Association between adenomyosis and late miscarriage: a retrospective cohort study

Background Adenomyosis is increasingly diagnosed in women of reproductive age due to advances in imaging and standardised criteria. Beyond its gynaecological symptoms, emerging evidence suggests associations with adverse obstetric outcomes. While associations with placental disorders including placenta praevia and placenta accreta spectrum (PAS) are often reported, the impact of adenomyosis on late miscarriage remains poorly defined. This study primarily evaluated the relationship between adenomyosis and late miscarriage, and secondarily other obstetric complications, especially placental disorders. Methods This single-centre retrospective cohort study included all singleton deliveries at OBGYN Department from CHU Liège – Citadelle Hospital (Belgium) between January 2020 and December 2023. Pregnancies with predefined complications were identified from institutional delivery registry and paired with temporally adjacent uncomplicated deliveries to construct an outcome-enriched cohort. Adenomyosis was diagnosed based on transvaginal ultrasonography (applying Morphological Uterus Sonographic Assessment (MUSA) criteria) and/or magnetic resonance imaging (MRI) reports, assessed up to six weeks postpartum. Multivariate logistic regression estimated the association between adenomyosis and late miscarriage, adjusted for endometriosis, mode of conception and congenital uterine malformations. Results A total of 2620 singleton deliveries were analysed, including 86 cases of adenomyosis (3.3%). Women with adenomyosis were older and more frequently conceived using assisted reproductive technologies. Adenomyosis was associated with higher odds of overall obstetric morbidity (OR 1.64, 95%CI: 1.06–2.55, p = 0.03). The odds of late miscarriage were significantly higher in adenomyosis group (OR 3.88, 95%CI: 1.62–9.34, p = 0.0077) and remained independently associated after adjustment (aOR 2.95, 95%CI: 1.04 − 7.15, p = 0.043). Adenomyosis was also associated with increased odds of PAS (OR 2.44, 95%CI: 1.15–5.20, p = 0.026) and placenta praevia (OR 3.48, 95%CI: 1.21–10.03, p = 0.037). Conclusions Adenomyosis was independently associated with late miscarriage in this cohort. Given that adenomyosis-related alterations, including ectopic endometrium within myometrium, chronic inflammation, impaired uterine contractility and abnormal vascular remodelling, may impair placental development, affected pregnancies may benefit from increased clinical awareness and careful antenatal surveillance, particularly during second trimester. Further prospective studies using pre-conception standardised imaging and detailed phenotyping are needed to clarify underlying mechanisms and optimise clinical management. Trial registration not applicable.