Systemic complement C3 reduction in infertile women with endometrial dysbiosis: preliminary observations.

CONTEXT: Endometrial dysbiosis has been linked to infertility, but its relationship with systemic immune activity remains unclear.

AIMS: To examine whether endometrial microbiota phenotype is associated with serum complement profiles in infertile women.

METHODS

We enrolled 105 infertile women and classified endometrial microbiota by 16S rRNA gene sequencing as Lactobacillus-dominant microbiota (LDM) or non-LDM (NLDM). Complement data were available in 27 women: after excluding cases with missing C-reactive protein (CRP; n = 2) or CRP above the 95th percentile (n = 2), 23 women were analyzed for C3/C4 and 19 for CH50. Group comparisons used Welch's t-test and Fisher's exact test.

KEY

RESULTS

NLDM was associated with lower serum C3 than LDM (101.5 ± 12.4 vs 121.0 ± 18.0 mg/dL; P = 0.006). C4 and CH50 did not differ significantly between groups.

CONCLUSIONS

Endometrial dysbiosis was associated with selective C3 reduction in this infertile cohort, consistent with mild complement consumption.

IMPLICATIONS: Serum C3, interpreted with microbiota profiling, may provide a practical adjunct marker of inflammation-related infertility in routine care. Larger prospective studies are needed to validate these preliminary findings.