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Published on: October 10, 2025
Fibroblast growth factor 23 concentrations in healthy term infants during the early postpartum period
Masanori Takaiwa1, Kunihiko Aya, Takayuki Miyai
1Department of Pediatrics, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan; Department of Pediatrics, Matsuyama Red Cross Hospital, Ehime, Japan.
Insights
Fibroblast growth factor 23 (FGF23) levels and fragmentation change significantly in newborns. This fragmentation impacts phosphate (Pi) homeostasis in early infant life.
Area of Science:
- Endocrinology
- Neonatal Physiology
- Mineral Metabolism
Background:
- Fibroblast growth factor 23 (FGF23) is a key regulator of phosphate (Pi) and vitamin D homeostasis.
- Early postpartum infants exhibit notable shifts in serum calcium (Ca), Pi, parathyroid hormone (PTH), and 1,25-(OH)2D levels.
- The specific role of FGF23 in neonatal mineral metabolism remains largely uncharacterized.
Purpose of the Study:
- To investigate the significance of FGF23 in early postpartum mineral metabolism.
- To quantify circulating FGF23 levels in umbilical cord blood and in infants at 5 days of life.
- To compare neonatal FGF23 levels with those of healthy adults.
Main Methods:
- Measurement of intact and C-terminal FGF23 using ELISA in cord blood, 5-day-old infants, and adult controls.
- Analysis of FGF23 fragmentation using immunoprecipitation assays.
- Statistical analysis including two-way ANOVA and Tukey's test.
Main Results:
- C-terminal FGF23 levels were higher in cord blood and 5-day-old infants compared to adults.
- Intact FGF23 levels were significantly lower in cord blood compared to 5-day-old infants and adults.
- Immunoprecipitation revealed abundant fragmented FGF23 (18kDa) and low intact FGF23 (32kDa) in cord blood.
Conclusions:
- The intact FGF23/C-terminal FGF23 ratio is markedly reduced in the early postpartum period due to FGF23 fragmentation.
- FGF23 fragmentation during early neonatal life may play a crucial role in maintaining phosphate homeostasis in healthy term infants.
Abstract:
Fibroblast growth factor 23 (FGF23) is a potent regulator of Pi and 1,25-(OH)(2)D homeostasis. Early postpartum infants show intriguing changes in serum levels of Ca, Pi, PTH and 1,25-(OH)(2)D. However, the role of FGF23 in the early neonatal mineral metabolism has not been clarified. In order to evaluate the significance of FGF23 during the early postpartum period, we examined the circulating FGF23 levels using an intact FGF23 ELISA and a C-terminal FGF23 ELISA either in 22 umbilical cord blood samples (the cord blood) or in 22 term infants at 5days of life (the 5-day-old infant). We also compared these ranges with those of 11 healthy adults. Data were expressed as mean+/-SD, and analyzed by two-way ANOVA, followed by the Tukey's test. C-terminal FGF23 in the cord blood, the 5-day-old infants and the healthy adults were 73.3+/-22.4, 81.0+/-28.2 and 39.0+/-7.8 RU/ml, respectively. Intact FGF23 in the cord blood, the 5-day-old infants and the healthy adults were 3.9+/-1.6, 21.8+/-17.6, and 27.6+/-7.3 pg/ml, respectively. Immunoprecipitation assays using anti-FGF23 antibodies demonstrated that the intact 32 kDa FGF23 was low and the fragmented FGF23 of 18kDa was abundant in the cord blood compared with those in the healthy adults. In conclusion, our observations indicated that the intact FGF23/C-terminal FGF23 ratio was very low due to the fragmentation of FGF23 during the early postpartum period and might have a considerable contribution to the Pi homeostasis in the healthy term infants.
