Exploring predictive factors for spontaneous expulsion of retained products of conception.

INTRODUCTION: Retained products of conception (RPOC) are persistent placental tissues within the uterus after pregnancy, managed through expectant, pharmacological, or surgical approaches. Surgical treatment carries risks such as uterine perforation and adhesion formation. Predictors of spontaneous RPOC expulsion (SE) remain unclear. This exploratory study aimed to identify candidate predictors of successful expectant management. MATERIALS AND METHODS: This multicentre study combined data from a randomised trial and an observational cohort (2015-2022) in three Dutch hospitals and one Belgian university hospital. Women with ultrasonographically confirmed RPOC (1-4 cm) were included. Demographic, clinical, and ultrasound variables were prospectively collected. Variables with p < 0.15 in univariate analyses were entered into three multivariable analyses, using Firth's penalised logistic regression given the low event rate. RESULTS: Of 351 women with RPOC, 38 (10.8%) experienced SE. In the general analysis, a larger RPOC diameter was associated with a reduced likelihood of SE (OR 0.94; 95% CI 0.89-.99; p = 0.03). In first-trimester cases, absence of embryonic cardiac activity was associated with a higher likelihood of SE of RPOC (OR 3.7; 95% CI 1.2-13.8; p = 0.03). No significant predictors were found in third-trimester cases, though RPOC diameter showed a borderline association. CONCLUSION: Smaller RPOC diameter and absence of embryonic cardiac activity in first-trimester losses were associated with a higher likelihood of SE of RPOC. Given the exploratory design and limited number of events, these findings should be regarded as hypothesis-generating. Larger, prospective studies with standardised follow-up and well-defined patient subgroups are needed to confirm these candidate predictors and inform their potential clinical application.