Transvaginal Ultrasonographic Characteristics of Different Types of Residual Pregnancy Tissue in Patients with Incomplete Medication Abortion

Objective This retrospective study aimed to investigate the transvaginal ultrasound (TVUS) characteristics of different pathological types of retained products of conception (RPOC)—chorionic-decidual versus non-chorionic-decidual—following incomplete medication abortion, to provide an imaging basis for individualized clinical management. Methods A total of 300 patients with incomplete medication abortion treated at Kunshan Traditional Chinese Medicine Hospital between January 2023 and June 2025 were enrolled. Based on histopathological examination, patients were categorized into a chorionic-decidual group (n = 214) and a non-chorionic-decidual group (n = 86). All patients underwent TVUS examination, which assessed uterine volume, residual tissue morphology (mass-like vs. patchy), echogenicity pattern (hyperechoic, hypoechoic, mixed), local blood flow distribution (graded by the Alder classification), and hemodynamic parameters (pulsatility index, PI; resistance index, RI). Differences in sonographic features between the two groups were statistically compared. Results The proportion of patients with increased uterine volume was significantly higher in the chorionic-decidual group than in the non-chorionic-decidual group (33.18% vs. 8.14%, P = 0.003). Residual tissue in the chorionic-decidual group predominantly presented as mass-like (80.84%), whereas in the non-chorionic-decidual group, it was mainly patchy (87.21%), with a significant intergroup difference (P < 0.001). Echogenicity in the chorionic-decidual group was primarily hypoechoic (28.97%) or mixed (55.61%), while the non-chorionic-decidual group showed predominantly hyperechoic signals (74.42%) (P < 0.001). Residual tissue in the chorionic-decidual group demonstrated significantly richer blood flow (Alder grades II-III: 89.72% vs. 10.47%, P < 0.001) and lower hemodynamic indices (PI: 0.87 ± 0.14 vs. 1.49 ± 0.20; RI: 0.62 ± 0.08 vs. 0.75 ± 0.12; both P < 0.001) compared to the non-chorionic-decidual group. Conclusions Chorionic-decidual RPOC is characterized on TVUS by vascular, mass-like lesions with hypoechoic/mixed echogenicity and low-resistance blood flow. In contrast, non-chorionic-decidual RPOC typically appears as avascular, patchy, hyperechoic foci with high-resistance flow. These distinct sonographic patterns allow for non-invasive preoperative differentiation of RPOC type, facilitating risk stratification for more personalized and precise patient care.