery.

"Nobody cares about the pregnancy rate. What you care about is the rate of baby home." Dr. Antonio Gargiulo

Critically Appraising the Evidence

When evaluating the literature, Dr. Gargiulo provides a critical framework for physicians. He cautions that a majority of historical IVF studies may be of "limited use" due to a significant confounder: embryo aneuploidy. He asserts that for a study on this topic to be valid, it must use chromosomally normal (euploid) embryos, typically confirmed via preimplantation genetic testing (PGT). Without this control, any observed difference in outcomes could simply be due to one group having more euploid embryos by chance, rather than the effects of endometriosis. This insight is crucial for interpreting conflicting study results and applying evidence to clinical practice.

"The majority of fertility studies that have been done before pre-implantation genetics were of limited use." Dr. Antonio Gargiulo

Clinical Management and Future Directions

Despite the challenges, clinicians can maintain a hopeful outlook for their patients. As Dr. Letourneau notes, many individuals with endometriosis achieve successful pregnancies, whether through IVF or other means. The key is recognizing that the path may be "a little bit more challenging." The future of treatment is focused on mitigating the disease's impact on the uterine environment. Dr. Letourneau expresses optimism for research over the next five to ten years, anticipating the development of strategies to "normalize the endometrium" or reduce inflammation, thereby improving implantation and pregnancy rates for this patient population.