Introduction: Cancer during pregnancy is rare, but there is concern that the rate will increase as maternal age increases.
Objectives: This study aimed to determine trends in pregnancy-associated cancers between 1994 and 2007, and the associations between maternal cancer and pregnancy outcomes.
Methods: The study population comprised 781,907 women giving birth in NSW between 1994 and 2008. Cancer and maternal information were obtained from linked records of NSW Central Cancer Registry, NSW Perinatal Data Collection, and NSW Admitted Patient Data Collection. The Cochran-Armitage test was used to analyse trends, and the generalised estimating equations with a logit link were used to examine associations. Adjusted odds ratios (aOR) with 95% confidence interval (CI) were calculated.
Results: A total of 1,798 new cancer diagnoses were identified, including 499 during pregnancy and 1,299 postpartum. From 1994 to 2007, the crude incidence rate of pregnancy-associated cancer increased from 112.3 to 191.5 per 100,000 maternities (P < 0.001) and only 14% of the increase was explained by increasing maternal age. Cancer diagnosis was more common than expected in women aged 15–44 years (observed-to-expected ratio 1.49, 95% CI 1.42–1.56). Cancers were predominantly melanoma (33.3%) and breast cancer (21.0%). Women with cancer diagnosed during pregnancy had high rates of labour induction (28.5%), caesarean section (40.0%) and planned preterm birth (19.7%). Novel findings included a cancer association with multiple pregnancies (aOR 1.52, 95% CI 1.13–2.05) and LGA (aOR 1.47, 95% CI 1.14–1.89).
Conclusions: Pregnancy-associated cancers have increased, and this increase is only partially explained by increasing maternal age. Pregnancy increases women’s interaction with health services and the possibility for diagnosis, but may also influence tumour growth.