Abstract
Background. High maternal age is a well-recognized risk factor for Down's syndrome. There are also several studies of a possible effect of paternal age, but no consistent evidence of an association is found. Less is known about any effects of the age of grandparents. Objective. To assess whether maternal or paternal grandparents’ age is associated with the risk of Down's syndrome. Methods. We used logistic regression analyses with data from the Medical Birth Registry of Norway, adjusting for possible confounding factors. Results. We found no evidence of an association with the risk of Down's syndrome either for a maternal grandmother's age (odds ratio 0.9, 95% confidence interval 0.6–1.5 per 10-year increase in grandmother's age) or for any of the other grandparents’ age. Conclusions. High maternal age remains the only well-established age-related risk factor for Down's syndrome. There is little evidence that the increased risk represented by older mothers is passed on to offspring of her non-affected daughters.