Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Maternal vitamin B12 deficiency has been associated with disturbed cognitive functioning in offspring at different ages during childhood. However, this association has not been explored in pre‐school‐age children. The objective of this study was to examine the association between maternal vitamin B12 levels at the beginning and end of pregnancy and cognitive functioning in their children at 4 years of age. This longitudinal prospective study included a subsample of pregnant women and their children aged 4 years (<jats:italic>n</jats:italic> = 249) who participated in the ECLIPSES Study conducted in the province of Tarragona, Spain, from 2013 to 2017. Maternal vitamin B12 concentrations were determined in the first and third trimesters, and sociodemographic, nutritional and psychological data were collected. The children's cognitive functioning was assessed using the Wechsler Preschool and Primary Scale of Intelligence (WPPSI‐IV) and subtests of the Neuropsychological Assessment of Development (NEPSY‐II). The multivariable models showed a significant relationship between vitamin B12 and the working memory index in the first trimester of the pregnancy but not in the third trimester. Children of mothers in the second vitamin B12 level tertile (314–413 pg/mL) (<jats:italic>β</jats:italic> = 6.468, 95% confidence interval [CI]: = 2.054, 10.882, <jats:italic>p</jats:italic> = 0.004) and third vitamin B12 level tertile (≥414 pg/mL) (<jats:italic>β</jats:italic> = 4.703, 95% CI: = 0.292, 9.114, <jats:italic>p</jats:italic> = 0.037) scored higher in the working memory index of the WPPSI‐IV than the children of mothers with vitamin B12 levels in the first tertile (<314 pg/mL). Maintaining an adequate level of maternal vitamin B12 during early pregnancy contributes to improved performance in childhood working memory at 4 years of age.</jats:p>