Association between CD138-positive cell count in endometrial stroma and pregnancy outcomes after single blastocyst transfer.

The impact of endometrial CD138-positive cell numbers on pregnancy outcomes in chronic endometritis (CE) remains uncertain. This study examined the association between CD138-positive cell counts in endometrial stroma and pregnancy results following frozen-thawed single blastocyst transfer (SBT) cycles. Approved by the institutional Ethics Committee, this retrospective case-control study included 166 infertile women under 40 years old who underwent frozen-thawed SBT with morphologically and developmentally good-quality blastocysts within 3 months of an endometrial biopsy for CD138 immunostaining between September 2020 and August 2021. Endometrial stromal CD138-positive cells were counted in 10 high-power fields (HPFs). Pregnancy outcomes were compared among groups with 0, 1-4, and ≥ 5 CD138-positive cells, comprising 71, 72, and 20 patients, respectively. Prior antibiotic treatment rates for CE were 53.5 %, 52.8 %, and 100 % in the 0, 1-4, and ≥ 5 cell groups, respectively (p < 0.001). The clinical pregnancy rates after SBT were 60.6 % (43/71), 66.7 % (48/72), and 35.0 % (7/20) for the respective groups, with lower rates in women with ≥ 5 positive cells compared to those with 0-4 (odds ratio: 0.31, 95 % confidence interval: 0.12-0.82, p = 0.02). Miscarriage rates did not differ significantly among the groups (25.6 %, 20.1 %, and 28.6 %; p = 0.81). The presence of five or more CD138-positive cells per 10 HPFs negatively affected pregnancy success after SBT, whereas patients with 1-4 positive cells may not require antibiotic treatment.