Effect of an antepartum Pap smear on the coverage of a cervical cancer screening programme:: a population-based prospective study

Background: Almost one-third of Norwegian women aged 25 - 69 years invited to have a Pap smear do not attend during the recommended period, and thus constitute a population with high-risk of cervical cancer ( CC). Since the incidence of precancerous lesions of the cervix peak with occurrence of pregnancies within the same decade in women aged 25 to 35 years of age, antepartum care presents an opportunity to offer a Pap smear thereby increasing the coverage of the programme. The study objective was to describe the effect of the antepartum Pap smear on the coverage of a cytological CC screening programme. Methods: Among 2 175 762 women resident in Norway in 31.12.1996, all women who gave birth in 1996 - 7 were identified from the Medical Birth Registry of Norway. Attendance to the cervical cancer screening was assessed by linkage to the Cytology Registry separately for the pregnant and non-pregnant women cohorts. The results were stratified by age, history of previous Pap smear and history of invitation to the CC screening programme. Logistic regression was used to estimate the relative probabilities of having a Pap smear adjusted for age, screening history, and time since invitation, for pregnant and non-pregnant women, respectively. Results: 69% of the pregnant women had a Pap smear during one year of follow-up since beginning of the pregnancy with the majority taken during the antepartum period. Irrespectively of age or history of having a Pap smear, pregnant women were 4.3 times more likely to have a Pap smear during follow-up compared to non-pregnant women. 63.2% of the pregnant women had a smear as response to the invitation letter compared to 28.7% of the non-pregnant women, OR = 2.1 (95% CI 1.9 to 2.4). As an indication of over-screening, 5397 pregnant women (57.8%) with a smear shortly before the start of follow-up also had a new Papsmear, compared to 83 023 (32.3%) in nonpregnant. Conclusion: Pap smear screening during pregnancy increases the coverage of the CC screening programme. The contribution of the antepartum Pap smear to over-screening exists but its effect is modest in countries where women on average become pregnant after the start of recommended age of screening.