Deeper Trophoblastic Invasion and More-Promotive Vascular Remodeling in Tubal Isthmic Pregnancy Compared with Ampullary Pregnancy: A Retrospective Clinicopathological Study.

To explore clinical and pathological characteristics of tubal isthmic pregnancy. A single-center, retrospective clinicopathological cohort study was conducted in women diagnosed with tubal pregnancy that underwent salpingectomy in International Peace Maternal and Child Health Care Hospital from January 2018 to April 2023. A total of 598 eligible women with tubal pregnancy were included in the analysis, including 75 women with isthmic pregnancy and 523 women with ampullary pregnancy. Among women with isthmic pregnancy, 29 (38.67%) had trophoblastic infiltration into the muscular layer, while 46 (61.33%) had infiltration into the serosal layer. Meanwhile 66 (12.62%) women, 258 (49.33%) women, and 199 (38.05%) women had trophoblastic infiltration into the mucosal layer, muscular layer, and serosal layer of the ampullary pregnancy, respectively. The study found that women with isthmic pregnancy had enhanced trophoblastic activity, deeper vascular remodeling, increased trophoblastic infiltration into the deep wall of the tube, higher serum beta subunit of human chorionic gonadotropin (β-hCG) levels, and a higher probability of clinical manifestations. Additionally compared with ampullary pregnancy, the occurrence of isthmic pregnancy was positively correlated with salpingitis isthmica nodosa (AOR = 3.62, 95% CI 1.45-9.00, P < 0.01), and negatively correlated with the presence of chronic tubal inflammation (AOR = 0.24, 95% CI 0.09-0.64, P < 0.01). Salpingitis isthmica nodosa, not chronic inflammation of the fallopian tubes, may be a risk factor for isthmic pregnancy. Compared to ampullary pregnancy, isthmic pregnancy exhibits a more profound trophoblastic vascular remodeling of the fallopian tube and a greater tendency to infiltrate the deep layers of the tubal wall. These characteristics render it more concealed and perilous, underscoring the importance of early recognition and diagnosis.