Clinical features and reproductive outcomes after first frozen embryo transfer in patients with different ultrasound-diagnosed adenomyosis subtypes following ultralong gonadotropin-releasing hormone agonist pretreatment: a retrospective cohort study

BACKGROUND: The differences between adenomyosis subtypes in clinical features and reproductive outcomes remain largely unexplored. This study aimed to compare clinical features and reproductive outcomes after the first frozen embryo transfer (FET) among patients with different ultrasound-diagnosed adenomyosis subtypes following ultralong gonadotropin-releasing hormone agonist (GnRHa) pretreatment. METHODS: A retrospective cohort study was conducted and included infertility patients with (n = 179) and without (n = 179) adenomyosis undergoing first FET. Patients with adenomyosis underwent the ultralong GnRHa pretreatment before their first FET cycle. Adenomyosis was diagnosed by two-dimensional (2D) and three-dimensional (3D) transvaginal sonography (TVS) and classified into subtypes according to types (diffuse/focal/mixed) and locations (inner/outer myometrium) of lesions. Baseline characteristics, sonographic features and pregnancy outcomes after the first FET cycle were collected. The primary outcome was live birth rate after the first FET cycle. Secondary outcomes included implantation rate, clinical pregnancy rate, and miscarriage rate. RESULTS: For different subtypes of adenomyosis, patients with internal adenomyosis had a significantly higher incidence of secondary infertility than those with external adenomyosis (70.0% vs. 47.0%, P = 0.006). Patients with external adenomyosis had higher incidence of coexisting ovarian endometriosis than internal adenomyosis (27.3% vs. 13.6%, P = 0.029). Patients with diffuse and internal adenomyosis exhibited significantly larger uterine sizes and thicker anterior walls compared to those with focal (180.57 ± 33.90 mm vs. 164.32 ± 25.12 mm, P = 0.026; 21.86 ± 8.35 mm vs. 18.54 ± 7.25 mm, P = 0.042) and external adenomyosis (183.73 ± 33.56 mm vs. 165.95 ± 28.44 mm, P < 0.001; 22.92 ± 8.47 mm vs. 18.13 ± 6.81 mm, P < 0.001), respectively. No statistically significant differences were found between infertility patients with adenomyosis and without adenomyosis in baseline characteristics. Patients with adenomyosis had a lower implantation rate than those without adenomyosis (50.7% vs. 62.8%, P = 0.010), whereas live birth rate after the first FET cycle did not differ significantly between groups (49.2% vs. 47.5%, P = 0.833). In adenomyosis patients, multivariable logistic regression showed that greater reduction in junctional zone thickness after treatment was associated with a lower risk of failure to achieve live birth after the first FET cycle (OR = 0.694; 95% CI: 0.502-0.961; P = 0.028). Endometrial thickness was independently associated with failure to achieve implantation after the first FET cycle (OR = 1.257; 95% CI: 1.039-1.521; P = 0.018). CONCLUSIONS: Ultrasound-based adenomyosis subtyping revealed distinct clinical profiles. Although live birth rate after the first FET cycle did not differ significantly between groups, adenomyosis was associated with reduced implantation rate. Exploratory regression analyses suggested that greater JZ thickness reduction indicated a favorable effect on live birth, and increased endometrial thickness may be associated with implantation failure. These findings should be interpreted cautiously because of the retrospective design and limited power of subgroup analyses.