BACKGROUND: The relationship between the prenatal environment, maternal-fetal interaction, and allergic disease in the offspring remains understudied. OBJECTIVE: We sought to determine whether gestational diabetes (GDM) modifies the risk of early childhood atopic manifestations, including atopic dermatitis and allergen sensitization. METHODS: This study includes 680 children from the Boston Birth Cohort. Mother-child dyads were recruited at birth and followed prospectively to a mean age of 3.2 +/- 2.3 years, with study visits aligned with the pediatric primary care schedule. The primary outcomes were physician-diagnosed atopic dermatitis on standardized medical record abstraction and allergen sensitization based on ImmunoCAP to 7 common foods and 5 common aeroallergens (specific IgE, >or=0.10 kUA/L; Phadia, Uppsala, Sweden). GDM was determined by means of standardized medical record review. Logistic regression analysis, stratified by term/preterm status, evaluated the association of GDM with atopic dermatitis and allergen sensitization, respectively, controlling for maternal prepregnancy body mass index, fetal growth, and pertinent covariates. RESULTS: Of the 680 children, 488 were term, and 192 were preterm (<37 weeks' gestation). Overall, 4.9% of the mothers had GDM. Among the 680 children, 34.4% had atopic dermatitis, and 51% had allergen sensitization. In term births GDM was significantly associated with atopic dermatitis (odds ratio [OR], 7.2; 95% CI, 1.5-34.5) and allergen sensitization (OR, 5.7; 95% CI, 1.2-28.0). Adjusting for fetal growth had little effect. The association with sensitization was driven primarily by food sensitization (OR, 8.3; 95% CI, 1.6-43.3). The above associations were not observed in preterm births. CONCLUSIONS: In term births GDM increased the risk of atopic dermatitis and early childhood allergen sensitization independently of maternal prepregnancy body mass index and fetal growth.