BRIDGING CLINICAL, METABOLIC, AND NUTRITIONAL FINDINGS IN MOTHER¿INFANT DYADS WITH MATERNAL VITAMIN B12 DEFICIENCY IDENTIFIED THROUGH NEWBORN SCREENING

Vitamin B12 is an essential micronutrient for foetal and postnatal neurological development. Its deficiency during pregnancy directly affects the newborn and can be detected through Expanded Newborn Screening (ENS), which enables the identification of maternal deficiency by detecting elevated biomarkers of B12 metabolism. In this thesis, a prospective observational study was conducted at the Vittore Buzzi Children’s Hospital in Milan (November 2021–August 2025), including 127 cases of maternal vitamin B12 deficiency identified among 249,715 newborns screened by ENS. Newborns underwent nutritional and metabolic blood tests, as well as stool collection for microbiota analysis; follow-up visits included clinical and neurodevelopmental reassessments. Mothers were evaluated through clinical and dietary history, with analysis of dietary patterns and supplementation during pregnancy. At the first admission, before hydroxycobalamin intramuscular administration, newborns showed mean values of vitamin B12 178.78 pg/ml (SD ± 82.44), homocysteine 18.01 μmol/L (SD ± 7.48; n.v. <10), plasma methylmalonic acid 3.89 μmol/L (SD ± 3.26; n.v. 0–4), and urinary methylmalonic acid 63.46 μmol/L (SD ± 65.42; n.v. 0–2). After the first intramuscular injection, mean values normalised rapidly (vitamin B12 1163 pg/ml; homocysteine 4.32 μmol/L; plasma methylmalonic acid 0.43 μmol/L; urinary methylmalonic acid 4.5 μmol/L). Only 7% showed mild initial signs of neurological immaturity, which fully resolved within 6 months of life. In the maternal group, mean vitamin B12 intake during pregnancy was 2.72 µg/day (range 0.01–7.03); only 11.8% met the EFSA Adequate Intake for vitamin B12. The majority reported an omnivorous diet (72.5%, n=92), while 17.3% (n=22) were lacto-vegetarian, 9.4% (n=12) lacto-ovo-vegetarian, and 0.8% (n=1) vegan. B12 intake decreased progressively from 2.9 µg/day in omnivores to 0.3 µg/day in vegans. Most B12 deficiencies (88.2%) were attributable to isolated low dietary intake, while 12.5% of women reported no supplementation during pregnancy. Microbiota analysis was conducted on 17 newborns at T0 (pre-supplementation) compared with age-matched healthy controls and it revealed a significant reduction in Proteobacteria (p = 0.035), Enterobacteriaceae (p = 0.036), and Akkermansiaceae (p = 0.027), with confirmation at the genus level for Akkermansia (p = 0.027). Moreover, laboratory studies on methods for total vitamin B12 measurement showed substantial variability among the main methods, leading to poor applicability of NICE recommended thresholds to detect B12 deficiency. In summary, ENS proved to be an effective tool for the early identification of subclinical vitamin B12 deficiencies of maternal origin. The findings emphasize the need for preconception preventive strategies, multidisciplinary management models, and improved diagnostic laboratory methods.