Objective:To study the incidences of vitamin K 1 and K 2 deficiency (VKD) in umbilical cord blood (UBC) of neonates and the dynamic changes and influencing factors of serum vitamin K 1 levels after preventive vitamin K 1 supplementation. Methods:From January 2021 to June 2022, neonates born in the Obstetrics Department of our hospital were prospectively enrolled and the levels of vitamin K 1 and K 2 in UBC and serum vitamin K 1 levels at 14 d and 28 d after vitamin K 1 supplementation were measured. The neonates were assigned into hospitalization group and healthy group and further assigned into early-preterm, late-preterm and full-term groups based on gestational age (GA). The incidences of VKD of different GA were studied. Dynamic changes of vitamin K 1 levels were calculated. Multivariate logistic regression was used to analyze the influencing factors of vitamin K 1 levels in hospitalization group at 28 d. Results:A total of 100 neonates were included. 80 neonates were hospitalized, including 25 early-preterm, 25 late-preterm and 30 full-term. 20 were healthy full-term neonates. No significant differences existed in the incidences of VKD of different GA ( P>0.05), however, the overall incidences were high (82.0% and 84.0%, respectively). After preventive vitamin K 1 supplementation, the levels of vitamin K 1 in full-term and preterm groups at 14 d were higher than at birth and 28 d. The levels of vitamin K 1 in hospitalized full-term neonates at 14 d and 28 d were higher than hospitalized preterm neonates. The levels of vitamin K 1 at 28 d in healthy group was significantly higher than hospitalization group ( P<0.05). Multivariate logistic regression analysis showed that maternal complications during pregnancy ( OR=5.889, 95% CI 1.621-21.399, P=0.007) and neonatal antibiotic use ( OR=5.615, 95% CI 1.833-17.221, P=0.003) were risk factors and formula feeding ( OR=0.389, 95% CI 0.193-0.786, P=0.008) was a protective factor for VKD. Conclusions:VKD is common in neonates. The serum vitamin K 1 level increases significantly after preventive vitamin K 1 supplementation. The vitamin K 1 levels of hospitalized full-term neonates at 14 d and 28 d are higher than hospitalized preterm neonates. The levels of vitamin K 1 at 28 d in hospitalized neonates are influenced by feeding methods, maternal complications during pregnancy and neonatal antibiotic use.