Adverse birth outcomes among offspring born to women diagnosed with cancer: a population-based cohort study.

[BACKGROUND] With increasing cancer incidence and survival rates, the prevalence of maternal cancer and its effect on adverse birth outcomes are important for prenatal care and oncology management. However, the effects of different types of cancer at different gestational stages have not been widely reported.

[OBJECTIVE] This study aimed to describe the epidemiologic characteristics of pregnancy-associated cancers (during and 1 year after pregnancy) and evaluate the association between adverse birth outcomes and maternal cancers.

[METHODS] Of 983,162 cases, a history of maternal cancer, including pregestational cancer, pregnancy-associated cancer, and subsequent cancer, was identified in 16,475 cases using a health information network. The incidence and 95% confidence interval of pregnancy-associated cancer were calculated with the Poisson distribution. The adjusted risk ratio with 95% confidence interval of the association between adverse birth outcomes and maternal cancer were estimated using the multilevel log-binomial model.

[RESULTS] A total of 38,295 offspring were born to mothers with a cancer history. Of these, 2583 (6.75%) were exposed to pregnancy-associated cancer, 30,706 (80.18%) had a subsequent cancer diagnosis, and 5006 (13.07%) were exposed to pregestational cancer. The incidence of pregnancy-associated cancer was 2.63 per 1000 pregnancies (95% confidence interval, 2.53‰-2.73‰), with cancer of the thyroid (1.15‰), breast (0.25‰), and female reproductive organs (0.23‰) being the most common cancer types. The increased risks of preterm birth and low birthweight were significantly associated with cancer diagnosed during the second and third trimester of pregnancy, whereas increased risks of birth defects (adjusted risk ratio, 1.48; 95% confidence interval, 1.08-2.04) were associated with cancer diagnosed in the first trimester. Increased risks of preterm birth (adjusted risk ratio, 1.16; 95% confidence interval, 1.02-1.32), low birthweight (adjusted risk ratio, 1.24; 95% confidence interval, 1.07-1.44), and birth defects (adjusted risk ratio, 1.22; 95% confidence interval, 1.10-1.35) were observed in thyroid cancer survivors.

[CONCLUSION] Careful monitoring of fetal growth should be implemented for women diagnosed with cancer in the second and third trimester to ensure timely delivery and balance the benefits of neonatal health and cancer treatment. The higher incidence of thyroid cancer and increased risk of adverse birth outcomes among thyroid cancer survivors suggested that the regular thyroid function monitoring and regulation of thyroid hormone levels are important in maintaining pregnancy and promoting fetal development among thyroid cancer survivors before and during pregnancy.