Association of unexplained recurrent implantation failure with obstetric and neonatal outcomes: cohort study of 37 888 singleton live births

Objective To investigate the risk of adverse obstetric and neonatal outcomes in patients with unexplained recurrent implantation failure (uRIF) who had a singleton live birth. Methods This multicenter retrospective cohort study reviewed 49 372 embryo‐transfer cycles leading to a singleton live birth at three fertility centers in China between January 2014 and July 2021. Patients were categorized into the uRIF group if they had a history of at least three failed transfers of unknown cause with at least four good‐quality embryos, while the control group comprised women who had experienced fewer than three failed implantation cycles. Obstetric and neonatal outcomes were collected via telephone interviews using a standardized questionnaire. Propensity score matching (PSM) and multivariate logistic regression analysis were used to control for potential confounders. Results After exclusions, 1244 patients with a history of uRIF and 36 644 controls were included in the study. All baseline characteristics were balanced following PSM, with 1243 patients retained in each group. Compared with the control group, the uRIF group exhibited significantly higher odds of placenta previa (2.7% vs 1.4%; adjusted odds ratio (aOR), 2.01 (95% CI, 1.01–4.00)), placental abruption (0.3% vs 0%; aOR, 6.51 (95% CI, 1.57–26.91)), Cesarean delivery (76.6% vs 71.8%; aOR, 1.27 (95% CI, 1.06–1.53)) and preterm birth (10.1% vs 7.3%; aOR, 1.44 (95% CI, 1.08–1.91)). The results remained consistent on sensitivity analysis using prematched data with multivariate adjustment. Conclusions A history of uRIF was associated with increased risks for placenta previa, placental abruption, Cesarean delivery and preterm birth. While statistically significant, the absolute differences in the rates of these complications were modest and the clinical relevance of our findings should be interpreted with caution.