Abstract
Background Uncontrolled studies have reported associations between later Parkinson's disease onset in women and a history of giving birth, with age at onset delayed by nearly 3 years per child. We tested this association in two independent data sets, but, as a control to test for nonbiological explanations, also included men with PD. Methods We analyzed valid cases from the Parkinson's Progressive Markers Initiative incident sample (145 women, 276 men) and a prevalent sample surveyed by the New Zealand Brain Research Institute (210 women, 394 men). Results The association was present in both women and men in the Parkinson's Progressive Markers Initiative study, and absent in both in the New Zealand Brain Research Institute study. This is consistent with generational differences common to men and women, which confound with age at onset in incident-dominant samples. Conclusions Despite being replicable in certain circumstances, associations between childbirth and later PD onset are an artifact of generational cohort differences. (c) 2020 International Parkinson and Movement Disorder Society