Pregnancy itself is not a contraindication to performing a Pap smear. It is recommended that Pap smears be offered to women where appropriate i) until at least 28 weeks of pregnancy, and ii) in special cases, during the third trimester (particularly, if she is likely to have difficulty in participating in screening after delivery). The belief that Pap smears are associated with increased rates of miscarriage or pre-term labour is a misconception that can contribute to unwillingness of women to have Pap smear taken in pregnancy. In such cases, a Pap smear can be postponed until the pregnancy is safely established. Similarly, every woman with unexplained bleeding in early pregnancy should have her cervix visualised via a speculum to ensure that unexpected malignancy is not the cause and should have her Pap smear repeated. It is important to recognize the pitfals in cytology during pregnancy, decribed here.
Reports of absent endocervical component are more common in pregnancy. The use of a nylon or plastic brush and spatula in pregnant women has been shown e.g. in a Cochrane review to provide the highest rate of adequate smears. The plastic Cervex brush used under direct vision is another appropriate tool, whereas the use of Cytobrush is not recommended after 10 weeks of pregnancy. LBC is indicated if the smear is contaminated with mucus, which is often the case during pregnancy.
In pregnancy, the cervix undergoes both glandular and stromal changes, similar to those occurring in the endometrium. The endocervical glands become hyperplastic and result in a polypoid protrusion and increase in the tunnel clusters, and/or microglandular hyperplasia. These hypersecretory cells contribute to the thick mucous plug, sealing off the endometrial cavity from the vagina, with a substantial amount of immature squamous metaplasia as the result. The stroma can also undergo focal or massive decidualization, which could be the cause of vaginal spotting in pregnancy. Occasionally the glandular cells exhibit nuclear clearing and can also undergo Arias-Stella reaction. Perinuclear halos induced by glycogen as well as squamous-like syncytiotrophoblasts could mimic HPV. Endocervical cells with multi-nucleation or nuclear clearing could mimic herpes HSV infection. Cytotrophoblasts or degenerated decidual cells could mimic HGSIL. Despite the caution required in this population, dysplastic changes should not be underestimated.
For cytologists, it is essential to be familiar with the pregnancy-related changes to avoid misinterpretations. If, however, a high grade abnormality is confirmed, the management during pregnancy should follow the same guidelines as for the non-pregnant woman.