ObjectiveTo investigate the effects of completed pregnancy with childbirth and incomplete pregnancy without childbirth on the late-life cognition and the risk of Alzheimer disease (AD) in women.MethodsUsing the pooled data of 3,549 women provided by 2 population-based cohort studies, we conducted logistic regression analyses to examine retrospectively the associations of completed and incomplete pregnancy with the risks of mild cognitive impairment and AD. For women without dementia, we also conducted analyses of covariance to examine the associations of completed and incomplete pregnancy with Mini-Mental State Examination (MMSE) score.ResultsGrand multiparous women who experienced ≥5 completed pregnancies showed an ≈1.7-fold higher risk of AD than those who experienced 1 to 4 completed pregnancies (odds ratio [OR] 1.68, 95% confidence interval [CI] 1.04–2.72), while those who had incomplete pregnancies showed half the level of AD risk compared with those who never experienced an incomplete pregnancy (OR 0.43, 95% CI 0.24–0.76 for 1 incomplete pregnancy; OR 0.56, 95% CI 0.34–0.92 for ≥2 incomplete pregnancies). In women without dementia, the grand multiparous had worse MMSE scores than those with 1 to 4 completed pregnancies (p < 0.001), while those who experienced ≥1 incomplete pregnancies had better MMSE scores than those who never experienced an incomplete pregnancy (p = 0.008).ConclusionsGrand multiparity was associated with high risk of AD, while incomplete pregnancy was associated with low risk of AD in late life.