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Objectives Besides the inherited form, vitamin B 12 deficiency may be due to diet restrictions or abnormal absorption. The spread of newborn screening programs worldwide has pointed out that non-inherited conditions are mainly secondary to a maternal deficiency. The aim of our work was to study seven cases of acquired vitamin B 12 deficiency detected during our newborn screening project. Moreover, we aimed to evaluate vitamin B 12 and related biochemical parameters status on delivering female to verify the consequences on newborns of eventually altered parameters. Design and methods 35,000 newborns were screened; those showing altered propionyl carnitine (C3) underwent second-tier test for methylmalonic acid (MMA) on dried blood spot (DBS). Subsequently, newborns positive to the presence of MMA on DBS and their respective mothers underwent further tests: serum vitamin B 12 , holo-transcobalamin (Holo-TC), folate and homocysteine; newborns were also tested for urinary MMA content. A control study was conducted on 203 females that were tested for the same parameters when admitted to hospital for delivery. Results Approximately 10% of the examined newborns showed altered C3. Among these, seven cases of acquired vitamin B 12 deficiency were identified (70% of the MMA-positive cases). Moreover, our data show a high frequency of vitamin B 12 deficiency in delivering female (approximately 48% of examined pregnants). Conclusions We suggest to monitor vitamin B 12 and Holo-TC until delivery and to reconsider the reference interval of vitamin B 12 for a better identification of cases at risk. Finally, newborns from mothers with low or borderline levels of vitamin B 12 should undergo second-tier test for MMA; in the presence of MMA they should be supplemented with vitamin B 12 to prevent adverse effects related to vitamin B 12 deficiency. [ABSTRACT FROM AUTHOR]