{"paper_id":"d39bf0c8-4412-4235-b1ee-f7ef6b1e7019","body_text":"Abstract\nBackground\nThe 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.\nMethods\nA 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.\nResults\nFor 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).\nConclusions\nUltrasound-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.\nSimilar content being viewed by others\nAbbreviations\n- ART:\n-\nAssisted reproductive technology\n- FET:\n-\nFrozen embryo transfer\n- MUSA:\n-\nThe international Morphological Uterus Sonographic Assessment\n- FAOM:\n-\nFocal adenomyosis of the outer myometrium\n- GnRHa:\n-\nGonadotropin-releasing hormone agonist\n- JZ:\n-\nJunctional zone\n- PGT:\n-\nPreimplantation genetic testing\n- 2D:\n-\nTwo-dimensional\n- 3D:\n-\nThree-dimensional\n- BMI:\n-\nBody mass index\n- SD:\n-\nStandard deviation\n- AFC:\n-\nAntral follicle count\n- CYP-19:\n-\nCytochrome P450 Family 19\n- CLBR:\n-\ncumulative live birth rate\nAcknowledgements\nNot applicable.\nFunding\nThis work was supported by the National Natural Science Foundation of China (No. 82071646, 82371678), Scientific research project of Jiangsu Province Association of Maternal and Child Health (No. FYX202203), Open project of the Affiliated Jiangning Hospital of Nanjing Medical University Immune Cell Transformation Research Center (JNYYZXKY202213), Nanjing Drum Tower Hospital Medical Center Project (2022-YXZX-FC-03), Fertility Research Program of Young and Middle-aged Physicians-Clinical Research In 2022 (Beijing Health Promotion Association, BJHPA-2022-SHZHYXZHQNYJ-LCH-002). There are no conflicts of interest.\nAuthor information\nAuthors and Affiliations\nCorresponding authors\nEthics declarations\nEthics approval and consent to participate\nThis retrospective study received ethical approval from the ethics committee of Nanjing Drum Tower Hospital. All methods followed the relevant guidelines and regulations, strictly adhering to the Declaration of Helsinki. The informed consent was waived by the same ethics committee that approved the study (the ethics committee of Nanjing Drum Tower Hospital).\nConsent for publication\nNot applicable.\nCompeting interests\nThe authors declare no competing interests.\nAdditional information\nPublisher’s Note\nSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.\nSupplementary Information\nRights and permissions\nOpen Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.\nAbout this article\nCite this article\nJiang, J., Li, L., Hou, X. et al. 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. BMC Pregnancy Childbirth (2026). https://doi.org/10.1186/s12884-026-09624-x\nReceived:\nAccepted:\nPublished:\nDOI: https://doi.org/10.1186/s12884-026-09624-x","source_license":"public-domain-us","license_restricted":false}