Chapman, D. A., Scott, K. G., & Mason, C. A. (2002).  Early risk factors for mental retardation: The role of maternal age and maternal education, American Journal on Mental Retardation, 107, 46-59.

The predictive value of maternal age and education in relation to rates of administratively defined mental retardation in a 3-year birth cohort (N=267,277) was studied.  Low maternal education placed individuals at increased risk for both educable mentally handicapped (EMH) and trainable mentally handicapped (TMH) placements.  Older maternal age was associated with increased risk of mental retardation, but for individuals with EMH, this age effect was only seen in the lowest education group.  In terms of population-level risk, it was younger mothers with 12 years of education or less whose births were associated with the greatest proportion of mental retardation.  From a public policy viewpoint, children born to mothers with low levels of education are an important group to target for prevention/early intervention efforts.