Association between having a pregnancy complicated by vaginal bleeding and risk of cancer

ABSTRACT Background A full-term pregnancy is associated with a lower cancer risk. The risk of cancer in women with vaginal bleeding in pregnancy is unknown. Methods We conducted a registry-based cohort study (1995-2017) in Denmark. We included pregnancies (n=37 082) affected by vaginal bleeding (VB) within 20 gestational weeks among 35 514 women, VB-unaffected pregnancies (n=1 363 614) among 783 314 women, pregnancies ending in a termination (n=324 328) among 239 638 women or miscarriage (n=137 104) among 121 353 women. We computed absolute risk of cancer and hazard ratios (HR) with 95% confidence intervals (CI) adjusted for age, calendar year, morbidity, and socioeconomic factors using Cox proportional hazards regression. Results At the end of the 24-year follow-up, there were 1 320 events among VB-affected cohort, 40 420 events among VB-unaffected cohort, 10 300 events among termination cohort, and 4 790 events among miscarriage cohort. The HR for any cancer was 1.03 (95% CI: 0.97-1.08) when comparing VB-affected vs VB-unaffected pregnancies, 1.03 (95% CI: 0.97-1.09) vs terminations, and 0.90 (95% CI: 0.84-0.95) vs miscarriages. Similar results were obtained for site-specific cancers. Conclusions We found no strong evidence for an association between vaginal bleeding in pregnancy and an increased risk of cancer.