Maternal use of hormonal contraception and rare cancer types in children: A nationwide PECH cohort study

Abstract Background Maternal hormonal contraception use has been associated with an increased risk of leukaemia and central nervous system (CNS) tumours in children. However, little is known about the association with other, less common childhood cancer types. We assessed associations between maternal hormonal contraceptive use and all main types of childhood cancer, excluding leukaemia and CNS tumours. Methods In this nationwide PECH cohort study, we followed all Danish children liveborn in 1996–2014 ( n = 1 185 063) from birth until 2018. Registry information was extracted on maternal filled prescriptions of hormonal contraception and childhood cancer diagnoses (age at diagnosis <20 years). The exposure of interest was maternal ‘recent use’ of hormonal contraception (use ≤3 months before or during pregnancy, except for injections, implants and intrauterine devices with a different timeframe), compared to no use. Cox proportional hazard models were used to estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for childhood cancer according to any use, regiment (combined/progestin‐only) and administration route (oral/non‐oral). Results During 15 335 990 person‐years of follow‐up, 1384 children were diagnosed with a rare cancer type. Compared to children of mothers with no use of hormonal contraception, maternal recent use of hormonal contraception was not statistically significantly associated with any of the childhood cancers assessed. Except for maternal recent use of non‐oral hormonal contraception, where a hazard ratio (HR) of 6.90 (95% CI: 1.31, 36.47) for hepatic tumours was found. However, this finding was based on a small number of children and if causal, this would result in one additional case per about 99 500 person‐years of follow‐up. Conclusions Maternal use of hormonal contraception up to or during pregnancy was not associated with nearly every rare childhood cancer type assessed, compared to no use.