How does endometriosis impact embryo transfer success rates?

Highlights

• Experts agree that endometriosis can negatively affect embryo transfer success, modestly reducing implantation and subsequent live birth rates compared to other infertility conditions.
• The impact of endometriosis is hard to study due to phenotypic variation in disease location and severity, which can progress over time.
• Quantitatively, known endometriosis may reduce the chance of live birth from a given embryo transfer from 50% down to approximately 40-45%.
• Beyond implantation, endometriosis is also associated with higher rates of early pregnancy loss and an increased risk of obstetrical complications through delivery.
• When reviewing literature, studies that do not exclusively use euploid embryos may be of limited value due to confounding chromosomal abnormalities.

Expert Insights

The Impact of Endometriosis on Embryo Transfer Success

Experts concur that endometriosis can negatively impact the success rates of embryo transfer, though the precise mechanisms and magnitude of this effect remain subjects of ongoing investigation. Dr. Amanda Adeleye notes that patients with endometriosis who undergo IVF tend to have slightly lower success rates compared to those with other causes of infertility. This general consensus is complicated by significant clinical and research challenges. As Dr. Joseph Letourneau explains, one of the primary difficulties is the heterogeneity of the disease itself.

The Critical Role of Disease Phenotype

The clinical impact of endometriosis on fertility is not uniform and likely depends on the specific presentation of the disease. Dr. Letourneau emphasizes the challenge of phenotyping, noting that the condition manifests differently among patients. For example, disease located on the pelvic sidewalls may have a different impact than disease involving the fallopian tubes or the uterine muscle—a continuum known as adenomyosis. The location, extent, and progression of the disease are all critical variables. "As researchers, we ask whether all endometriosis is bad for fertility," Dr. Letourneau states. "It's probable that some forms affect fertility more than others." This variability makes it difficult to predict outcomes for an individual patient and complicates research efforts aiming to establish a definitive link between endometriosis and implantation failure.

"It's probable that some forms affect fertility more than others." Dr. Joseph Letourneau

Quantifying the Effect on Implantation

While a precise figure is elusive, the effect of endometriosis on implantation is generally considered to be a modest reduction rather than an absolute barrier. Dr. Letourneau offers a clinical estimate: if a given euploid embryo transfer has a 50% chance of resulting in a live birth, the presence of known endometriosis might reduce that chance to approximately 40–45%. He frames this within the broader context of human reproduction's relative inefficiency, suggesting that while many patients with endometriosis do conceive, it may require more time or additional attempts. A patient with endometriosis might need a somewhat longer time to conceive compared to a patient without the condition.

Methodological Hurdles and Risks Beyond Implantation

The scientific literature on this topic presents a mixed picture, which Dr. Antonio Gargiulo attributes to methodological challenges in study design. He cautions clinicians to critically evaluate IVF studies, particularly older research conducted before the widespread use of preimplantation genetic testing for aneuploidy (PGT-A). "When reading IVF studies, first ask whether they used euploid embryos," he advises, explaining that results may be confounded by chromosomal abnormalities if this variable is not controlled.

Dr. Gargiulo asserts that well-designed studies do show that endometriosis is a "deleterious factor for reproductive success from conception to delivery." Its impact extends beyond implantation, as the condition is associated with higher rates of early pregnancy loss. Furthermore, he notes that endometriosis remains a risk factor throughout gestation, contributing to a higher incidence of obstetrical complications compared to the general population.

"Endometriosis is a deleterious factor for reproductive success from conception to delivery." Dr. Antonio Gargiulo

Potential Mechanisms and Future Directions

The underlying pathophysiology linking endometriosis to reduced implantation rates is thought to involve endometrial receptivity. Dr. Letourneau posits that an endometrium capable of ectopic implantation may be inherently abnormal. These same properties, he suggests, could impair its ability to support the complex process of embryo implantation within the uterus. Looking ahead, he expresses optimism that research over the next five to ten years will clarify whether interventions aimed at normalizing the endometrium or reducing inflammation can help improve and maintain high pregnancy rates for this patient population.