Pregnancy outcomes in survivors of adolescent and young adult breast cancer: a population-based cohort study

Abstract

Purpose: This study aimed to describe differences between adolescent and young adult (AYA) breast cancer (BC) survivors and women with no cancer history (unexposed); estimate the risk ratios of preterm birth, small for gestational age, Caesarean section (CS), preeclampsia, and/or severe maternal morbidity among AYA BC survivors compared to unexposed individuals; and investigate the effect of mode of conception on observed associations. Methods: A retrospective cohort was created using administrative health data. All live singleton and multiple hospital births >22 weeks’ gestation to women in Ontario aged 15-50 between April 2006 to March 2018 were included. Exposed were AYA BC survivors and their infants (N=474 pairs) and unexposed included women with no cancer history and their infants (N=1,189,506 pairs). Standardized differences were used to assess demographic differences by exposure status. Modified Poisson regression was used to estimate risk ratios for adverse pregnancy outcomes among AYA BC survivors compared to unexposed individuals, adjusting for potential confounders. Stratified analysis by mode of conception was performed to investigate effect modification. Results: Mean time from BC diagnosis to index pregnancy was 4.9 (SD 3.2) years. AYA BC survivors were older at delivery, more likely to have a higher income quintile, live in urban areas, have chronic hypertension, and have alcohol exposure during pregnancy, but were less likely to smoke during pregnancy than unexposed women. In adjusted models, AYA BC was associated with CS (RR 1.26, 95% CI 1.14-1.39); the other outcome models did not yield clinically important findings. Time between BC diagnosis and pregnancy and exposure to chemotherapy did not affect risk of adverse pregnancy outcomes. When investigating CS subtypes, AYA BC exposure was associated with increased risk of both planned (RR 1.27, 1.08-1.49) and unplanned CS (RR 1.41, 1.20-1.66). The relationship observed between AYA BC and CS persisted among singleton pregnancies, and did not differ significantly by mode of conception. Conclusions: AYA BC diagnosis was only associated with increased risk of CS. This increased CS risk is not explained by mode of conception. Risk of adverse pregnancy outcomes does not appear to be a reason to delay pregnancy among AYA BC survivors.