Detection of fetal cells from transcervical mucus plug before first-trimester termination of pregnancy by cytokeratin-7 immunohistochemistry

Aim: The presence of fetal cells in the endocervical mucus of pregnant women was first reported in 1971. The uterine cavity is patent during the first trimester prior to fusion of amnion and chorion. Fetal cells from degenerating chorion frondosum are theoretically shed into the uterine cavity between seven and 13 weeks' gestation and are trapped in the transcervical mucus; they can be identified by immunohistochemistry. Method: Ninety-nine transcervical mucosal plugs from pregnant women of between 7 and 13 weeks before abortion were collected, fixed, embedded, sectioned and stained with monoclonal antibody of cytokeratin-7 (CK-7) by immunohistochemistry. Result: The identification of trophoblasts on each slide was defined according to positive staining and histologically chorionic villous similarity under microscopic examination, using the following five categories: none (1), less than five single positive-stained cells per-section (2), more than five single positive-stained cells per-section (3), clumps of positive-stained cells (4), and histological-like intact or fragmented chorionic villi (5). From amongst 71 samples that qualified for analysis, individual slides were evaluated and categorized into three groups, with the following results: 32 (45.1%) fell into group 1 (category 1) denoting a negative result, 10 (14.1%) fell into group 2 (category 2) indicating a possible positive result and 29 (40.8%) fell into group 3 (any combination of categories 3-5) representing a positive result. Conclusions: Fetal cells, identified by CK-7, can be found in more than 59.2% of the transcervical mucus in early pregnancy by use of a minimally invasive sampling method. Prenatal diagnosis of single-gene or chromosome disorders may be possible in the pregnant transcervical mucus by use of modern molecular methods and they deserve further study.