Stress during pregnancy affects general intellectual and language functioning in human toddlers

Prenatal maternal stress has been shown to impair functioning in nonhuman primate offspring. Little is known about the effects of prenatal stress on intellectual and language development in humans because it is difficult to identify sufficiently large samples of pregnant women who have been exposed to an independent stressor. We took advantage of a natural disaster (January 1998 ice storm in Québec, Canada) to determine the effect of the objective severity of pregnant women's stress exposure on general intellectual and language development of their children. Bayley Mental Development Index (MDI) scores and parent-reported language abilities of 58 toddlers of mothers who were exposed to varying levels of prenatal stress were obtained at 2 y of age. The hierarchical multiple regression analyses indicated that the toddlers' birth weight and age at testing accounted for 12.0% and 14.8% of the variance in the Bayley MDI scores and in productive language abilities, respectively. More importantly, the level of prenatal stress exposure accounted for an additional 11.4% and 12.1% of the variance in the toddlers' Bayley MDI and productive language abilities and uniquely accounted for 17.3% of the variance of their receptive language abilities. The more severe the level of prenatal stress exposure, the poorer the toddlers' abilities. The level of prenatal stress exposure accounted for a significant proportion of the variance in the three dependent variables above and beyond that already accounted for by non-ice storm-related factors. We suspect that high levels of prenatal stress exposure, particularly early in the pregnancy, may negatively affect the brain development of the fetus, reflected in the lower general intellectual and language abilities in the toddlers.