The mediating role of socioeconomic status on the relationship between pregnancy history and later-life cognition.

OBJECTIVE: The association of pregnancy with later-life cognition is not well understood. We examined whether full-term and incomplete pregnancies were associated with cognition in a sample of postmenopausal women, and whether socioeconomic status (SES) factors mediated these relationships.

METHODS: A total of 1016 cognitively normal women from the National Health and Nutrition Examination Survey (NHANES) were examined. Cognitive measures included the Digit Symbol Substitution Test (DSST), Animal Fluency (AF) and the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) Word Learning (CERAD-WL) and Delayed Recall (CERAD-DR) tasks. Analyses examined the relationship between the number of term and incomplete pregnancies with cognitive performance, as well as the mediating effects of education and the federal income-to-poverty ratio (PIR).

RESULTS: A greater number of term pregnancies was associated with worse performance on the DSST ( β  = -0.09, 95% confidence interval [CI]: -0.12, -0.06), AF ( β  = -0.03, 95% CI: -0.07, 0.00) and CERAD-DR ( β  = -0.04, 95% CI: -0.08, -0.01). More incomplete pregnancies were associated with better CERAD-DR performance ( β  = 0.07, 95% CI: 0.01, 0.13), and 28% (95% CI: 0.17, 0.42) of the association of term pregnancies with the DSST was mediated by the PIR.

CONCLUSIONS: A higher number of term pregnancies was associated with worse cognitive performance, whereas a higher number of incomplete pregnancies was associated with better cognitive performance. Results indicate the necessity to consider SES factors when studying the relationship between pregnancy and cognition.