The clinical implications of abnormal cervical cytology during pregnancy are unclear. Therefore, we performed the present study to determine the role of cervical cytologic screening during pregnancy in association with placental abnormalities and preterm birth. A review of 2,480 cases during 11 years revealed significant correlation of reactive, infectious, atypical, and dysplastic cytologic changes during pregnancy with abnormal placental findings. Also, all but dysplastic cytologic changes were significantly associated with preterm birth. Furthermore, we observed significant association of the presence of high-risk human papillomavirus (HPV) DNA with preterm birth and placental abnormalities. These findings indicate that cervical infection of HPV is a risk factor for preterm birth and that cervical cytology is an effective tool for screening women for infection and inflammation during pregnancy and predicting pregnancy outcome.