Evaluation of pregnancy-related cells in endometrial cytology.

Objective: To determine the significance of pregnancy-related cells in endometrial smears.
Study Design: Pregnancy-related cells in 4429 endometrial smear samples were retrospectively analyzed and evaluated for clinicopathologic and cytomorphologic features.
Results: Of the 4429 endometrial smears taken for cancer screening, pregnancy-related cells were detected in 12 cases (0.3%). They were estimated cytologically as negative or suspicious and confirmed as cases ofspontaneous abortion (8 cases), placental site nodule (3 cases), and partial hydatidiform mole (1 case). Decidual cells were observed in all cases, and some of these showed atypia. Trophoblasts were observed in 5 (41.7%) of the 12 cases. Syncytiotrophoblasts were observed in 1 case (8.3%) and nonsyncytiotrophoblasts in 5 (41.7%) of the 12 cases. Pregnancy-related cells were observed in an endometrial smear in 7 cases; other cases were missed during cytologic examination and were retrospectively identified.
Conclusion: Pregnancy-related cells are likely to be missed because they are difficult to identify or are surrounded by a cluster of endometrial cells. The decidual cell is a key cell for the cytologic diagnosis of pregnancy-related cells. Determining the existence of pregnancy-related cells in endometrial smears is important for the further assessment of patients and the differential diagnosis of several endometrial lesions.