Risk of obstetric and perinatal complications in women presenting with breast cancer during pregnancy and the first year postpartum in Sweden 1973-2017: A population-based matched study.

INTRODUCTION: For women presenting with breast cancer during pregnancy, treatment guidelines were historically restricted to only surgical treatment. Over the past decades, chemotherapy administered during pregnancy has been gradually introduced. Although breast cancer treatments during ongoing pregnancy have been deemed safe, detailed information on potential obstetric risks is lacking. We aimed to assess the risk of adverse obstetric and perinatal outcomes of breast cancer in pregnancy and within 1 year postpartum and in relation to trimester at breast cancer diagnosis, tumor stage, and cancer treatment during pregnancy. MATERIAL AND METHODS: Population-based matched study. Women diagnosed with breast cancer during pregnancy in 1973-2017 were identified in the Swedish Cancer Register and the Medical Birth Register, with additional information from the National Quality Register for Breast Cancer. Each birth with maternal breast cancer (n = 208 pregnant, n = 672 postpartum) was matched by age, calendar year, and birth order to 10 unexposed births from cancer-free women in the population (n = 2080 and n = 6720). Adjusted conditional logistic and multinomial regression models were used to estimate odds ratios and relative risk ratios, commonly denoted relative risks (RR) with 95% confidence intervals (CI), of adverse obstetric and perinatal outcomes. RESULTS: Breast cancer during pregnancy was associated with higher risks of preterm birth, both planned (RR 67.1, 95% CI 33.2-135.6) and spontaneous preterm birth (RR 3.8, 95% CI 2.0-7.5), and low birthweight (<2500 g: RR 7.5, 95% CI 4.9-11.3). The associated risks were higher if the breast cancer was diagnosed in the second trimester, and of similar magnitude irrespective of stage and treatment groups. There was a higher risk of low birthweight for gestational age (<25th centile) if breast cancer was diagnosed in the first trimester (RR 2.8, 95% CI 1.1-7.3). Risks of other pregnancy complications were similar to those of unexposed women, as were risks of neonatal mortality and malformations. Postpartum breast cancer was only associated with bleeding during pregnancy (RR 1.6, 95% CI 1.0-2.8). CONCLUSIONS: Preterm birth and related adverse outcomes were more common in women diagnosed with breast cancer during pregnancy. Reassuringly, breast cancer was not associated with other maternal pregnancy complications or adverse outcomes in children.

Obstetric and perinatal outcomes in women with previous breast cancer: a nationwide study of singleton births 1973-2017.

STUDY QUESTION: What are the obstetric and perinatal outcomes in births to breast cancer survivors compared to women without previous breast cancer? SUMMARY ANSWER: Women who conceived during the first 2 years following a breast cancer diagnosis had a higher risk for preterm birth, induced delivery, and cesarean section, while no increased risks were observed in births conceived later than 2 years after a breast cancer diagnosis. WHAT IS KNOWN ALREADY: A recent meta-analysis found higher risks of cesarean section, preterm birth, low birthweight, and small for gestational age in pregnancies among breast cancer survivors. Less is known about rarer outcomes such as pre-eclampsia or congenital malformations. STUDY DESIGN SIZE DURATION: We conducted a population-based matched cohort study including all breast cancer survivors who gave birth to singletons 1973-2017 in Sweden, identified through linkage between the Swedish Cancer Register, the Medical Birth Register, and the National Quality Register for Breast Cancer. PARTICIPANTS/MATERIALS SETTINGS METHODS: Each birth following breast cancer (n = 926) was matched by maternal age at delivery, parity, and calendar year at delivery to 100 births in a comparator cohort of women (n = 92 490). Conditional logistic and multinomial regression models estimated relative risks (RR) with 95% CI. Subgroup analyses by time since diagnosis and type of treatment were performed. MAIN RESULTS AND THE ROLE OF CHANCE: Previous breast cancer was associated with higher risks of induced delivery (RR; 1.3, 1.0-1.6), very preterm birth (RR; 1.8, 1.1-3.0), and planned preterm birth (RR; 1.6, 1.0-2.4). Women who conceived within 1 year after breast cancer diagnosis had higher risks of cesarean section (RR; 1.7, 1.0-2.7), very preterm birth (RR; 5.3, 1.9-14.8), and low birthweight (RR; 2.7, 1.4-5.2), while the risks of induced delivery (RR; 1.8, 1.1-2.9), moderately preterm birth (RR; 2.1, 1.2-3.7), and planned preterm birth (RR; 2.5, 1.1-5.7) were higher in women who conceived during the second year after diagnosis. Women who conceived later than 2 years after breast cancer diagnosis had similar obstetric risks to their comparators. LIMITATIONS REASONS FOR CAUTION: As information on the end date of treatment was unavailable, the time between the date of diagnosis and conception was used as a proxy, which does not fully capture the effect of time since end of treatment. In addition, treatments and clinical recommendations have changed over the long study period, which may impact childbearing patterns in breast cancer survivors. WIDER IMPLICATIONS OF THE FINDINGS: Risks of adverse obstetric outcomes in breast cancer survivors were confined to births conceived within 2 years of diagnosis. As family building holds significance for numerous young breast cancer patients, these findings are particularly important to inform both breast cancer survivors and clinicians about future reproductive outcomes. STUDY FUNDING/COMPETING INTERESTS: This work was supported by the Swedish Cancer Society (grant number 22-2044 Pj A.L.V.J.), Karolinska Institutet Foundations (grant number: 2022-01696 F.E.L., 2022-01559 A.L.V.J.), and the Swedish Research Council (grant number: 2021-01657 A.L.V.J.). K.A.R.-W. is supported by grants from the Swedish Cancer Society (20 0170 F) and the Radiumhemmets Research Foundations for clinical researchers 2020-2026. The authors declare that they have no conflicts of interest. TRIAL REGISTRATION NUMBER: N/A.