Background Low birth weight is a key underlying factor in neonatal mortality, which is the leading cause of death i n children under five years of age. The causes of IUGR can be maternal, placental, fetal, genetic cause or combination of these factors. Maternal causes include age, multiparty, nutritional deficiency, medical disorders, medications, substance abuse. According to some recent studies early detection of Maternal Vitamin B12 deficiency in pregnancy and appropriate interventions are likely to reduce incidence of IUGR. Therefore we conduct a prospective observational study in a cohort of pregnant women to investigate the maternal determinant of risk of IUGR and to analyze maternal Vitamin B 12 status and role of its deficiency towards the risk of IUGR. Methods Prospective cohort study. After obtaining ethical clearance study subjects counseled about the study and informed consent obtained. In our study we found low maternal vitamin B12 is directly associated with IUGR & Low birth weight. In our study low APGAR score babies & SNCU admission is significantly higher among mothers with low serum vitamin B12. This may be due to preterm birth& IUGR.