Objective: To estimate the incidence of pregnancy-associated cancer during a 30-year period in Denmark on the basis of both births and abortions with and without age adjustment and age standardization.
Methods: Using data from the nationwide Danish registries, we investigated the occurrence of pregnancy-associated cancer (defined as cancer diagnosed during pregnancy and up to 1 year after pregnancy has ended) in pregnancies resulting in a birth (live birth or stillbirth) or an abortion. We included patients with primary cancer diagnosed at ages 15-44 years during 1977-2006 according to the Danish Cancer Registry. The patients were linked to the Medical Birth Registry, the Registry for Induced Abortions, and the National Patient Registry to obtain information on pregnancies.
Results: We identified 2,426 patients with pregnancy-associated cancer. The three most frequent types were melanoma, cervical cancer, and breast cancer. We found an increase in the total numbers of all pregnancy-associated cancers from 572 cases during 1977-1986 to 1,052 cases during 1997-2006. The proportions of all pregnancy-associated cancers among all cancers increased from 5.4% to 8.3% during the same periods. The overall crude incidence rate of all pregnancy-associated cancer was 89.6 out of 100,000 pregnancies. The crude incidence increased over time, with an average annual percentage change of 2.9% (95% confidence interval [CI] 2.4-3.3). After age adjustment, the increase was still statistically significant (1.6%, 95% CI 1.1-2.1).
Conclusion: We found a statistically significant increase in pregnancy-associated cancer during the 30-year study period. The tendency to postpone childbirth only partly explains the increase in incidence rates.
Level of evidence: III.