The Papanicolaou smear and the obstetric patient: a simple test with great benefits.

The Papanicolaou (Pap) smear is the most successful screening test for carcinoma in the history of medicine. Since its introduction in the early 1930s, the national death rate from cervical cancer has dropped 70%.1 The success of this test is mainly a result of its simplicity, low cost, and low false-negative rate. The Pap test’s main benefit is the early detection of preneoplastic lesions. The Pap test is also used to diagnose several infectious agents that manifest with specific cytologic features. Hormonal evaluation based on smears of the lateral vaginal wall is another important use of the Pap test. The obstetric patient should receive a Pap smear at her first prenatal visit as part of her initial evaluation. The cytologic findings of those smears in this particular group of women have been the subject of extensive research since the 1960s. This research has generally focused on the following areas: 1) the ability to accurately diagnose preneoplastic lesions during pregnancy in light of the numerous diagnostic pitfalls that result from the physiologic changes that occur during pregnancy;2,3 2) the use of hormonal evaluation and maturity index to predict fetal status, e.g., maturation, sex, placental activity, or an inevitable abortion;4–6 and 3) the detection and significance of inflammation and infectious agents.7–9 The incidence of squamous intraepithelial lesions (SIL) is increasing among sexually active females, especially those with sexually transmitted diseases (STD). In a study reviewing 98 pregnant and postpartum patients with abnormal Pap smears and directed biopsies, 67 were diagnosed with SIL. Of these 67, 18 had high-grade (HG) SIL and 49 had low-grade (LG) SIL.10 The most appropriate follow-up strategy for pregnant women with abnormal cervical cytology has also been the subject of extensive research. It is well-documented that cervical dysplasia diagnosed during pregnancy and followed by serial Pap smears until term may not necessarily progress and on occasions may even regress.11–13 Londo et al.14 found that postpartum Pap smears provide a higher yield of endocervical cells and better prediction of dysplasia than prepartum smears. Nonetheless, this does not lessen the importance of the initial smear, since a high number of these patients may be lost to follow-up through noncompliance.11,14 Interpretation of Pap smears obtained from pregnant patients can be difficult. Knowledge of the pitfalls unique to pregnancy can minimize diagnostic errors in most cases.10 The most common pitfall is misinterpreting decidua cells for SIL. Decidua cells may mimic LGSIL, HGSIL, and carcinoma. Decidua cells that slough off the free surface of the uterus may degenerate and acquire pyknotic nuclei and orangeophilic cytoplasm and be mistaken for squamous-cell carcinoma.15 During pregnancy, endocervical glands become hyperplastic and hypertrophied, and may undergo Aria-Stella-type changes. These changes are often overdiagnosed as atypical glandular cells of undetermined significance.10,16 Even years after pregnancy, involuted decidua and trophoblasts can mimic HGSIL and lead to inappropriate treatment.17 Based on specific cytologic criteria, the diagnoses of candida, trichomonas, herpes simplex virus, and human papilloma virus can be reliably rendered on Pap smears.18 Although Clamydia trachomatis and gonococcal species cannot be accurately diagnosed on Pap smears due to the lack of specific cytologic features, they are frequently associated with inflammatory exudate and reactive cellular changes.19 Inflammation by itself on Pap smears is not necessarily indicative of infection, and an inflammatory component is commonly seen on Pap smears from pregnant women.20,21 Unfortunately, the significance of a marked inflammatory exudate in the pregnant population has not been adequately evaluated. Since patients with sexually transmitted diseases (STD) have a higher risk of preterm delivery and fetal morbidity, it is important to evaluate whether inflammation and/or the reactive changes caused by Department of Pathology, University of Michigan, Ann Arbor, Michigan *Correspondence to: Claire W. Michael, M.D., Department of Pathology, University of Michigan, 1500 E. Medical Center Dr., Room 2G332/Box 0054, Ann Arbor, MI 48109. Received and accepted 16 March 1999