In people with infertility-related endometriosis, the risk for ankylosing spondylitis is high.

A study aimed to examine the potential causal link between different clinical forms of endometriosis and ankylosing spondylitis, employing Mendelian randomization (MR) analysis. MR was conducted using data sourced from genome-wide association studies (GWASs).

A range of analyses, such as assessing heterogeneity, pleiotropy, and conducting sensitivity analyses, were carried out to gauge the robustness of the results using MR Egger and inverse variance weighted (IVW) methods. Additionally, a leave-one-out analysis was performed. The investigation into the relationship between ankylosing spondylitis and endometriosis utilized weighted median, inverse variance weighted multiplicative random effects (IVW-MRE), IVW, and MR Egger approaches.

The IVW analysis indicated a causal relationship between infertility-associated endometriosis and ankylosing spondylitis (Odds Ratio [OR] = 0.8334). This same result was consistent with the IVW-MRE analysis (OR = 0.8334). However, when further analysis was conducted, stratifying the data, it became apparent that regardless of the statistical method used, there was no evidence of a causal relationship between endometriosis and ankylosing spondylitis for specific subtypes:

• Ovarian endometriosis (IVW: OR = 0.1662; IVW-MRE: OR = 0.1662; MR Egger: OR = -0.9577; Weighted median: OR = 0.2628).
• Pelvic peritoneum endometriosis (IVW: OR = 0.4363; IVW-MRE: OR = 0.4363; MR Egger: OR = 4.159; Weighted median: OR = 0.4112).
• Rectovaginal endometriosis (IVW: OR = 0.1365; IVW-MRE: OR = 0.1365).

Individuals diagnosed with infertility-related endometriosis faced a heightened risk of development of ankylosing spondylitis. Therefore, the research underscores the importance of healthcare providers being vigilant regarding the prevalence of ankylosing spondylitis in such people.