An aim of this study was to evaluate an effect of misinterpretation of pregnancy related cellular changes on the postpartum regression rate of abnormal cervical smears in pregnancy. A series of 265 cases with abnormal cervical smears in pregnancy were selected from a database of cervical smear results. The selected cases were classified as regression, persistence, and progression based on the results of postpartum cervical smears and histology. Of the selected cases, 162 cases were classified as regression and the postpartum regression rate was 61.1% (162/265). We reviewed abnormal cervical smears in pregnancy these cases. The primary cytologic diagnoses of these cases were ASCUS (118 cases), AGUS (2 cases), ASCUS/AGUS (1 case), LSIL (25 cases), LSIL R/O HSIL (2 cases), and HSIL (14 cases). With information of the pregnacy, we identified decidual cells in 24 cases, but cells identified by the Arias-Stella reaction and trophoblasts were not found. Sixteen cases out of 162 cases were reclassified as a pregnancy related change rather than an abnormal. Desidual cells were considered as ASCUS in 15 cases and as LSIL in one case. The revised postpartum regression rate was 55.5%(147/265) and was lower than the original. Consequently, misinterpretation of the pregnancy related cellular changes has an effect on a rise of the postpartum regression rate of the abnormal cervical smear in pregnancy. Pathologists may diagnose pregnancy related cellular changes as abnormal findings if they do not have information regarding the pregnancy. Therefore, clinical information of pregnancy and knowledge about the pregnancy related cellular changes are essential to prevent misinterpretation.