Sourander A, Upadhyaya S, Surcel HM, et al. - In view of inconsistent findings from prior studies on maternal 25(OH)D levels during pregnancy and offspring autism spectrum disorder (ASD) are inconsistent, researchers herein sought to examine the correlation between maternal 25(OH)D levels during pregnancy and offspring ASD by using a nationwide population-based register data with a nested case-control study design. Cases were ASD patients (n = 1,558) born from 1987 to 2004 and received a diagnosis of ASD by 2015; these were matched with an equal number of controls. Per analyses, the risk of ASD was higher in correlation with deficient (< 30 nmol/L) and insufficient maternal 25(OH)D levels (30 - < 50 nmol/L) compared with sufficient maternal 25(OH)D levels. This finding may aid in understanding the role of maternal vitamin D during fetal brain development and increased risk of ASD.