Objective: Our aim was to determine the prevalence of maternal and neonatal vitamin B12 (vit-B12) and folate deficiencies, a new cutoff value of serum vit-B12 in newborns using vit-B12-related metabolites and also cutoff values of homocysteine (Hcy), propionyl (C3) carnitine, and methyl malonic acid (MMA) in newborns using a vit-B12 cutoff value of 200 pg/mL. Methods: Healthy pregnant women (without iron deficiency) and 98 healthy, term, singleton babies were included. Blood samples were obtained from women 0-8 h before birth and from cord blood during birth for hemogram and to measure serum vit-B12, folate, and Hcy levels. Maternal and cord blood serum vit-B12 levels were classified as low < 200 pg/mL, marginal 200-300 pg/mL, and normal >= 300 pg/mL. Neonatal urine MMA levels were analyzed in mothers with a vit-B12 concentration < 300 pg/mL. C3 carnitine levels of newborns were acquired from extended newborn screening. Receiver operating characteristics curve (ROC) analysis was used for serum vit-B12, urine MMA, C3 carnitine, and Hcy. Results: Of total, 98 pregnant women (28.6 +/- 5.5-year-old) and 98 newborn were included. Vit-B12 level was lower than 300 pg/mL in 93% of the pregnant women and 61% of cord blood samples. Folate deficiency was not found in either group. There was statistically significant negative correlation between baby C3 carnitine, cord blood folate (r = -0.265, p = .008) and cord blood vit-B12 (r = -0.220, p = .029). In backward stepwise linear regression analysis, maternal vit-B12 level exerted the most marked effect on cord blood vit-B12 level (adjusted R-2 = 0.457). In ROC analysis, the Hcy cutoff value was 4.77 mu mol/L (68.4% sensitivity, 58.3% specificity, p = .012) for the detection of vit-B12 deficiency. Conclusion: Vit-B12 deficiency remains an important health issue for pregnant women and newborns. Our study revealed a cutoff value for Hcy for the detection of nutritional vit-B12 deficiency that could be used in practice for newborns.