OBJECTIVES: The primary objective was to determine levels of C3-epi-25(OH)D in very low birth weight infants. The secondary objective was to evaluate the possible influence of preterm birth, intrauterine growth restriction (IUGR), and season of birth on the production of C3-epimers. METHODS: A total of 127 infants with birth weight less than 1,500 g met the inclusion criteria of the study. We examined 25-hydroxyvitamin-D [25(OH)D] levels and C3-epi-25(OH)D in maternal serum before labor, and in cord blood and infants' serum on days 14 and 28, and at discharge. RESULTS: The mean levels (±SD) of C3-epi-25(OH)D of the cord, on day 14, on day 28, and at discharge were 2.2 (2.9), 7.7 (5.5), 11.7 (7.6) and 14.9 (11.7) nmol/L respectively. The proportion of total 25(OH)D as the C3-epimer was 6.9% (cord), 16.3% (day 14), 22.4% (day 28) and 23.3% (discharge). A statistically significant correlation between 25(OH)D and C3-epi-25(OH)D can be demonstrated from birth. The severity of immaturity and IUGR did not affect the production of C3-epimers. In summer/autumn vs. winter/spring, the mean (SD) percentage of total 25(OH)D as the C3-epimer significantly differs only in maternal serum samples and umbilical cord samples (p value <0.001). CONCLUSIONS: The production of C3-epi-25(OH)D is functional even in the most immature newborns, has fetal origins, and is largely dependent on circulating 25(OH)D. At the end of the first month of life, C3-epimers make up more than 20% of 25(OH)D.

Department of Obstetrics and Gynecology Faculty of Medicine Hradec Kralove Charles University Prague University Hospital Hradec Kralove Hradec Kralove Czech Republic

Department of Paediatrics Faculty of Medicine Hradec Kralove Charles University Prague University Hospital Hradec Kralove Hradec Kralove Czech Republic

Institute of Clinical Biochemistry and Diagnostics Faculty of Medicine Hradec Kralove University Hospital Hradec Kralove Hradec Kralove Czech Republic

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