Does prenatal maternal stress impair cognitive development and alter temperament characteristics in toddlers with healthy birth outcomes?

AIM: The aim of this study was to assess the cognitive and behavioural development of children with healthy birth outcomes whose mothers were exposed to prenatal stress but did not experience pregnancy complications. METHOD: In this prospective study, self-reported data, including the Prenatal Life Events Checklist about stressful life events (SLEs) during different stages of pregnancy, were collected at 32 to 34 weeks' gestation. Thirty-eight healthy females (mean age 27 y 8 mo, SD 2 y 4 mo) who were exposed to severe SLEs in the first trimester were defined as the exposed infant group, and 114 matched comparison participants were defined as the unexposed infant group (1:3). Maternal postnatal depressive symptoms were assessed with the Edinburgh Postnatal Depression Scale. The Bayley Scales of Infant Development and the Toddler Temperament Scale were used to evaluate the cognitive development and temperament characteristics of the infants with healthy birth outcomes when they were 16 to 18 months old. RESULTS: A randomized block multivariate analysis of covariance showed that the mental development index scores of the infants of mothers with prenatal exposure to SLEs in the first trimester averaged seven points (95% confidence interval 3.23-10.73 points) lower than those of the unexposed infants. Moreover, the infants in the exposed group achieved higher scores for regularity (adjusted mean SD 2.77 0.65 vs. 2.52 0.78, F(5,146) =5.27, p=0.023) and for persistence and attention span (adjusted mean 3.61 0.72 vs. 3.35 0.52, F(5,146) =5.51, p=0.020). INTERPRETATION: This study provides evidence that lower cognitive ability and less optimal worse behavioural response in infants might independently result from prenatal maternal stress.