Residual trophoblastic tissue as a source of highly atypical cells in the postpartum cervicovaginal smear

A cervicovaginal smear containing atypical cells, which were interpreted as dysplastic cells, was obtained from a women one-year postpartum. These cells were seen singly, in small groups and in clusters embedded in an amorphous pink matrix. They had amphophilic cytoplasm and increased nuclear/cytoplasmic ratios, as well as hyperchromatic nuclei with variably prominent nucleoli, features that are characteristic of trophoblastic cells. No evidence of dysplasia was seen on subsequent colposcopic examination or cervical biopsy. Endocervical curettage yielded fragments of exfoliated endometrium and residual trophoblastic tissue associated with a placental implantation site. Although involution of the placental site is generally complete by six to seven weeks postpartum, maternal-fetal tissue may in fact continue to be exfoliated for several months or longer after delivery. If seen on a cervicovaginal smear, these cells can be highly atypical and may be mistaken as dysplastic or malignant. The cytologic features that characterize trophoblasts and their persistence in postpartum cervicovaginal smears are discussed.